Anal cancer is a rare condition that forms in or around the anus.

About half of all anal cancers are diagnosed before the malignancy has spread beyond the main site, while about a third of all anal cancers are diagnosed after it has spread to the lymph nodes only. About one tenth of all anal cancers are diagnosed after the cancer has spread to distant organs.

Anal infection with human papillomavirus (HPV) is a major risk factor for anal cancer. HPV is the virus that causes anal warts. According to the American Cancer Society, 85 percent of anal cancers are associated with persistent infection with this sexually transmitted virus. Although an HPV vaccine is now in use for the prevention of cervical cancer, it is currently not being given to prevent anal cancer.

According to both the American Cancer Society and National Cancer Institute, other risk factors for anal cancer include being more than 50 years old, having many sexual partners, having receptive anal intercourse, having a weakened immune system, and being a smoker.

When found early, anal cancer is treatable. Depending on where the cancer is located, surgery may not be necessary.