cancer cancer cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. these contrast with benign tumors, which do not spread. possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements. while these symptoms may indicate cancer, they can also have other causes. over 100 types of cancers affect humans. cancerother namesmalignant tumor, malignant neoplasma coronal ct scan showing a malignant mesotheliomalegend: → tumor ←, ✱ central pleural effusion, 1 & 3 lungs, 2 spine, 4 ribs, 5 aorta, 6 spleen, 7 & 8 kidneys, 9 liverpronunciation/ˈkænsər/ (listen) specialtyoncologysymptomslump, abnormal bleeding, prolonged cough, unexplained weight loss, change in bowel movementsrisk factorsexposure to carcinogens, tobacco, obesity, poor diet, lack of physical activity, excessive alcohol, certain infectionstreatmentradiation therapy, surgery, chemotherapy, targeted therapyprognosisaverage five-year survival 66% (usa)frequency24 million annually (2019)deaths10 million annually (2019) tobacco use is the cause of about 22% of cancer deaths. another 10% are due to obesity, poor diet, lack of physical activity or excessive drinking of alcohol. other factors include certain infections, exposure to ionizing radiation, and environmental pollutants. in the developing world, 15% of cancers are due to infections such as helicobacter pylori, hepatitis b, hepatitis c, human papillomavirus infection, epstein–barr virus and human immunodeficiency virus (hiv). these factors act, at least partly, by changing the genes of a cell. typically, many genetic changes are required before cancer develops. approximately 5–10% of cancers are due to inherited genetic defects. cancer can be detected by certain signs and symptoms or screening tests. it is then typically further investigated by medical imaging and confirmed by biopsy. the risk of developing certain cancers can be reduced by not smoking, maintaining a healthy weight, limiting alcohol intake, eating plenty of vegetables, fruits, and whole grains, eating resistant starch, vaccination against certain infectious diseases, limiting consumption of processed meat and red meat, and limiting exposure to direct sunlight. early detection through screening is useful for cervical and colorectal cancer. the benefits of screening for breast cancer are controversial. cancer is often treated with some combination of radiation therapy, surgery, chemotherapy and targeted therapy. pain and symptom management are an important part of care. palliative care is particularly important in people with advanced disease. the chance of survival depends on the type of cancer and extent of disease at the start of treatment. in children under 15 at diagnosis, the five-year survival rate in the developed world is on average 80%. for cancer in the united states, the average five-year survival rate is 66% for all ages. in 2015, about 90.5 million people worldwide had cancer. in 2019, annual cancer cases grew by 23.6 million people and there were 10 million deaths worldwide, representing over the previous decade increases of 26% and 21%, respectively. the most common types of cancer in males are lung cancer, prostate cancer, colorectal cancer, and stomach cancer. in females, the most common types are breast cancer, colorectal cancer, lung cancer, and cervical cancer. if skin cancer other than melanoma were included in total new cancer cases each year, it would account for around 40% of cases. in children, acute lymphoblastic leukemia and brain tumors are most common, except in africa, where non-hodgkin lymphoma occurs more often. in 2012, about 165,000 children under 15 years of age were diagnosed with cancer. the risk of cancer increases significantly with age, and many cancers occur more commonly in developed countries. rates are increasing as more people live to an old age and as lifestyle changes occur in the developing world. the global total economic costs of cancer were estimated at us$1.16 trillion (equivalent to $1.44 trillion in 2021) per year as of 2010. etymology and definitions the word comes from the ancient greek καρκίνος, meaning 'crab' and 'tumor'. greek physicians hippocrates and galen, among others, noted the similarity of crabs to some tumors with swollen veins. the word was introduced in english in the modern medical sense around 1600. cancers comprise a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body. 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. all tumor cells show the six hallmarks of cancer. these characteristics are required to produce a malignant tumor. they include: cell growth and division absent the proper signals continuous growth and division even given contrary signals avoidance of programmed cell death limitless number of cell divisions promoting blood vessel construction invasion of tissue and formation of metastases the progression from normal cells to cells that can form a detectable mass to outright cancer involves multiple steps known as malignant progression. signs and symptoms main article: cancer signs and symptoms symptoms of cancer metastasis depend 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 cancer's type and location. few symptoms are specific. many frequently occur in individuals who have other conditions. cancer can be difficult to diagnose and can be considered a "great imitator." people may become anxious or depressed post-diagnosis. the risk of suicide in people with cancer is approximately double. 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 can lead to symptoms such as coughing up blood (lung cancer), anemia or rectal bleeding (colon cancer), blood in the urine (bladder cancer), or abnormal vaginal bleeding (endometrial or cervical cancer). although localized pain may occur in advanced cancer, the initial tumor is usually painless. some cancers can cause a buildup of fluid within the chest or abdomen. systemic symptoms systemic symptoms may occur due to the body's response to the cancer. this may include fatigue, unintentional weight loss, or skin changes. some cancers can cause a systemic inflammatory state that leads to ongoing muscle loss and weakness, known as cachexia. some cancers, such as hodgkin's disease, leukemias, and liver or kidney cancers, can cause a persistent fever. some systemic symptoms of cancer are caused by hormones or other molecules produced by the tumor, known as paraneoplastic syndromes. common paraneoplastic syndromes include hypercalcemia, which can cause altered mental state, constipation and dehydration, or hyponatremia, which can also cause altered mental status, vomiting, headaches, or seizures. metastasis main article: metastasis 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. most cancer deaths are due to cancer that has metastasized. 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. causes main article: causes of cancer the ghs hazard pictogram for carcinogenic substances share of cancer deaths attributed to tobacco in 2016. the majority of cancers, some 90–95% of cases, are due to genetic mutations from environmental and lifestyle factors. the remaining 5–10% are due to inherited genetics. environmental refers to any cause that is not inherited, such as lifestyle, economic, and behavioral factors and not merely pollution. common environmental factors that contribute to cancer death include tobacco use (25–30%), diet and obesity (30–35%), infections (15–20%), radiation (both ionizing and non-ionizing, up to 10%), lack of physical activity, and pollution. psychological stress does not appear to be a risk factor for the onset of cancer, though it may worsen outcomes in those who already have cancer. 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, however factors that may have contributed to the development of cancer can be transmissible; such as oncoviruses like hepatitis b, epstein-barr virus and hiv. chemicals further information: alcohol and cancer and smoking and cancer the incidence of lung cancer is highly correlated with smoking. exposure to particular substances have been linked to specific types of cancer. these substances are called carcinogens. tobacco smoke, for example, causes 90% of lung cancer. it also causes cancer in the larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas. tobacco smoke contains over fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons. tobacco is responsible for about one in five cancer deaths worldwide and about one in three in the developed world. 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. 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. cancer from work-related substance exposures may cause between 2 and 20% of cases, causing at least 200,000 deaths. cancers such as lung cancer and mesothelioma can come from inhaling tobacco smoke or asbestos fibers, or leukemia from exposure to benzene. exposure to perfluorooctanoic acid (pfoa), which is predominantly used in the production of teflon, is known to cause two kinds of cancer. diet and exercise main article: diet and cancer diet, physical inactivity, and obesity are related to up to 30–35% of cancer deaths. 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. 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. 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. more than half of the effect from the 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. aflatoxin b1, a frequent food contaminant, causes liver cancer. betel nut chewing can cause oral cancer. 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 while colon cancer is more common in the united states. immigrant cancer profiles mirror those of their new country, often within one generation. infection main article: infectious causes of cancer worldwide approximately 18% of cancer deaths are related to infectious diseases. this proportion ranges from a high of 25% in africa to less than 10% in the developed world. viruses are the usual infectious agents that cause cancer but cancer bacteria and parasites may also play a role. oncoviruses (viruses that can cause cancer) include human papillomavirus (cervical cancer), epstein–barr virus (b-cell lymphoproliferative disease and nasopharyngeal carcinoma), kaposi's sarcoma herpesvirus (kaposi's sarcoma and primary effusion lymphomas), hepatitis b and hepatitis c viruses (hepatocellular carcinoma) and human t-cell leukemia virus-1 (t-cell