Anal cancer is cancer that starts in the anus. The anus is the opening at the end of your rectum. The rectum is the last part of your large intestine where solid waste from food (stool) is stored. Stool leaves your body through the anus when you have a bowel movement. Anal cancer is fairly rare. It spreads slowly and is easy to treat before it spreads.
Anal cancer can start anywhere in the anus. Where it starts determines the kind of cancer it is.
• Squamous cell carcinoma. This is the most common type of anal cancer. It starts in cells that line the anal canal and grow into the deeper tissue.
• Cloacogenic carcinoma. Almost all the rest of anal cancers are tumors that start in cells lining the area between the anus and rectum. Cloacogenic carcinoma looks different than squamous cell cancers, but behaves similarly and is treated the same.
• Adenocarcinoma. This type of anal cancer is rare in the United States. It starts in the anal glands below the anal surface and is often more advanced when it is found.
• Skin cancer. Some cancers form outside the anus in the perianal area. This area is mainly skin. The tumors here are skin cancers and are treated as skin cancer.
The cause of anal cancer is unclear. However, there is a link between anal cancer and the human papillomavirus or HPV infection. HPV is a sexually transmitted virus that has been linked to other cancers as well.
Other major risk factors include:
• HIV/AIDS infection. Anal cancer is more common among HIV/AIDS positive men who have sex with other men.
• Sexual activity. Having many sexual partners and having anal sex are both major risks. This may be due to the increased risk for HPV and HIV/AIDS infection.
• Smoking. Quitting will reduce your risk for anal cancer.
• Weak immune system. HIV/AIDS, organ transplants, certain medicines, and other conditions that weaken the immune system increase your risk.
• Age. Most people who have anal cancer are age 50 or older. In rare cases, it is seen in people younger than age 35.
• Sex and race. Anal cancer is more common among women than men in most groups. More African American males get anal cancer than females.