Anal cancer forms when a genetic mutation turns normal, healthy cells into abnormal cells. Healthy cells grow and multiply at a set rate, eventually dying at a set time. Abnormal cells grow and multiply out of control, and they don’t die. The accumulating abnormal cells form a mass (tumor). Cancer cells invade nearby tissues and can separate from an initial tumor to spread elsewhere in the body (metastasize).
Anal cancer is closely related to a sexually transmitted infection called human papillomavirus (HPV). Evidence of HPV is detected in the majority of anal cancers. HPV is thought to be the most common cause of anal cancers. Several factors have been found to increase the risk of anal cancer, including the following:
- Older age. Most cases of anal cancer occur in people age 50 and older.
- Many sexual partners. People who have many sexual partners over their lifetimes have a greater risk of anal cancer.
- Anal sex. People who engage in receptive anal sex have an increased risk of anal cancer especially if the person has multiple sexual partners or engages in rough anal sex.
- Smoking. Smoking cigarettes and other tobacco products can increase the risk of anal cancer, as well as many other types of cancer.Smoking may increase your risk of anal cancer.
- History of cancer. Those who have had cervical, vulvar or vaginal cancer have an increased risk of anal cancer.
- Human papillomavirus (HPV). HPV is an infection that can cause abnormal cell changes in the anus. It increases your risk of several cancers, including anal cancer and cervical cancer. HPV infection is a sexually transmitted infection that can also cause genital warts.
- Drugs or conditions that suppress your immune system. People who take drugs to suppress their immune systems (immunosuppressive drugs), including people who have received organ transplants, may have an increased risk of anal cancer.
- A weakened immune system: People with a weakened immune system, such as those with HIV or AIDS, or those who have had an organ transplant, have a higher risk of developing anal cancer.
Complications
Anal cancer rarely spreads (metastasizes) to distant parts of the body. Only a small percentage of tumors are found to have spread, but those that do are especially difficult to treat. Anal cancer that metastasizes most commonly spreads to the liver and the lungs.
It is important to note that having one or more of these risk factors does not guarantee that a person will develop anal cancer. It is also important to keep in mind that early detection and treatment of anal cancer can greatly improve a person’s chances of survival.