Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.[2][8] These contrast with benign tumors, which do not spread to other parts of the body.[8] Possible signs and symptomsinclude a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements.[1] While these symptoms may indicate cancer, they may have other causes.[1] Over 100 types of cancers affect humans.[8]
In 2015, about 90.5 million people had cancer.[6] About 14.1 million new cases occur a year (not including skin cancer other than melanoma).[11] It caused about 8.8 million deaths (15.7% of deaths).[7] The most common types of cancer in males are lung cancer, prostate cancer, colorectal cancer and stomach cancer.[19] In females, the most common types are breast cancer, colorectal cancer, lung cancer and cervical cancer.[11] If skin cancer other than melanoma were included in total new cancers each year, it would account for around 40% of cases.[20][21] In children, acute lymphoblastic leukemia and brain tumors are most common except in Africa where non-Hodgkin lymphoma occurs more often.[18] In 2012, about 165,000 children under 15 years of age were diagnosed with cancer.[19] The risk of cancer increases significantly with age and many cancers occur more commonly in developed countries.[11] Rates are increasing as more people live to an old age and as lifestyle changes occur in the developing world.[22] The financial costs of cancer were estimated at $1.16 trillion USD per year as of 2010.
कैंसर की बीमारी बड़ी तेज़ी से फैल रही है. ताज़ा आंकड़े बताते हैं कि अमरीका में बयालीस फ़ीसद मर्द और 38 फ़ीसद औरतों को कैंसर होने की आशंका है.
ब्रिटेन में तो ये आंकड़ा और भी ख़राब है. यहां 54 फ़ीसद आदमी और 48 फ़ीसद महिलाओं को कैंसर होने का डर है.
2015 में ब्रिटेन में पच्चीस लाख़ लोग इस बीमारी के शिकार थे. इसमें हर साल तीन फ़ीसद यानी चार लाख़ नए केस जुड़ जाते हैं.
ये आंकड़े बता रहे हैं कि कैंसर की बीमारी आम होने लगी है.
आख़िर इसकी वजह क्या है?
इस सवाल का जवाब पाने के लिए पहले हमें समझना होगा कि कैंसर है क्या? असल में कैंसर, इंसान के विकास की क़ुदरती प्रक्रिया का नतीजा है.
इंसान जैसे बड़े जीव कैंसर जैसी बीमारी को इसीलिए झेलते हैं क्योंकि वो बड़े और पेचीदा हैं.
जैसे विकास की प्रक्रिया के नतीजे में हमें कैंसर की बीमारी मिली है. इसी तरह की नई सोच से इस बीमारी से लड़ने की तैयारी भी हो रही है.
कैंसर कैसे होता है, ये समझने के लिए हमें अपने अंदर होने वाली क़ुदरती प्रक्रिया को समझना होगा.
हर जीव, हर इंसान का विकास, हमारे शरीर में मौजूद कोशिकाओं के बंटने से होता है. इंसान का शरीर एक कोशिका से ही बनना शुरू होता है.
नर के शुक्राणु और मादा के अंडाणु के मेल से एक गेंदनुमा कोशिका बनती है. इसी कोशिका के बार-बार के बंटवारे से हमारा विकास होता है.
जब हम 18 बरस की उम्र तक पहुंचते हैं तब तक हमारे शरीर की कोशिकाएं अरबों बार बंट चुकी होती हैं.
कोशिकाओं के बंटने की ये प्रक्रिया बेहद नियंत्रित माहौल में होती है.
जैसे कि जब आपके हाथ की उंगलियां बनती हैं तो उस दौरान कई कोशिकाएं ख़ुदकुशी करती हैं. तब जाकर आपकी दो उंगलियों के बीच जगह बनती है.
कैंसर की बीमारी भी कोशिकाओं के बंटवारे से ही होती है. फ़र्क़ बस इतना होता है कि जहां शरीर के अंगों के विकास के वक़्त कोशिकाओं का विभाजन बेहद नियंत्रित माहौल में होता है.
कैम्ब्रिज यूनिवर्सिटी के वैज्ञानिक टिमोथी वील कहते हैं कि कैंसर असल में कोशिकाओं के विभाजन की प्रक्रिया का बेक़ाबू हो जाना है.
हमारे शरीर में कोशिकाओं के इस बंटवारे पर हमारे जीन का कंट्रोल होता है.
जब कोई जीन किसी वजह से ये ज़िम्मेदारी नहीं निभा पाता तो कोशिकाओं के विभाजन की प्रक्रिया आउट ऑफ कंट्रोल हो जाती है.
आम तौर पर ऐसा नहीं होता. कोशिकाओं के बंटवारे पर हमारे जीन्स की कड़ी निगाह होती है.
जब भी कोई कोशिका, सिस्टम से बाहर होने लगती है तो जीन्स के आदेश पर उसे क़त्ल कर दिया जाता है ताकि कोशिकाओं के बंटवारे का काम आउट ऑफ कंट्रोल न हो.
ब्रिटेन के वैज्ञानिक चार्ल्स स्वांटन कहते हैं कि कोशिकाओं के बंटवारे की इस प्रक्रिया का विकास लाखों साल में हुआ है.
इस पर जीन का नियंत्रण काफ़ी हद तक रहता है. मगर कई बार बात बेक़ाबू हो जाती है. तभी इंसान को कैंसर की बीमारी होती है.
ये बीमारी कुछ गिनी चुनी कोशिकाओं के बेक़ाबू होने से होती है. मगर ये इतनी तेज़ी से फैलती हैं कि इन्हें रोक पाना नामुमकिन सा हो जाता है.
ये कोशिकाएं बेकाबू तब होती हैं, जब इनमें कोई अंदरूनी बदलाव होता है, तब ये जीन्स का फरमान मानने से इंकार करके अपनी मनमर्ज़ी से बढ़ने लगती हैं.
ये हमारे अंदर, ट्यूमर या रसौली के तौर पर सामने आता है.
क़ुदरती तौर पर विकास की प्रक्रिया को हम एक पेड़ से समझ सकते हैं.
जैसे एक बीज से एक पौधा उगता है, फिर वो पेड़ में, उसकी तमाम टहनियों में तब्दील हो जाता है. वैसे ही कैंसर की शुरुआत भी एक कोशिका के अंदर बदलाव से होती है.
जब कोशिकाओं का बंटवारा तेज़ी से बेक़ाबू होने लगता है, तो कैंसर का पौधा, पेड़ में तब्दील हो जाता है, जिसकी कई शाखाएं हो जाती हैं.
किसी भी पेड़ के ख़ात्मे के लिए उसके तने को काट दिया जाता है. वैज्ञानिक इसी तरीक़े से इंसान के भीतर कैंसर के विष वृक्ष को ख़त्म करने की सोच रहे हैं.
चार्ल्स स्वांटन और उनकी टीम इस दिशा में काम कर रही है. वो कहते हैं कि कैंसर की कोशिका, म्यूटेशन नाम की क़ुदरती प्रक्रिया से बनती है.
म्यूटेशन या तब्दीली आने का मतलब है कि उस कोशिका के जीन में अचानक से कोई हेर-फेर हो गया. इसी से कोशिकाएं बेकाबू होकर बंटने और बढ़ने लगती हैं.
वैज्ञानिक कहते हैं कि कैंसर के ख़ात्मे के लिए किसी भी कोशिका के अंदर आए इस बदलाव को निशाना बनाने से बात बन सकती है.
इससे बाक़ी कोशिकाओं को भी ख़त्म किया जा सकेगा. मगर, होता यूं है कि कोशिकाओं में बंटवारे के साथ-साथ फ़र्क़ आता जाता है.
जैसे पेड़ की कई अलग-अलग डालियां निकल आती हैं. उसी तरह कैंसर की कोशिकाओं की भी अलग-अलग टहनियां निकल आती हैं. जिनमें आपस में फ़र्क़ होता है.
ब्रिटिश वैज्ञानिक चार्ल्स स्वांटन और उनके साथी मानते हैं कि कैंसर के ख़ात्मे के लिए कोशिकाओं में आई इसी तब्दीली को टारगेट करना होगा.
क्योंकि यही इनके बेक़ाबू होने की वजह है. अगर इन तब्दील हुई कोशिकाओं पर तिहरा हमला किया जाए, तो इनका ख़ात्मा तय है.
हालांकि ये बेहद महंगा काम है. पहले तो कैंसर के मरीज़ की कोशिकाओं की पड़ताल करके ये पता लगाना होगा कि उनमें बदलाव क्या आया है.
फिर उसे निशाना बनाने का तरीक़ा तलाशना होगा. यानी हर मरीज़ के लिए ख़ास एंटीजेन तलाशना होगा, जिससे इन बेक़ाबू कोशिकाओं का काम तमाम किया जा सके.
इटली के वैज्ञानिक अल्बर्टो बार्देली भी इसी सोच की मदद से कैंसर से लड़ने की तैयारी कर रहे हैं.
वो कैंसर की बाग़ी कोशिकाओं से लड़ने के लिए उनके क्लोन तैयार करते हैं और उनकी मदद से कैंसर की कोशिकाओं को मारने का काम करते हैं.
अपने इस तजुर्बे को वो इसी साल आज़माने वाले हैं.
इन नुस्खों के कामयाब होने के लिए ज़रूरी है कि हम पहले उन तब्दीलियों को समझें जिनकी वजह से कोशिकाएं बाग़ी होती हैं.
ऐसा हमारी कोशिकाओं के डीएनए में हेर-फेर की वजह से होता है. फेफड़ों, त्वचा या गर्भाशय के कैंसर की एक जैसी ही वजह होती है.
इनमें तब्दीली अल्ट्रावायलेट किरणों की वजह से या फिर नशे की वजह से आती है.
वैसे कुछ जानकार ये कहते हैं कि कैंसर की वजह समझने और इससे लड़ने का तरीक़ा तलाशना सही है.
पर बेहतर होगा कि हम इसकी रोकथाम पर ज़ोर दें. क्योंकि कैंसर होने की कुछ ख़ास वजहें हैं. उन्हें ख़त्म करके हम कैंसर होने से ही रोक सकते हैं.
अमरीकी कैंसर सोसाइटी के ओटिस ब्राव्ले ऐसी ही सोच वाले हैं. वो कहते हैं कि पिछले बीस सालों में अमरीका में मरने की दर में पच्चीस फ़ीसद की गिरावट आई है. इसकी आधी वजह है कैंसर की रोकथाम.
अमरीका में कैंसर के कुल मामलों के एक तिहाई, सिगरेट पीने की वजह से होते हैं, तो अगर हम तंबाकू के इस्तेमाल को रोकने की कोशिश करें, तो कैंसर की रोकथाम ख़ुद ब ख़ुद हो जाएगी.
वैसे मौत की दर भले घट रही हो, कैंसर के मरीज़ बढ़ रहे हैं. इसकी वजह ये भी है कि आज हम कैंसर की बीमारी के बारे में ज़्यादा जानते हैं, इसकी पहचान भी आसानी से हो जाती है.
वैसे कैंसर के मरीज़ों की तादाद बढ़ने की एक वजह इंसान की औसत उम्र में आया बदलाव भी है. आज लोग पहले से ज़्यादा जीते हैं. लंबी उम्र होने का मतलब है कैंसर होने की ज़्यादा आशंका.
Cancers are a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body.[2][8] They form a subset of neoplasms. A neoplasm or tumor is a group of cells that have undergone unregulated growth and will often form a mass or lump, but may be distributed diffusely.[24][25]
All tumor cells show the six hallmarks of cancer. These characteristics are required to produce a malignant tumor. They include:[26]
The progression from normal cells to cells that can form a detectable mass to outright cancer involves multiple steps known as malignant progression.[27][28]
Symptoms of cancer metastasisdepend on the location of the tumor.
When cancer begins, it produces no symptoms. Signs and symptoms appear as the mass grows or ulcerates. The findings that result depend on the cancer's type and location. Few symptoms are specific. Many frequently occur in individuals who have other conditions. Cancer is a "great imitator". Thus, it is common for people diagnosed with cancer to have been treated for other diseases, which were hypothesized to be causing their symptoms.[29]
People may become anxious or depressed post-diagnosis. The risk of suicide in people with cancer is approximately double.[30]
Local symptoms
Local symptoms may occur due to the mass of the tumor or its ulceration. For example, mass effects from lung cancer can block the bronchus resulting in cough or pneumonia; esophageal cancer can cause narrowing of the esophagus, making it difficult or painful to swallow; and colorectal cancer may lead to narrowing or blockages in the bowel, affecting bowel habits. Masses in breasts or testicles may produce observable lumps. Ulceration can cause bleeding that, if it occurs in the lung, will lead to coughing up blood, in the bowels to anemiaor rectal bleeding, in the bladder to blood in the urine and in the uterus to vaginal bleeding. Although localized pain may occur in advanced cancer, the initial swelling is usually painless. Some cancers can cause a buildup of fluid within the chest or abdomen.[29]
Cancer can spread from its original site by local spread, lymphatic spread to regional lymph nodes or by hematogenous spread via the blood to distant sites, known as metastasis. When cancer spreads by a hematogenous route, it usually spreads all over the body. However, cancer 'seeds' grow in certain selected site only ('soil') as hypothesized in the soil and seed hypothesis of cancer metastasis. The symptoms of metastatic cancers depend on the tumor location and can include enlarged lymph nodes (which can be felt or sometimes seen under the skin and are typically hard), enlarged liver or enlarged spleen, which can be felt in the abdomen, pain or fracture of affected bones and neurological symptoms.[29]
The majority of cancers, some 90–95% of cases, are due to genetic mutations from environmental factors.[3] The remaining 5–10% are due to inherited genetics.[3]Environmental, as used by cancer researchers, means any cause that is not inherited genetically, such as lifestyle, economic and behavioral factors and not merely pollution.[32] Common environmental factors that contribute to cancer death include tobacco (25–30%), diet and obesity (30–35%), infections (15–20%), radiation (both ionizing and non-ionizing, up to 10%), stress, lack of physical activity and pollution.[3][33]
It is not generally possible to prove what caused a particular cancer because the various causes do not have specific fingerprints. For example, if a person who uses tobacco heavily develops lung cancer, then it was probably caused by the tobacco use, but since everyone has a small chance of developing lung cancer as a result of air pollution or radiation, the cancer may have developed for one of those reasons. Excepting the rare transmissions that occur with pregnancies and occasional organ donors, cancer is generally not a transmissible disease.[34]
Tobacco is responsible for about one in five cancer deaths worldwide[37] and about one in three in the developed world.[38] Lung cancer death rates in the United States have mirrored smoking patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently, decreases in smoking rates since the 1950s followed by decreases in lung cancer death rates in men since 1990.[39][40]
In Western Europe, 10% of cancers in males and 3% of cancers in females are attributed to alcohol exposure, especially liver and digestive tract cancers.[41] Cancer from work-related substance exposures may cause between 2 and 20% of cases,[42] causing at least 200,000 deaths.[43] Cancers such as lung cancer and mesothelioma can come from inhaling tobacco smoke or asbestos fibers, or leukemia from exposure to benzene.[43]
Diet, physical inactivity and obesity are related to up to 30–35% of cancer deaths.[3][44] In the United States excess body weight is associated with the development of many types of cancer and is a factor in 14–20% of cancer deaths.[44] A UK study including data on over 5 million people showed higher body mass index to be related to at least 10 types of cancer and responsible for around 12,000 cases each year in that country.[45] Physical inactivity is believed to contribute to cancer risk, not only through its effect on body weight but also through negative effects on the immune system and endocrine system.[44] More than half of the effect from diet is due to overnutrition (eating too much), rather than from eating too few vegetables or other healthful foods.
Some specific foods are linked to specific cancers. A high-salt diet is linked to gastric cancer.[46]Aflatoxin B1, a frequent food contaminant, causes liver cancer.[46]Betel nut chewing can cause oral cancer.[46] National differences in dietary practices may partly explain differences in cancer incidence. For example, gastric cancer is more common in Japan due to its high-salt diet[47] while colon cancer is more common in the United States. Immigrant cancer profiles develop mirror that of their new country, often within one generation.[48]
Worldwide approximately 18% of cancer deaths are related to infectious diseases.[3] This proportion ranges from a high of 25% in Africa to less than 10% in the developed world.[3]Viruses are the usual infectious agents that cause cancer but cancer bacteria and parasites may also play a role.
Ionizing radiation is not a particularly strong mutagen.[52] Residential exposure to radon gas, for example, has similar cancer risks as passive smoking.[52] Radiation is a more potent source of cancer when combined with other cancer-causing agents, such as radon plus tobacco smoke.[52] Radiation can cause cancer in most parts of the body, in all animals and at any age. Children and adolescents are twice as likely to develop radiation-induced leukemia as adults; radiation exposure before birth has ten times the effect.[52]
Medical use of ionizing radiation is a small but growing source of radiation-induced cancers. Ionizing radiation may be used to treat other cancers, but this may, in some cases, induce a second form of cancer.[52] It is also used in some kinds of medical imaging.[53]
Prolonged exposure to ultraviolet radiation from the sun can lead to melanoma and other skin malignancies.[54] Clear evidence establishes ultraviolet radiation, especially the non-ionizing medium wave UVB, as the cause of most non-melanoma skin cancers, which are the most common forms of cancer in the world.[54]
The vast majority of cancers are non-hereditary (sporadic). Hereditary cancers are primarily caused by an inherited genetic defect. Less than 0.3% of the population are carriers of a genetic mutation that has a large effect on cancer risk and these cause less than 3–10% of cancer.[57] Some of these syndromes include: certain inherited mutations in the genes BRCA1 and BRCA2 with a more than 75% risk of breast cancer and ovarian cancer,[57] and hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome), which is present in about 3% of people with colorectal cancer,[58] among others.
Physical agents
Some substances cause cancer primarily through their physical, rather than chemical, effects.[59] A prominent example of this is prolonged exposure to asbestos, naturally occurring mineral fibers that are a major cause of mesothelioma (cancer of the serous membrane) usually the serous membrane surrounding the lungs.[59] Other substances in this category, including both naturally occurring and synthetic asbestos-like fibers, such as wollastonite, attapulgite, glass wool and rock wool, are believed to have similar effects.[59] Non-fibrous particulate materials that cause cancer include powdered metallic cobalt and nickel and crystalline silica (quartz, cristobalite and tridymite).[59] Usually, physical carcinogens must get inside the body (such as through inhalation) and require years of exposure to produce cancer.[59]
Physical trauma resulting in cancer is relatively rare.[60] Claims that breaking bones resulted in bone cancer, for example, have not been proven.[60] Similarly, physical trauma is not accepted as a cause for cervical cancer, breast cancer or brain cancer.[60] One accepted source is frequent, long-term application of hot objects to the body. It is possible that repeated burns on the same part of the body, such as those produced by kanger and kairo heaters (charcoal hand warmers), may produce skin cancer, especially if carcinogenic chemicals are also present.[60] Frequent consumption of scalding hot tea may produce esophageal cancer.[60] Generally, it is believed that cancer arises, or a pre-existing cancer is encouraged, during the process of healing, rather than directly by the trauma.[60] However, repeated injuries to the same tissues might promote excessive cell proliferation, which could then increase the odds of a cancerous mutation.
Chronic inflammation has been hypothesized to directly cause mutation.[60][61] Inflammation can contribute to proliferation, survival, angiogenesis and migration of cancer cells by influencing the tumor microenvironment.[62][63]Oncogenes build up an inflammatory pro-tumorigenic microenvironment.[64]
Hormones are important agents in sex-related cancers, such as cancer of the breast, endometrium, prostate, ovary and testis and also of thyroid cancer and bone cancer.[65] For example, the daughters of women who have breast cancer have significantly higher levels of estrogen and progesterone than the daughters of women without breast cancer. These higher hormone levels may explain their higher risk of breast cancer, even in the absence of a breast-cancer gene.[65] Similarly, men of African ancestry have significantly higher levels of testosterone than men of European ancestry and have a correspondingly higher level of prostate cancer.[65] Men of Asian ancestry, with the lowest levels of testosterone-activating androstanediol glucuronide, have the lowest levels of prostate cancer.[65]
Other factors are relevant: obese people have higher levels of some hormones associated with cancer and a higher rate of those cancers.[65] Women who take hormone replacement therapy have a higher risk of developing cancers associated with those hormones.[65] On the other hand, people who exercise far more than average have lower levels of these hormones and lower risk of cancer.[65]Osteosarcoma may be promoted by growth hormones.[65] Some treatments and prevention approaches leverage this cause by artificially reducing hormone levels and thus discouraging hormone-sensitive cancers.[65]
Autoimmune diseases
There is an association between celiac disease and an increased risk of all cancers. People with untreated celiac disease have a higher risk, but this risk decreases with time after diagnosis and strict treatment, probably due to the adoption of a gluten-free diet, which seems to have a protective role against development of malignancy in people with celiac disease. However, the delay in diagnosis and initiation of a gluten-free diet seems to increase the risk of malignancies.[67] Rates of gastrointestinal cancers are increased in people with Crohn's disease and ulcerative colitis, due to chronic inflammation. Also, immunomodulators and biologic agents used to treat these diseases may promote developing extra-intestinal malignancies.[68]
Cancer is fundamentally a disease of tissue growth regulation. In order for a normal cell to transform into a cancer cell, the genes that regulate cell growth and differentiation must be altered.[69]
The affected genes are divided into two broad categories. Oncogenes are genes that promote cell growth and reproduction. Tumor suppressor genesare genes that inhibit cell division and survival. Malignant transformation can occur through the formation of novel oncogenes, the inappropriate over-expression of normal oncogenes, or by the under-expression or disabling of tumor suppressor genes. Typically, changes in multiple genes are required to transform a normal cell into a cancer cell.[70]
Genetic changes can occur at different levels and by different mechanisms. The gain or loss of an entire chromosome can occur through errors in mitosis. More common are mutations, which are changes in the nucleotide sequence of genomic DNA.
Large-scale mutations involve the deletion or gain of a portion of a chromosome. Genomic amplification occurs when a cell gains copies (often 20 or more) of a small chromosomal locus, usually containing one or more oncogenes and adjacent genetic material. Translocation occurs when two separate chromosomal regions become abnormally fused, often at a characteristic location. A well-known example of this is the Philadelphia chromosome, or translocation of chromosomes 9 and 22, which occurs in chronic myelogenous leukemia and results in production of the BCR-ablfusion protein, an oncogenic tyrosine kinase.
Small-scale mutations include point mutations, deletions, and insertions, which may occur in the promoter region of a gene and affect its expression, or may occur in the gene's coding sequence and alter the function or stability of its protein product. Disruption of a single gene may also result from integration of genomic material from a DNA virus or retrovirus, leading to the expression of viral oncogenes in the affected cell and its descendants.
Replication of the data contained within the DNA of living cells will probabilistically result in some errors (mutations). Complex error correction and prevention is built into the process and safeguards the cell against cancer. If a significant error occurs, the damaged cell can self-destruct through programmed cell death, termed apoptosis. If the error control processes fail, then the mutations will survive and be passed along to daughter cells.
Some environments make errors more likely to arise and propagate. Such environments can include the presence of disruptive substances called carcinogens, repeated physical injury, heat, ionising radiation or hypoxia.[71]
The errors that cause cancer are self-amplifying and compounding, for example:
A mutation in the error-correcting machinery of a cell might cause that cell and its children to accumulate errors more rapidly.
A further mutation in an oncogene might cause the cell to reproduce more rapidly and more frequently than its normal counterparts.
A further mutation may cause loss of a tumor suppressor gene, disrupting the apoptosis signaling pathway and immortalizing the cell.
A further mutation in the signaling machinery of the cell might send error-causing signals to nearby cells.
The transformation of a normal cell into cancer is akin to a chain reaction caused by initial errors, which compound into more severe errors, each progressively allowing the cell to escape more controls that limit normal tissue growth. This rebellion-like scenario is an undesirable survival of the fittest, where the driving forces of evolution work against the body's design and enforcement of order. Once cancer has begun to develop, this ongoing process, termed clonal evolution, drives progression towards more invasive stages.[72] Clonal evolution leads to intra-tumour heterogeneity (cancer cells with heterogeneous mutations) that complicates designing effective treatment strategies.
Characteristic abilities developed by cancers are divided into categories, specifically evasion of apoptosis, self-sufficiency in growth signals, insensitivity to anti-growth signals, sustained angiogenesis, limitless replicative potential, metastasis, reprogramming of energy metabolism and evasion of immune destruction.[27][28]
The central role of DNA damage and epigenetic defects in DNA repair genes in carcinogenesis
The classical view of cancer is a set of diseases that are driven by progressive genetic abnormalities that include mutations in tumor-suppressor genes and oncogenes and chromosomal abnormalities. Later epigenetic alterations' role was identified.[73]
Epigenetic alterations refer to functionally relevant modifications to the genome that do not change the nucleotide sequence. Examples of such modifications are changes in DNA methylation (hypermethylation and hypomethylation), histone modification[74] and changes in chromosomal architecture (caused by inappropriate expression of proteins such as HMGA2 or HMGA1).[75] Each of these alterations regulates gene expression without altering the underlying DNA sequence. These changes may remain through cell divisions, last for multiple generations and can be considered to be epimutations (equivalent to mutations).
Epigenetic alterations occur frequently in cancers. As an example, one study listed protein coding genes that were frequently altered in their methylation in association with colon cancer. These included 147 hypermethylated and 27 hypomethylated genes. Of the hypermethylated genes, 10 were hypermethylated in 100% of colon cancers and many others were hypermethylated in more than 50% of colon cancers.[76]
While epigenetic alterations are found in cancers, the epigenetic alterations in DNA repair genes, causing reduced expression of DNA repair proteins, may be of particular importance. Such alterations are thought to occur early in progression to cancer and to be a likely cause of the genetic instability characteristic of cancers.[77][78][79][80]
Reduced expression of DNA repair genes disrupts DNA repair. This is shown in the figure at the 4th level from the top. (In the figure, red wording indicates the central role of DNA damage and defects in DNA repair in progression to cancer.) When DNA repair is deficient DNA damage remains in cells at a higher than usual level (5th level) and cause increased frequencies of mutation and/or epimutation (6th level). Mutation rates increase substantially in cells defective in DNA mismatch repair[81][82] or in homologous recombinational repair (HRR).[83]Chromosomal rearrangements and aneuploidy also increase in HRR defective cells.[84]
Higher levels of DNA damage cause increased mutation (right side of figure) and increased epimutation. During repair of DNA double strand breaks, or repair of other DNA damage, incompletely cleared repair sites can cause epigenetic gene silencing.[85][86]
Deficient expression of DNA repair proteins due to an inherited mutation can increase cancer risks. Individuals with an inherited impairment in any of 34 DNA repair genes (see article DNA repair-deficiency disorder) have increased cancer risk, with some defects ensuring a 100% lifetime chance of cancer (e.g. p53 mutations).[87] Germ line DNA repair mutations are noted on the figure's left side. However, such germline mutations (which cause highly penetrant cancer syndromes) are the cause of only about 1 percent of cancers.[88]
In sporadic cancers, deficiencies in DNA repair are occasionally caused by a mutation in a DNA repair gene but are much more frequently caused by epigenetic alterations that reduce or silence expression of DNA repair genes. This is indicated in the figure at the 3rd level. Many studies of heavy metal-induced carcinogenesis show that such heavy metals cause a reduction in expression of DNA repair enzymes, some through epigenetic mechanisms. DNA repair inhibition is proposed to be a predominant mechanism in heavy metal-induced carcinogenicity. In addition, frequent epigenetic alterations of the DNA sequences code for small RNAs called microRNAs (or miRNAs). miRNAs do not code for proteins, but can "target" protein-coding genes and reduce their expression.
Cancers usually arise from an assemblage of mutations and epimutations that confer a selective advantage leading to clonal expansion (see Field defects in progression to cancer). Mutations, however, may not be as frequent in cancers as epigenetic alterations. An average cancer of the breast or colon can have about 60 to 70 protein-altering mutations, of which about three or four may be "driver" mutations and the remaining ones may be "passenger" mutations.[89]
Metastasis is the spread of cancer to other locations in the body. The dispersed tumors are called metastatic tumors, while the original is called the primary tumor. Almost all cancers can metastasize.[90] Most cancer deaths are due to cancer that has metastasized.[91]
Metastasis is common in the late stages of cancer and it can occur via the blood or the lymphatic system or both. The typical steps in metastasis are local invasion, intravasation into the blood or lymph, circulation through the body, extravasation into the new tissue, proliferation and angiogenesis. Different types of cancers tend to metastasize to particular organs, but overall the most common places for metastases to occur are the lungs, liver, brain and the bones.[90]
Most cancers are initially recognized either because of the appearance of signs or symptoms or through screening. Neither of these leads to a definitive diagnosis, which requires the examination of a tissue sample by a pathologist. People with suspected cancer are investigated with medical tests. These commonly include blood tests, X-rays, (contrast) CT scans and endoscopy.
The tissue diagnosis from the biopsy indicates the type of cell that is proliferating, its histological grade, genetic abnormalities and other features. Together, this information is useful to evaluate the prognosis and to choose the best treatment.
Cytogenetics and immunohistochemistry are other types of tissue tests. These tests provide information about molecular changes (such as mutations, fusion genes and numerical chromosome changes) and may thus also indicate the prognosis and best treatment.
Lymphoma and leukemia: These two classes arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively.[92]
Blastoma: Cancers derived from immature "precursor" cells or embryonic tissue.
Cancers are usually named using -carcinoma, -sarcoma or -blastoma as a suffix, with the Latin or Greek word for the organ or tissue of origin as the root. For example, cancers of the liver parenchyma arising from malignant epithelial cells is called hepatocarcinoma, while a malignancy arising from primitive liver precursor cells is called a hepatoblastoma and a cancer arising from fat cells is called a liposarcoma. For some common cancers, the English organ name is used. For example, the most common type of breast cancer is called ductal carcinoma of the breast. Here, the adjective ductal refers to the appearance of cancer under the microscope, which suggests that it has originated in the milk ducts.
Benign tumors (which are not cancers) are named using -oma as a suffix with the organ name as the root. For example, a benign tumor of smooth muscle cells is called a leiomyoma(the common name of this frequently occurring benign tumor in the uterus is fibroid). Confusingly, some types of cancer use the -noma suffix, examples including melanoma and seminoma.
Cancer prevention is defined as active measures to decrease cancer risk.[93] The vast majority of cancer cases are due to environmental risk factors. Many of these environmental factors are controllable lifestyle choices. Thus, cancer is generally preventable.[94] Between 70% and 90% of common cancers are due to environmental factors and therefore potentially preventable.[95]
While many dietary recommendations have been proposed to reduce cancer risks, the evidence to support them is not definitive.[14][97] The primary dietary factors that increase risk are obesity and alcohol consumption. Diets low in fruits and vegetables and high in red meat have been implicated but reviews and meta-analyses do not come to a consistent conclusion.[98][99] A 2014 meta-analysis find no relationship between fruits and vegetables and cancer.[100] Coffee is associated with a reduced risk of liver cancer.[101] Studies have linked excess consumption of red or processed meat to an increased risk of breast cancer, colon cancer and pancreatic cancer, a phenomenon that could be due to the presence of carcinogens in meats cooked at high temperatures.[102][103] In 2015 the IARC reported that eating processed meat (e.g., bacon, ham, hot dogs, sausages) and, to a lesser degree, red meat was linked to some cancers.[104][105]
Medications can be used to prevent cancer in a few circumstances.[106] In the general population, NSAIDs reduce the risk of colorectal cancer; however, due to cardiovascular and gastrointestinal side effects, they cause overall harm when used for prevention.[107]Aspirin has been found to reduce the risk of death from cancer by about 7%.[108]COX-2 inhibitorsmay decrease the rate of polyp formation in people with familial adenomatous polyposis; however, it is associated with the same adverse effects as NSAIDs.[109] Daily use of tamoxifen or raloxifene reduce the risk of breast cancer in high-risk women.[110] The benefit versus harm for 5-alpha-reductase inhibitor such as finasteride is not clear.[111]
Vitamin supplementation does not appear to be effective at preventing cancer.[112] While low blood levels of vitamin D are correlated with increased cancer risk,[113][114][115] whether this relationship is causal and vitamin D supplementation is protective is not determined.[116][117] One 2014 review found that supplements had no significant effect on cancer risk.[117]Another 2014 review concluded that vitamin D3 may decrease the risk of death from cancer (one fewer death in 150 people treated over 5 years), but concerns with the quality of the data were noted.[118]
Beta-carotene supplementation increases lung cancer rates in those who are high risk.[119]Folic acid supplementation is not effective in preventing colon cancer and may increase colon polyps.[120] It is unclear if selenium supplementation has an effect.[121]
Cancer screening is not available for many types of cancers. Even when tests are available, they may not be recommended for everyone. Universal screening or mass screeninginvolves screening everyone.[125]Selective screening identifies people who are at higher risk, such as people with a family history.[125] Several factors are considered to determine whether the benefits of screening outweigh the risks and the costs of screening.[124] These factors include:
Possible harms from the screening test: for example, X-ray images involve exposure to potentially harmful ionizing radiation
The likelihood of the test correctly identifying cancer
The likelihood that cancer is present: Screening is not normally useful for rare cancers.
Possible harms from follow-up procedures
Whether suitable treatment is available
Whether early detection improves treatment outcomes
Whether the cancer will ever need treatment
Whether the test is acceptable to the people: If a screening test is too burdensome (for example, extremely painful), then people will refuse to participate.[125]
Colon, uterine, small bowel, stomach, urinary tract
Genetic testing for individuals at high-risk of certain cancers is recommended by unofficial groups.[123][139] Carriers of these mutations may then undergo enhanced surveillance, chemoprevention, or preventative surgery to reduce their subsequent risk.[139]
The efficacy of chemotherapy depends on the type of cancer and the stage. In combination with surgery, chemotherapy has proven useful in cancer types including breast cancer, colorectal cancer, pancreatic cancer, osteogenic sarcoma, testicular cancer, ovarian cancer and certain lung cancers.[143] Chemotherapy is curative for some cancers, such as some leukemias,[144][145] ineffective in some brain tumors,[146] and needless in others, such as most non-melanoma skin cancers.[147] The effectiveness of chemotherapy is often limited by its toxicity to other tissues in the body. Even when chemotherapy does not provide a permanent cure, it may be useful to reduce symptoms such as pain or to reduce the size of an inoperable tumor in the hope that surgery will become possible in the future.
Radiation
Radiation therapy involves the use of ionizing radiation in an attempt to either cure or improve symptoms. It works by damaging the DNA of cancerous tissue, killing it. To spare normal tissues (such as skin or organs, which radiation must pass through to treat the tumor), shaped radiation beams are aimed from multiple exposure angles to intersect at the tumor, providing a much larger dose there than in the surrounding, healthy tissue. As with chemotherapy, cancers vary in their response to radiation therapy.[148][149][150]
Radiation therapy is used in about half of cases. The radiation can be either from internal sources (brachytherapy) or external sources. The radiation is most commonly low energy x-rays for treating skin cancers, while higher energy x-rays are used for cancers within the body.[151] Radiation is typically used in addition to surgery and or chemotherapy. For certain types of cancer, such as early head and neck cancer, it may be used alone.[152] For painful bone metastasis, it has been found to be effective in about 70% of patients.[152]
Surgery
Surgery is the primary method of treatment for most isolated, solid cancers and may play a role in palliation and prolongation of survival. It is typically an important part of definitive diagnosis and staging of tumors, as biopsies are usually required. In localized cancer, surgery typically attempts to remove the entire mass along with, in certain cases, the lymph nodes in the area. For some types of cancer this is sufficient to eliminate the cancer.[143]
Palliative care
Palliative care refers to treatment that attempts to help the patient feel better and may be combined with an attempt to treat the cancer. Palliative care includes action to reduce physical, emotional, spiritual and psycho-social distress. Unlike treatment that is aimed at directly killing cancer cells, the primary goal of palliative care is to improve quality of life.
People at all stages of cancer treatment typically receive some kind of palliative care. In some cases, medical specialtyprofessional organizations recommend that patients and physicians respond to cancer only with palliative care.[153] This applies to patients who:[154]
no strong evidence implies that treatment would be effective[153]
Palliative care may be confused with hospice and therefore only indicated when people approach end of life. Like hospice care, palliative care attempts to help the patient cope with their immediate needs and to increase comfort. Unlike hospice care, palliative care does not require people to stop treatment aimed at the cancer.
Multiple national medical guidelines recommend early palliative care for patients whose cancer has produced distressing symptoms or who need help coping with their illness. In patients first diagnosed with metastatic disease, palliative care may be immediately indicated. Palliative care is indicated for patients with a prognosis of less than 12 months of life even given aggressive treatment.[155][156][157]
Laser therapy uses high-intensity light to treat cancer by shrinking or destroying tumors or precancerous growths. Lasers are most commonly used to treat superficial cancers that are on the surface of the body or the lining of internal organs. It is used to treat basal cell skin cancer and the very early stages of others like cervical, penile, vaginal, vulvar, and non-small cell lung cancer. It is often combined with other treatments, such as surgery, chemotherapy, or radiation therapy. Laser-induced interstitial thermotherapy (LITT), or interstitial laser photocoagulation, uses lasers to treat some cancers using hyperthermia, which uses heat to shrink tumors by damaging or killing cancer cells. Laser are more precise than surgery and cause less damage, pain, bleeding, swelling, and scarring. A disadvantage is surgeons must have specialized training. It may be more expensive than other treatments.[159]
Alternative medicine
Complementary and alternative cancer treatments are a diverse group of therapies, practices and products that are not part of conventional medicine.[160] "Complementary medicine" refers to methods and substances used along with conventional medicine, while "alternative medicine" refers to compounds used instead of conventional medicine.[161] Most complementary and alternative medicines for cancer have not been studied or tested using conventional techniques such as clinical trials. Some alternative treatments have been investigated and shown to be ineffective but still continue to be marketed and promoted. Cancer researcher Andrew J. Vickers stated, "The label 'unproven' is inappropriate for such therapies; it is time to assert that many alternative cancer therapies have been 'disproven'."[162]
Survival rates vary by cancer type and by the stage at which it is diagnosed, ranging from majority survival to complete mortality five years after diagnosis. Once a cancer has metastasized, prognosis normally becomes much worse. About half of patients receiving treatment for invasive cancer (excluding carcinoma in situ and non-melanoma skin cancers) die from that cancer or its treatment.[22]
Survival is worse in the developing world,[22] partly because the types of cancer that are most common there are harder to treat than those associated with developed countries.[163]
Those who survive cancer develop a second primary cancer at about twice the rate of those never diagnosed.[164] The increased risk is believed to be due to the random chance of developing any cancer, the likelihood of surviving the first cancer, the same risk factors that produced the first cancer, unwanted side effects of treating the first cancer (particularly radiation therapy), and to better compliance with screening.[164]
Predicting short- or long-term survival depends on many factors. The most important are the cancer type and the patient's age and overall health. Those who are frail with other health problems have lower survival rates than otherwise healthy people. Centenarians are unlikely to survive for five years even if treatment is successful. People who report a higher quality of life tend to survive longer.[165] People with lower quality of life may be affected by depression and other complications and/or disease progression that both impairs quality and quantity of life. Additionally, patients with worse prognoses may be depressed or report poorer quality of life because they perceive that their condition is likely to be fatal.
Cancer patients have an increased risk of blood clots in veins. The use of heparin appears to improve survival and decrease the risk of blood clots.[166]
In 2008, approximately 12.7 million cancers were diagnosed (excluding non-melanoma skin cancers and other non-invasive cancers)[22] and in 2010 nearly 7.98 million people died.[167] Cancers account for approximately 13% of deaths. The most common are lung cancer (1.4 million deaths), stomach cancer (740,000), liver cancer (700,000), colorectal cancer (610,000) and breast cancer (460,000).[168] This makes invasive cancer the leading cause of death in the developed world and the second leading in the developing world.[22] Over half of cases occur in the developing world.[22]
Deaths from cancer were 5.8 million in 1990.[167] Deaths have been increasing primarily due to longer lifespans and lifestyle changes in the developing world.[22] The most significant risk factor for developing cancer is age.[169] Although it is possible for cancer to strike at any age, most patients with invasive cancer are over 65.[169] According to cancer researcher Robert A. Weinberg, "If we lived long enough, sooner or later we all would get cancer."[170] Some of the association between aging and cancer is attributed to immunosenescence,[171] errors accumulated in DNA over a lifetime[172] and age-related changes in the endocrine system.[173] Aging's effect on cancer is complicated by factors such as DNA damage and inflammation promoting it and factors such as vascular aging and endocrine changes inhibiting it.[174]
Some slow-growing cancers are particularly common, but often are not fatal. Autopsy studies in Europe and Asia showed that up to 36% of people have undiagnosed and apparently harmless thyroid cancer at the time of their deaths and that 80% of men develop prostate cancer by age 80.[175][176] As these cancers do not cause the patient's death, identifying them would have represented overdiagnosis rather than useful medical care.
The three most common childhood cancers are leukemia (34%), brain tumors (23%) and lymphomas (12%).[177] In the United States cancer affects about 1 in 285 children.[178]Rates of childhood cancer increased by 0.6% per year between 1975 and 2002 in the United States[179] and by 1.1% per year between 1978 and 1997 in Europe.[177] Death from childhood cancer decreased by half since 1975 in the United States.[178]
Engraving with two views of a Dutch woman who had a tumor removed from her neck in 1689
Cancer has existed for all of human history.[180] The earliest written record regarding cancer is from circa 1600 BC in the Egyptian Edwin Smith Papyrus and describes breast cancer.[180]Hippocrates (ca. 460 BC – ca. 370 BC) described several kinds of cancer, referring to them with the Greek word καρκίνοςkarkinos (crab or crayfish).[180] This name comes from the appearance of the cut surface of a solid malignant tumor, with "the veins stretched on all sides as the animal the crab has its feet, whence it derives its name".[181]Galen stated that "cancer of the breast is so called because of the fancied resemblance to a crab given by the lateral prolongations of the tumor and the adjacent distended veins".[182]:738Celsus (ca. 25 BC – 50 AD) translated karkinos into the Latincancer, also meaning crab and recommended surgery as treatment.[180]Galen (2nd century AD) disagreed with the use of surgery and recommended purgatives instead.[180] These recommendations largely stood for 1000 years.[180]
In the 15th, 16th and 17th centuries, it became acceptable for doctors to dissect bodies to discover the cause of death.[183] The German professor Wilhelm Fabry believed that breast cancer was caused by a milk clot in a mammary duct. The Dutch professor Francois de la Boe Sylvius, a follower of Descartes, believed that all disease was the outcome of chemical processes and that acidic lymph fluid was the cause of cancer. His contemporary Nicolaes Tulp believed that cancer was a poison that slowly spreads and concluded that it was contagious.[184]
The physician John Hill described tobacco snuff as the cause of nose cancer in 1761.[183] This was followed by the report in 1775 by British surgeon Percivall Pott that chimney sweeps' carcinoma, a cancer of the scrotum, was a common disease among chimney sweeps.[185] With the widespread use of the microscope in the 18th century, it was discovered that the 'cancer poison' spread from the primary tumor through the lymph nodes to other sites ("metastasis"). This view of the disease was first formulated by the English surgeon Campbell De Morgan between 1871 and 1874.[186]
Society and culture
Though many diseases (such as heart failure) may have a worse prognosis than most cases of cancer, cancer is the subject of widespread fear and taboos. The euphemism "after a long illness" is still commonly used, reflecting an apparent stigma.[187] This deep belief that cancer is necessarily a difficult and usually deadly disease is reflected in the systems chosen by society to compile cancer statistics: the most common form of cancer—non-melanoma skin cancers, accounting for about one-third of cancer cases worldwide, but very few deaths[188][189]—are excluded from cancer statistics specifically because they are easily treated and almost always cured, often in a single, short, outpatient procedure.[190]
Cancer is regarded as a disease that must be "fought" to end the "civil insurrection"; a War on Cancer was declared in the US. Military metaphors are particularly common in descriptions of cancer's human effects and they emphasize both the state of the patient's health and the need to take immediate, decisive actions himself, rather than to delay, to ignore, or to rely entirely on others. The military metaphors also help rationalize radical, destructive treatments.[191][192]
In the 1970s, a relatively popular alternative cancer treatment in the US was a specialized form of talk therapy, based on the idea that cancer was caused by a bad attitude.[193]People with a "cancer personality"—depressed, repressed, self-loathing and afraid to express their emotions—were believed to have manifested cancer through subconscious desire. Some psychotherapists said that treatment to change the patient's outlook on life would cure the cancer.[193] Among other effects, this belief allowed society to blame the victim for having caused the cancer (by "wanting" it) or having prevented its cure (by not becoming a sufficiently happy, fearless and loving person).[194] It also increased patients' anxiety, as they incorrectly believed that natural emotions of sadness, anger or fear shorten their lives.[194] The idea was ridiculed by Susan Sontag, who published Illness as Metaphor while recovering from treatment for breast cancer in 1978.[193] Although the original idea is now generally regarded as nonsense, the idea partly persists in a reduced form with a widespread, but incorrect, belief that deliberately cultivating a habit of positive thinking will increase survival.[194] This notion is particularly strong in breast cancer culture.[194]
One idea about why people with cancer are blamed or stigmatized, called the just-world hypothesis, is that blaming cancer on the patient's actions or attitudes allows the blamers to regain a sense of control. This is based upon the blamers' belief that the world is fundamentally just and so any dangerous illness, like cancer, must be a type of punishment for bad choices, because in a just world, bad things would not happen to good people.[195]
Economic effect
In 2007, the overall costs of cancer in the US—including treatment and indirect mortality expenses (such as lost productivity in the workplace)—was estimated to be $226.8 billion. In 2009, 32% of Hispanics and 10% of children 17 years old or younger lacked health insurance; "uninsured patients and those from ethnic minorities are substantially more likely to be diagnosed with cancer at a later stage, when treatment can be more extensive and more costly."[196]
Because cancer is a class of diseases,[197][198] it is unlikely that there will ever be a single "cure for cancer" any more than there will be a single treatment for all infectious diseases.[199]Angiogenesis inhibitors were once incorrectly thought to have potential as a "silver bullet" treatment applicable to many types of cancer.[200] Angiogenesis inhibitors and other cancer therapeutics are used in combination to reduce cancer morbidity and mortality.[201]
Experimental cancer treatments are studied in clinical trials to compare the proposed treatment to the best existing treatment. Treatments that succeeded in one cancer type can be tested against other types.[202] Diagnostic tests are under development to better target the right therapies to the right patients, based on their individual biology.[203]
Cancer research focuses on the following issues:
Agents (e.g. viruses) and events (e.g. mutations) that cause or facilitate genetic changes in cells destined to become cancer.
The precise nature of the genetic damage and the genes that are affected by it.
The consequences of those genetic changes on the biology of the cell, both in generating the defining properties of a cancer cell and in facilitating additional genetic events that lead to further progression of the cancer.
The improved understanding of molecular biology and cellular biology due to cancer research has led to new treatments for cancer since US President Richard Nixon declared the "War on Cancer" in 1971. Since then, the country has spent over $200 billion on cancer research, including resources from public and private sectors.[204] The cancer death rate (adjusting for size and age of the population) declined by five percent between 1950 and 2005.[205]
Competition for financial resources appears to have suppressed the creativity, cooperation, risk-taking and original thinking required to make fundamental discoveries, unduly favoring low-risk research into small incremental advancements over riskier, more innovative research. Other consequences of competition appear to be many studies with dramatic claims whose results cannot be replicated and perverse incentives that encourage grantee institutions to grow without making sufficient investments in their own faculty and facilities.[206][207][208][209]
Pregnancy
Cancer affects approximately 1 in 1,000 pregnant women. The most common cancers found during pregnancy are the same as the most common cancers found in non-pregnant women during childbearing ages: breast cancer, cervical cancer, leukemia, lymphoma, melanoma, ovarian cancer and colorectal cancer.[210]
Diagnosing a new cancer in a pregnant woman is difficult, in part because any symptoms are commonly assumed to be a normal discomfort associated with pregnancy. As a result, cancer is typically discovered at a somewhat later stage than average. Some imaging procedures, such as MRIs (magnetic resonance imaging), CT scans, ultrasounds and mammograms with fetal shielding are considered safe during pregnancy; some others, such as PET scans, are not.[210]
Treatment is generally the same as for non-pregnant women. However, radiation and radioactive drugs are normally avoided during pregnancy, especially if the fetal dose might exceed 100 cGy. In some cases, some or all treatments are postponed until after birth if the cancer is diagnosed late in the pregnancy. Early deliveries are often used to advance the start of treatment. Surgery is generally safe, but pelvic surgeries during the first trimester may cause miscarriage. Some treatments, especially certain chemotherapy drugs given during the first trimester, increase the risk of birth defects and pregnancy loss (spontaneous abortions and stillbirths).[210]
Elective abortions are not required and, for the most common forms and stages of cancer, do not improve the mother's survival. In a few instances, such as advanced uterine cancer, the pregnancy cannot be continued and in others, the patient may end the pregnancy so that she can begin aggressive chemotherapy.[210]
Some treatments can interfere with the mother's ability to give birth vaginally or to breastfeed.[210] Cervical cancer may require birth by Caesarean section. Radiation to the breast reduces the ability of that breast to produce milk and increases the risk of mastitis. Also, when chemotherapy is given after birth, many of the drugs appear in breast milk, which could harm the baby.[210]
Other animals
Veterinary oncology, concentrating mainly on cats and dogs, is a growing specialty in wealthy countries and the major forms of human treatment such as surgery and radiotherapy may be offered. The most common types of cancer differ, but the cancer burden seems at least as high in pets as in humans. Animals, typically rodents, are often used in cancer research and studies of natural cancers in larger animals may benefit research into human cancer.[211]
Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues.
Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.
When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors.
Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid tumors.
Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor.
Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening.
Differences between Cancer Cells and Normal Cells
Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive. One important difference is that cancer cells are less specialized than normal cells. That is, whereas normal cells mature into very distinct cell types with specific functions, cancer cells do not. This is one reason that, unlike normal cells, cancer cells continue to divide without stopping.
In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded cells.
Cancer cells may be able to influence the normal cells, molecules, and blood vessels that surround and feed a tumor—an area known as the microenvironment. For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors.
Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions. Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to “hide” from the immune system.
Tumors can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.
How Cancer Arises
Cancer is a genetic disease—that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide.
Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun. (Our Cancer Causes and Prevention section has more information.)
Each person’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur. Even within the same tumor, different cells may have different genetic changes.
In general, cancer cells have more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may have nothing to do with the cancer; they may be the result of the cancer, rather than its cause.
"Drivers" of Cancer
The genetic changes that contribute to cancer tend to affect three main types of genes—proto-oncogenes, tumor suppressor genes, and DNA repair genes. These changes are sometimes called “drivers” of cancer.
Proto-oncogenes are involved in normal cell growth and division. However, when these genes are altered in certain ways or are more active than normal, they may become cancer-causing genes (or oncogenes), allowing cells to grow and survive when they should not.
Tumor suppressor genes are also involved in controlling cell growth and division. Cells with certain alterations in tumor suppressor genes may divide in an uncontrolled manner.
DNA repair genes are involved in fixing damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes. Together, these mutations may cause the cells to become cancerous.
As scientists have learned more about the molecular changes that lead to cancer, they have found that certain mutations commonly occur in many types of cancer. Because of this, cancers are sometimes characterized by the types of genetic alterations that are believed to be driving them, not just by where they develop in the body and how the cancer cells look under the microscope.
In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumors (metastatic tumors) in other parts of the body. The metastatic tumor is the same type of cancer as the primary tumor.
A cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.
Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer. For example, breast cancer that spreads to and forms a metastatic tumor in the lung is metastatic breast cancer, not lung cancer.
Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
Treatment may help prolong the lives of some people with metastatic cancer. In general, though, the primary goal of treatments for metastatic cancer is to control the growth of the cancer or to relieve symptoms caused by it. Metastatic tumors can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease.
Tissue Changes that Are Not Cancer
Not every change in the body’s tissues is cancer. Some tissue changes may develop into cancer if they are not treated, however. Here are some examples of tissue changes that are not cancer but, in some cases, are monitored:
Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up, or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.
Dysplasia is a more serious condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form.
Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not.
An even more serious condition is carcinoma in situ. Although it is sometimes called cancer, carcinoma in situ is not cancer because the abnormal cells do not spread beyond the original tissue. That is, they do not invade nearby tissue the way that cancer cells do. But, because some carcinomas in situ may become cancer, they are usually treated.
Normal cells may become cancer cells. Before cancer cells form in tissues of the body, the cells go through abnormal changes called hyperplasia and dysplasia. In hyperplasia, there is an increase in the number of cells in an organ or tissue that appear normal under a microscope. In dysplasia, the cells look abnormal under a microscope but are not cancer. Hyperplasia and dysplasia may or may not become cancer.
Credit: Terese Winslow
Types of Cancer
There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain. Cancers also may be described by the type of cell that formed them, such as an epithelial cell or a squamous cell.
Here are some categories of cancers that begin in specific types of cells:
Carcinoma
Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope.
Carcinomas that begin in different epithelial cell types have specific names:
Adenocarcinoma is a cancer that forms in epithelial cells that produce fluids or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissues. Most cancers of the breast, colon, and prostate are adenocarcinomas.
Basal cell carcinoma is a cancer that begins in the lower or basal (base) layer of the epidermis, which is a person’s outer layer of skin.
Squamous cell carcinoma is a cancer that forms in squamous cells, which are epithelial cells that lie just beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder, and kidneys. Squamous cells look flat, like fish scales, when viewed under a microscope. Squamous cell carcinomas are sometimes called epidermoid carcinomas.
Transitional cell carcinoma is a cancer that forms in a type of epithelial tissue called transitional epithelium, or urothelium. This tissue, which is made up of many layers of epithelial cells that can get bigger and smaller, is found in the linings of the bladder, ureters, and part of the kidneys (renal pelvis), and a few other organs. Some cancers of the bladder, ureters, and kidneys are transitional cell carcinomas.
Soft tissue sarcoma forms in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints.
Sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).
Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. These cancers do not form solid tumors. Instead, large numbers of abnormal white blood cells (leukemia cells and leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections.
There are four common types of leukemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell the cancer starts in (lymphoblastic or myeloid).
Lymphoma is cancer that begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body.
There are two main types of lymphoma:
Hodgkin lymphoma – People with this disease have abnormal lymphocytes that are called Reed-Sternberg cells. These cells usually form from B cells.
Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow quickly or slowly and can form from B cells or T cells.
Multiple myeloma is cancer that begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones all through the body. Multiple myeloma is also called plasma cell myeloma and Kahler disease.
Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye.
There are different types of brain and spinal cord tumors. These tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Brain tumors can be benign (not cancer) or malignant (cancer).
Germ cell tumors are a type of tumor that begins in the cells that give rise to sperm or eggs. These tumors can occur almost anywhere in the body and can be either benign or malignant.
Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the nervous system. These tumors, which may make higher-than-normal amounts of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant.
Carcinoid tumors are a type of neuroendocrine tumor. They are slow-growing tumors that are usually found in the gastrointestinal system (most often in the rectum and small intestine). Carcinoid tumors may spread to the liver or other sites in the body, and they may secrete substances such as serotonin or prostaglandins, causing carcinoid syndrome.
अमरीकी वैज्ञानिक ओटिस ब्रॉव्ले कहते हैं कि सत्तर के पार की उम्र जाने पर कैंसर का डर बढ़ जाता है.
चालीस के पार होने पर हमारे शरीर की कुछ कोशिकाओं में ऐसी तब्दीली आती है जो कैंसर की बुनियाद बन सकती है.
हालांकि इनमें से ज़्यादातर पर हमारा शरीर ख़ुद ब ख़ुद काबू पा लेता है.
इटली के वैज्ञानिक अल्बर्टो बार्देली कहते हैं कि इंसान कैंसर पर जीत हासिल करेगा, इसकी पूरी उम्मीद है.
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ये हमारे अंदर, ट्यूमर या रसौली के तौर पर सामने आता है.
इससे बाक़ी कोशिकाओं को भी ख़त्म किया जा सकेगा. मगर, होता यूं है कि कोशिकाओं में बंटवारे के साथ-साथ फ़र्क़ आता जाता है.
I am 29 years old and I was diagnosis of Breast cancer, easy well and have a similar story except my first acceptance as a Herbal medicine denials. I wasn’t into the movement Perseid and didn’t establish connections with any of them really, just had faith in believing how they work. I say this because it was during using Dr Itua herbal medicine i now then testify herbal medicine is real, Dr Itua herbal medicine cure my breast cancer I was suffering from for 2 years. Dr Itua herbal medicine is made of natural herbs which has no side effect and is easy to drink as well. Contact Dr Itua herbal Center if you are suffering from the same Breast Cancer or any kind of human Diseases including....HIV/AIDS, HERPES COLORECTAL CANCER, BLADDER CANCER, PROSTATE CANCER, KIDNEY CANCER, LUNG CANCER, SKIN CANCER, UTERINE CANCER, LEUKEMIA, VIRUS, HEPATITIS, WOMEN/MEN INFERTILITY, LOVE SPELL,LOTTERY SPELL. HIS CONTACT EMAIL/WHATSAPP: drituaherbalcenter@gmail.com/+2348149277967
ReplyDeleteGood news this is to everyone out there with different health challenges, as I know there are still a lot of people suffering from different health issues and are therefore looking for solutions. I bring you Good news. There is a man called Dr ehiaguna a herbal practitioner who helped cure me from HSV (2), i had suffered from this diseases for the past 5 years and i have spent so much money trying to survive from it. I got my healing by taking the herbal medicine Dr ehiaguna sent to me to drink for about 14 days . 3 days after completion of the dosage, I went for a medical checkup and I was tested free from HSV. all thanks to God for leading me to Dr ehiaguna who was able to cure me completely from this deadly diseases, I’m sharing this so that other people can know of this great healer called Dr ehiaguna because I got to know him through elizabeth who he cured from HIV. I was made to understand that he can cure several other deadly diseases and infections. Don’t die in ignorance or silent and don’t let that illness take your life. Contact Dr ehiaguna through his emaildrehiaguna@gmail.com You can also whatsapp/call him on:+2348073908953 .He cure all forms of disease {1}HIV/AIDS {2}DIABETES {3}EPILEPSY {4} BLOOD CANCER {5} HPV {6} BRAIN TUMOR {7} HEPATITIS {8}COPD{9} SICKLE AND ANAEMIA.etc Be kind enough to share as you received.
DeleteI had my first outbreak of Herpes virus nearly 4 years ago. Of all the horridness, the pain and itching were unbearable. I literally freaked out as my general physician said that it had no cure. The outbreaks were not that frequent initially, but every time I fall sick, it would resurface. I had so many sores this year that I was desperate to try anything to get rid of them. Three months ago a friend suggested that I try Dr sikama remedy that's helping people get cured from HSV, COUGHING, HIV&AIDS, GENITAL HERPES, SNEEZING, HEPATITIS B, CANCER e.t.c. I quickly ordered the product and started using the remedies. I'm so relieved to say that I've not had even one outbreak for a whole month now. Moreover, I'm feeling great from within. I truly endorse this herbs product Dr sikama render to me. So if you are suffering from any deadly disease you can also contact this great man on his email: Drsikama@gmail.com call/WhatsApp:+2348130725051
ReplyDeleteGood news this is to everyone out there with different health challenges, as I know there are still a lot of people suffering from different health issues and are therefore looking for solutions. I bring you Good news. There is a man called Dr ehiaguna a herbal practitioner who helped cure me from HSV (2), i had suffered from this diseases for the past 5 years and i have spent so much money trying to survive from it. I got my healing by taking the herbal medicine Dr ehiaguna sent to me to drink for about 14 days . 3 days after completion of the dosage, I went for a medical checkup and I was tested free from HSV. all thanks to God for leading me to Dr ehiaguna who was able to cure me completely from this deadly diseases, I’m sharing this so that other people can know of this great healer called Dr ehiaguna because I got to know him through elizabeth who he cured from HIV. I was made to understand that he can cure several other deadly diseases and infections. Don’t die in ignorance or silent and don’t let that illness take your life. Contact Dr ehiaguna through his emaildrehiaguna@gmail.com You can also whatsapp/call him on:+2348073908953 .He cure all forms of disease {1}HIV/AIDS {2}DIABETES {3}EPILEPSY {4} BLOOD CANCER {5} HPV {6} BRAIN TUMOR {7} HEPATITIS {8}COPD{9} SICKLE AND ANAEMIA.etc Be kind enough to share as you received.
ReplyDelete