Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Anal cancer is an uncontrolled growth of abnormal cells in the anus. The anus is the end of the large intestine, through which solid waste leaves the body. The treatments for anal cancer and rectal cancer can differ. Doctors need to know the exact location and the specific type of cell that has become cancerous in order to choose the right treatment.

The body stores digestive waste (feces) in the rectum, the lower part of the large intestine. The feces travel through the anal canal, a short tube that connects the rectum to the anal opening where they are passed as a bowel movement.

Several types of cells line the anal canal. Anal glands, which lie underneath the lining, lubricate the anal canal to ease bowel movements.

Several types of tumors can form in the anus. These include noncancerous tumors and cancerous tumors that can spread to other parts of the body. Some noncancerous growths can turn cancerous over time.

Risk Factors

Risk factors for anal cancer include:

  • Infection with the human papillomavirus virus (HPV). HPV causes wart-like growths around the anus. The subtype HPV-16 has a particularly strong connection to anal cancer risk. However, most people with HPV do not develop anal cancer.

  • Infection with the human immunodeficiency virus (HIV). This is the virus that causes AIDS.

  • Prior history of cervical, vaginal or vulvar cancer

  • Multiple sexual partners

  • Anal intercourse

  • Frequent anal redness, swelling, and soreness

  • Abnormal anal openings (fistulas)

  • Weakened immune system

  • Prolonged use of steroid medicines, especially for patients who have had an organ transplant.

  • Smoking

Some people who develop anal cancer have no known risk factors.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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