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.

Jul. 26, 2013