Cancer
group of diseases involving abnormal cell growth and spread
Cancer is a group of diseases involving uncontrolled cell growth typically resulting in tumors with the potential to invade or spread to other parts of the body. These malignant tumors contrast with benign tumors, which do not spread. Over 100 types of cancers affect humans.
About 33% of deaths from cancer are caused by tobacco and alcohol, obesity, lack of fruit and vegetables in the diet and lack of exercise. Other factors include certain infections, exposure to ionizing radiation, and environmental pollutants. Infection with specific viruses, bacteria, and parasites causes approximately 16–18% of cancers worldwide. These infectious agents include Helicobacter pylori, hepatitis B, hepatitis C, and HPV. Human immunodeficiency virus (HIV) does not directly cause cancer, but it causes immune deficiency that can increase the risk of cancer from other infections, sometimes up to several thousandfold. Vaccination against the hepatitis B virus and the human papillomavirus have been shown to nearly eliminate the risk of cancers caused by these viruses.
These environmental factors act, at least partly, by changing the genes of a cell. Typically, many genetic changes are required before cancer develops.
The public source identifies “Cancer” as group of diseases involving abnormal cell growth and spread. This brief keeps that definition visible, then builds a research path around Cancer, group and diseases.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 19, 2026. The linked authority identifier is Q12078. The Library of Congress control number is sh85019492. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
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This entry incorporates text from “Cancer” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.