|Classification and external resources|
A coronal mesothelioma
Legend: → liver.
Determining what causes cancer is complex. Many things are known to increase the risk of cancer, including  Approximately five to ten percent of cancers are entirely hereditary.
Cancer can be detected in a number of ways, including the presence of certain 
Signs and symptoms
When cancer begins it invariably produces no symptoms with signs and symptoms only appearing as the mass continues to grow or ulcerates. The findings that result depends on the type and location of the cancer. Few symptoms are specific, with many of them also frequently occurring in individuals who have other conditions. Cancer is the new “great imitator“. Thus it is not uncommon for people diagnosed with cancer to have been treated for other diseases to which it was assumed their symptoms were due.
Local symptoms may occur due to the mass of the tumor or its ulceration. For example mass effects from lung cancer can cause blockage of 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 resulting in changes in bowel habits. Masses of breast or testicles may be easily felt. Ulceration can cause bleeding which, if it occurs in the lung, will lead to coughing up blood, in the bowels to anemia or 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 build up of fluid within the chest or abdomen.
General symptoms occur due to distant effects of the cancer that are not related to direct or metastatic spread. These may include: unintentional weight loss, 
Specific constellations of systemic symptoms, termed paraneoplastic phenomena, may occur with some cancers. Examples include the appearance of myasthenia gravis in thymoma and clubbing in lung cancer.
Symptoms of metastasis are due to the spread of cancer to other locations in the body. They can include enlarged lymph nodes (which can be felt or sometimes seen under the skin and are typically hard), hepatomegaly (enlarged liver) or splenomegaly (enlarged spleen) which can be felt in the abdomen, pain or fracture of affected bones, and neurological symptoms.
Cancers are primarily an environmental disease with 90–95% of cases attributed to environmental factors and 5–10% due to genetics.
It is nearly impossible to prove what caused a cancer in any individual, because most cancers have multiple possible causes. 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, then there is a small chance that the cancer developed because of air pollution or radiation.
Cancer pathogenesis is traceable back to 
Decades of research has demonstrated the link between 
Cancer related to one’s occupation is believed to represent between 2–20% of all cases.
Diet and exercise
Diets that are low in vegetables, fruits and whole grains, and high in processed or red meats are linked with a number of cancers.
Worldwide approximately 18% of cancer deaths are related to parasites may also have an effect.
A virus that can cause cancer is called an 
Up to 10% of invasive cancers are related to radiation exposure, including both ionizing radiation and non-ionizing radiation. Additionally, the vast majority of non-invasive cancers are non-melanoma skin cancers caused by non-ionizing ultraviolet radiation.
Sources of ionizing radiation include 
Unlike chemical or physical triggers for cancer, ionizing radiation hits molecules within cells randomly. If it happens to strike a 
Medical use of ionizing radiation is a 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.
Prolonged exposure to 
Non-ionizing radio frequency radiation from mobile phones, electric power transmission, and other similar sources have been described as a possible carcinogen by the World Health Organization‘s International Agency for Research on Cancer.
The vast majority of cancers are non-hereditary (“sporadic cancers”).  among others.
Some substances cause cancer primarily through their physical, rather than chemical, effects on cells.
A prominent example of this is prolonged exposure to 
Usually, physical carcinogens must get inside the body (such as through inhaling tiny pieces) and require years of exposure to develop cancer.
Physical trauma resulting in cancer is relatively rare.
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 
Generally, it is believed that the cancer arises, or a pre-existing cancer is encouraged, during the process of repairing the trauma, rather than the cancer being caused directly by the trauma.
An individual’s hormone levels are mostly determined genetically, so this may at least partly explains the presence of some cancers that run in families that do not seem to have any cancer-causing genes.
However, non-genetic factors are also relevant: obese people have higher levels of some hormones associated with cancer and a higher rate of those cancers.
Excepting the rare transmissions that occur with pregnancies and only a marginal few organ donors, cancer is generally not a  proven using mice; however this would never happen in a real-world setting except as described above.
In non-humans, a few types of transmissible cancer have been described, wherein the cancer spreads between animals by transmission of the tumor cells themselves. This phenomenon is seen in dogs with Sticker’s sarcoma, also known as canine transmissible venereal tumor, as well as devil facial tumour disease in Tasmanian devils.
Cancer is fundamentally a disease of failure of regulation of tissue growth. In order for a normal cell to transform into a cancer cell, the genes which regulate cell growth and differentiation must be altered.
The affected genes are divided into two broad categories. Oncogenes are genes which promote cell growth and reproduction. Tumor suppressor genes are genes which 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 many genes are required to transform a normal cell into a cancer cell.
Genetic changes can occur at different levels and by different mechanisms. The gain or loss of an entire nucleotide sequence of genomic DNA.
Large-scale mutations involve the deletion or gain of a portion of a chromosome. tyrosine kinase.
Small-scale mutations include point mutations, deletions, and insertions, which may occur in the retrovirus, and resulting in the expression of viral oncogenes in the affected cell and its descendants.
Replication of the enormous amount of data contained within the DNA of living cells will 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
The errors which 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 tumour suppressor gene, disrupting the apoptosis signalling pathway and resulting in the cell becoming immortal.
- A further mutation in signaling machinery of the cell might send error-causing signals to nearby cells.
The transformation of 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 the controls that limit normal tissue growth. This rebellion-like scenario becomes 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.
Most cancers are initially recognized either because of the appearance of signs or symptoms or through endoscopy.
Cancers are classified by the type of cell that the tumor cells resemble and is therefore presumed to be the origin of the tumor. These types include:
- mesenchymal cells outside the bone marrow.
- Lymphoma and leukemia: These two classes of cancer arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively. Leukemia is the most common type of cancer in children accounting for about 30%.
- dysgerminoma, respectively).
- Blastoma: Cancers derived from immature “precursor” cells or embryonic tissue. Blastomas are more common in children than in older adults.
Cancers are usually named using -carcinoma, -sarcoma or -blastoma as a suffix, with the Latin or Greek word for the ductal carcinoma of the breast. Here, the adjective ductal refers to the appearance of the cancer under the microscope, which suggests that it has originated in the milk ducts.
Some types of cancer are named for the size and shape of the cells under a microscope, such as small cell carcinoma.
The tissue chromosome changes) that has happened in the cancer cells, and may thus also indicate the future behavior of the cancer (prognosis) and best treatment.
An invasive ductal carcinoma of the breast (pale area at the center) surrounded by spikes of whitish scar tissue and yellow fatty tissue.
An invasive colectomy specimen.
A bronchi in a lung specimen.
A large invasive mastectomy specimen.
Cancer prevention is defined as active measures to decrease the risk of cancer.background radiation, and other cases of cancer are caused through hereditary genetic disorders, and thus it is not possible to prevent all cases of cancer.
While many dietary recommendations have been proposed to reduce the risk of cancer, few have significant supporting scientific evidence.
The concept that medications can be used to prevent cancer is attractive, and evidence supports their use in a few defined circumstances.
Unlike diagnosis efforts prompted by 
Cancer screening is currently not possible for many types of cancers, and even when tests are available, they may not be recommended for everyone.  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 of cancer being 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, being extremely painful), then people will refuse to participate.
- Cost of the test.
The USPSTF recommends 
|BRCA2||Breast, ovarian, pancreatic|
|PMS2||Colon, uterine, small bowel, stomach, urinary tract|
Many management options for cancer exist with the primary ones including palliative care. Which treatments are used depends upon the type, location and grade of the cancer as well as the person’s health and wishes.
Patients at all stages of cancer treatment need some kind of palliative care to comfort them. In some cases, 
- patient has low performance status, corresponding with limited ability to care for oneself
- patient received no benefit from prior evidence-based treatments
- patient is ineligible to participate in any appropriate clinical trial
- the physician sees no strong evidence that treatment would be effective
Palliative care is often confused with end of life. Like hospice care, palliative care attempts to help the person cope with the immediate needs and to increase the person’s comfort. Unlike hospice care, palliative care does not require people to stop treatment aimed at prolonging their lives or curing the cancer.
Multiple national 
Surgery is the primary method of treatment of most isolated solid cancers and may play a role in palliation and prolongation of survival. It is typically an important part of making the definitive diagnosis and staging the tumor 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 all that is needed to eliminate the cancer.
Chemotherapy in addition to surgery has proven useful in a number of different cancer types including: breast cancer, colorectal cancer, pancreatic cancer, osteogenic sarcoma, testicular cancer, ovarian cancer, and certain lung cancers. The effectiveness of chemotherapy is often limited by toxicity to other tissues in the body.
Radiation therapy involves the use of ionizing radiation in an attempt to either cure or improve the symptoms of cancer. It is used in about half of all cases and the radiation can be from either internal sources in the form of brachytherapy or external sources. Radiation is typically used in addition to surgery and or chemotherapy but for certain types of cancer such as early head and neck cancer may be used alone. For painful bone metastasis it has been found to be effective in about 70% of people.
Cancer has a reputation as a deadly disease. Taken as a whole, about half of people receiving treatment for invasive cancer (excluding  However, the survival rates vary dramatically by type of cancer, with the range running from basically all people surviving to almost no one surviving.
Those who survive cancer are at increased risk of developing a second primary cancer at about twice the rate of those never diagnosed with cancer.
Predicting either short-term or long-term survival is difficult and depends on many factors. The most important factors are the particular kind of cancer and the patient’s age and overall health. People who are frail with many other health problems have lower survival rates than otherwise healthy people. A centenarian is unlikely to survive for five years even if the treatment is successful. People who report a higher quality of life tend to survive longer. People with lower quality of life may be affected by major depressive disorder and other complications from cancer treatment and/or disease progression that both impairs their quality of life and reduces their quantity of life. Additionally, patients with worse prognoses may be depressed or report a lower quality of life directly because they correctly perceive that their condition is likely to be fatal.
In 2008 approximately 12.7 million cancers were 
Global cancer rates have been increasing primarily due to an aging population and lifestyle changes in the developing world.
Some slow-growing cancers are particularly common. overdiagnosis rather than useful medical care.
The earliest written record regarding cancer is from 3000 BC in the Egyptian 
In the 15th, 16th and 17th centuries, it became more acceptable for doctors to 
The physician John Hill described tobacco snuff as the cause of nose cancer in 1761.
Society and culture
Though many diseases (such as 
Cancer is regarded as a disease that must be “fought” to end the “civil insurrection”; a 
In the 1970s, a relatively popular 
In 2007, the overall costs of cancer in the U.S. — 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.”
Because cancer is a class of diseases,
Cancer research is the intense scientific effort to understand disease processes and discover possible therapies.
Research about cancer causes focuses on the following issues:
- Agents (e.g. viruses) and events (e.g. mutations) which cause or facilitate genetic changes in cells destined to become cancer.
- The precise nature of the genetic damage, and the genes which 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 which lead to further progression of the cancer.
The improved understanding of 
Because cancer is largely a disease of older adults, it is not common in pregnant women. Cancer affects approximately 1 in 1,000 pregnant women.
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.
Treatment is generally the same as for non-pregnant women.
Some treatments may interfere with the mother’s ability to give birth vaginally or to breastfeed her baby.
- . Retrieved 11 May 2012.
- Holland Chp. 1
- . Retrieved 13 October 2007.
- “National Institute for Occupational Safety and Health- Occupational Cancer”. United States National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/topics/cancer/. Retrieved 13 October 2007.
- . Retrieved 31 January 2011.
- “IARC classifies radiofrequency electromagnetic fields as possibly carcinogenic to humans”. World Health Organization. http://www.iarc.fr/en/media-centre/pr/2011/pdfs/pr208_E.pdf.
- . Retrieved 31 January 2011.
- . Retrieved 27 January 2011.
- . Retrieved 27 January 2011.
- “The Nobel Prize in Physiology or Medicine 1980”. http://nobelprize.org/nobel_prizes/medicine/laureates/1980/presentation-speech.html.
- “Cancer prevention: 7 steps to reduce your risk”. Mayo Clinic. 27 September 2008. http://www.mayoclinic.com/health/cancer-prevention/CA00024. Retrieved 30 January 2010.
- “Cancer”. World Health Organization. http://www.who.int/mediacentre/factsheets/fs297/en/. Retrieved 9 January 2011.
- Holland Chp.33
- “Vitamin D Has Role in Colon Cancer Prevention”. Archived from the original on 4 December 2006. http://web.archive.org/web/20061204052746/http://www.cancer.org/docroot/NWS/content/NWS_1_1x_Vitamin_D_Has_Role_in_Colon_Cancer_Prevention.asp. Retrieved 27 July 2007.
- . Retrieved 15 November 2008.
- “Screening for Cervical Cancer”. U.S. Preventive Services Task Force. 2003. http://www.uspreventiveservicestaskforce.org/uspstf/uspscerv.htm.
- “Screening for Colorectal Cancer”. U.S. Preventive Services Task Force. 2008. http://www.uspreventiveservicestaskforce.org/uspstf/uspscolo.htm.
- “Screening for Skin Cancer”. U.S. Preventive Services Task Force. 2009. http://www.uspreventiveservicestaskforce.org/uspstf/uspsskca.htm.
- “Screening for Oral Cancer”. U.S. Preventive Services Task Force. 2004. http://www.uspreventiveservicestaskforce.org/uspstf/uspsoral.htm.
- “Lung Cancer Screening”. U.S. Preventive Services Task Force. 2004. http://www.uspreventiveservicestaskforce.org/uspstf/uspslung.htm.
- “Screening for Prostate Cancer”. U.S. Preventive Services Task Force. 2008. http://www.uspreventiveservicestaskforce.org/uspstf/uspsprca.htm.
- “Screening for Bladder Cancer”. U.S. Preventive Services Task Force. 2004. http://www.uspreventiveservicestaskforce.org/uspstf/uspsblad.htm.
- “Screening for Testicular Cancer”. U.S. Preventive Services Task Force. 2004. http://www.uspreventiveservicestaskforce.org/uspstf/uspstest.htm.
- “Screening for Ovarian Cancer”. U.S. Preventive Services Task Force. 2004. http://www.uspreventiveservicestaskforce.org/uspstf/uspsovar.htm.
- “Screening for Pancreatic Cancer”. U.S. Preventive Services Task Force. 2004. http://www.uspreventiveservicestaskforce.org/uspstf/uspspanc.htm.
- Chou, Roger; Croswell, Jennifer M.; Dana, Tracy; Bougatous, Christina; Blazina, Ian; Fu, Rongwei; Gleitsmann, Ken; Koenig, Helen C. et al. (7 October 2011). “Screening for Prostate Cancer: A Review of the Evidence for the U.S. Preventive Services Task Force”. United States Preventive Services Task Force. http://www.uspreventiveservicestaskforce.org/uspstf12/prostate/prostateart.htm. Retrieved 8 October 2011.
- “Screening for Breast Cancer”. U.S. Preventive Services Task Force. 2009. http://www.uspreventiveservicestaskforce.org/uspstf/uspsbrca.htm.
- , retrieved August 14 2012
- The American Society of Clinical Oncology made this recommendation based on various cancers. See http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_Soc_Clin_Onc.pdf, retrieved August 14 2012
- for lung cancer, see Azzoli, C. G.; Temin, S.; Aliff, T.; Baker, S.; Brahmer, J.; Johnson, D. H.; Laskin, J. L.; Masters, G. et al. (2011). “2011 Focused Update of 2009 American Society of Clinical Oncology Clinical Practice Guideline Update on Chemotherapy for Stage IV Non-Small-Cell Lung Cancer”. Journal of Clinical Oncology 29 (28): 3825–3831. edit
- for breast cancer, see Carlson, R. W.; Allred, D. C.; Anderson, B. O.; Burstein, H. J.; Carter, W. B.; Edge, S. B.; Erban, J. K.; Farrar, W. B. et al. (2009). “Breast cancer. Clinical practice guidelines in oncology”. Journal of the National Comprehensive Cancer Network : JNCCN 7 (2): 122–192. edit
- for colon cancer, see Engstrom, P. F.; Arnoletti, J. P.; Benson Ab, 3.; Chen, Y. J.; Choti, M. A.; Cooper, H. S.; Covey, A.; Dilawari, R. A. et al. (2009). “NCCN Clinical Practice Guidelines in Oncology: Colon cancer”. Journal of the National Comprehensive Cancer Network : JNCCN 7 (8): 778–831. edit
- for other general statements see Smith, T. J.; Hillner, B. E. (2011). “Bending the Cost Curve in Cancer Care”. New England Journal of Medicine 364 (21): 2060–2065. edit
- “NCCN Guidelines”. http://www.nccn.org/professionals/physician_gls/default.asp.
- “Clinical Practice Guidelines for Quality Palliative Care”. The National Consensus Project for Quality Palliative Care (NCP). http://www.nationalconsensusproject.org/guideline.pdf.
- Holland Chp. 40
- Holland Chp. 41
- . Retrieved 5 November 2009.
- “WHO Disease and injury country estimates”. World Health Organization. 2009. http://www.who.int/healthinfo/global_burden_disease/estimates_country/en/index.html. Retrieved 11 November 2009.
- WHO (October 2010). “Cancer”. World Health Organization. http://www.who.int/mediacentre/factsheets/fs297/en/. Retrieved 5 January 2011.
- Johnson, George (28 December 2010). “Unearthing Prehistoric Tumors, and Debate”. The New York Times. http://www.nytimes.com/2010/12/28/health/28cancer.html.
- . “A certain irreducible background incidence of cancer is to be expected regardless of circumstances: mutations can never be absolutely avoided, because they are an inescapable consequence of fundamental limitations on the accuracy of DNA replication, as discussed in Chapter 5. If a human could live long enough, it is inevitable that at least one of his or her cells would eventually accumulate a set of mutations sufficient for cancer to develop.”
- Paul of Aegina, 7th Century AD, quoted in Moss, Ralph W. (2004). “Galen on Cancer”. CancerDecisions. Archived from the original on 16 July 2011. http://web.archive.org/web/20110716111312/http://www.cancerdecisions.com/speeches/galen1989.html. Referenced from Michael Shimkin, Contrary to Nature, Washington, D.C.: Superintendent of Document, DHEW Publication No. (NIH) 79-720, p. 35.
- “Skin cancers”. World Health Organization. http://www.who.int/uv/faq/skincancer/en/index1.html. Retrieved 19 January 2011.
- “Cancer Facts and Figures 2012”. Journalist’s Resource.org. http://journalistsresource.org/studies/society/health/cancer-facts-figures-2012/.
- “What Is Cancer?”. National Cancer Institute. http://www.cancer.gov/cancertopics/what-is-cancer. Retrieved 17 August 2009.
- “Cancer Fact Sheet”. Agency for Toxic Substances & Disease Registry. 30 August 2002. http://www.atsdr.cdc.gov/COM/cancer-fs.html. Retrieved 17 August 2009.
- Wanjek, Christopher (16 September 2006). “Exciting New Cancer Treatments Emerge Amid Persistent Myths”. http://www.livescience.com/health/060919_bad_cancer.html. Retrieved 17 August 2009.
- Sleigh SH, Barton CL (2010). “Repurposing Strategies for Therapeutics”. Pharm Med 24 (3): 151–159. doi:10.2165/11536770-000000000-00000.
- Winther H, Jorgensen JT (2010). “Drug-Diagnostic Co-Development in Cancer”. Pharm Med 24 (6): 363–375. doi:10.2165/11586320-000000000-00000.
- Sharon Begley (16 September 2008). “Rethinking the War on Cancer”. Newsweek. http://www.newsweek.com/id/157548/page/2. Retrieved 8 September 2008.
- Kolata, Gina (23 April 2009). “Advances Elusive in the Drive to Cure Cancer”. The New York Times. http://www.nytimes.com/2009/04/24/health/policy/24cancer.html. Retrieved 5 May 2009.
- Holland, James F. (2009). Holland-Frei cancer medicine. (8th ed. ed.). New York: McGraw-Hill Medical. ISBN 978-1-60795-014-1.
- Kleinsmith, Lewis J. (2006). Principles of cancer biology. Pearson Benjamin Cummings. ISBN 978-0-8053-4003-7. http://books.google.com/books?id=LKVrAAAAMAAJ.
- Mukherjee, Siddhartha (16 November 2010). The Emperor of All Maladies: A Biography of Cancer. Simon and Schuster. ISBN 978-1-4391-0795-9.
- Pazdur, Richard; et al. (May 2009). Cancer Management: A Multidisciplinary Approach. Cmp United Business Media. ISBN 978-1-891483-62-2. http://books.google.com/books?id=wbLnPAAACAAJ. (online at cancernetwork.com)
- Tannock, Ian (2005). The basic science of oncology. McGraw-Hill Professional. ISBN 978-0-07-138774-3. http://books.google.com/books?id=Bb4F4pj2BdYC.
- Manfred Schwab (2008). Encyclopedia of Cancer (4 Volume Set). Berlin: Springer. ISBN 3-540-36847-7.
|Wikimedia Commons has media related to: Cancer|