Anal cancer risk factors: who is more likely to get anal cancer

What anal cancer is

The anus is the end of the large intestine, where stool leaves the body. It is joined to the rectum by the anal canal, which is about 1 to 1½ inches long. Anal cancer can start in the lining of the anal canal or in the skin just outside the anus (NCI).

In the United States, squamous cell carcinoma is the most common type of anal cancer, and studies show that human papillomavirus (HPV) infection is its main cause (NCI). Anal cancer is a different disease from cancer of the colon or rectum, which is covered in our colorectal cancer risk factors guide.

Who is more likely to get anal cancer

NCI names these risk factors (NCI causes):

• Anal HPV infection. This is the main risk factor. About nine out of every ten cases of anal cancer are found in people with anal HPV infection. People with weakened immune systems who are infected with HPV have a higher risk (NCI causes).
• HIV infection. NCI calls HIV a strong risk factor. Men who are HIV positive and have sex with men have a higher risk than men who are HIV negative and have sex with men, and women who are HIV positive have a higher risk than women who are HIV negative. Studies show that intravenous drug use or cigarette smoking may raise the risk further in people with HIV (NCI causes).
• Past cervical, vaginal or vulvar cancer. These cancers are also related to HPV, and women who have had one of them have a higher risk of anal cancer (NCI causes). See our vulvar cancer risk factors guide.
• A weakened immune system. People who take medicine to prevent rejection of an organ transplant have a higher risk. An autoimmune disorder such as Crohn disease or psoriasis may raise the risk, though NCI says it is not clear whether this comes from the condition, its treatment or both (NCI causes).
• Certain sexual practices. Receptive anal sex, having many sexual partners and sex between men raise the risk because they raise the chance of HPV infection. A history of anal warts or other sexually transmitted diseases also raises the risk, in men and women (NCI causes).
• Cigarette smoking. Current smokers have a higher risk than people who have quit or never smoked (NCI causes).

MedlinePlus gives the same list: high-risk HPV infection, a weakened immune system from HIV or from medicines taken after an organ transplant, past vulvar, vaginal or cervical cancer, many sexual partners, anal sex and smoking. It adds that anyone can get anal cancer (MedlinePlus). NCI notes that many risk factors do not directly cause cancer; they raise the chance of the cell damage that may lead to it (NCI causes).

Signs to check with a doctor

NCI lists bleeding from the anus or rectum, a lump near the anus, pain or pressure in the area around the anus, itching or discharge from the anus, and a change in bowel habits (NCI symptoms). MedlinePlus gives narrower stools, having to go more often or bowel incontinence as examples of a change in bowel habits (MedlinePlus). NCI says these signs may be caused by anal cancer or by other conditions (NCI symptoms). Our hemorrhoids risk factors guide covers another condition behind anal bleeding.

How it is diagnosed

A provider will ask about your symptoms and your family health history, and may do a digital rectal exam (a gloved finger feels the lower rectum for lumps). Tests can include an anoscopy (a short, lighted tube to look at the anus and lower rectum), a proctoscopy, an ultrasound probe placed in the rectum, and a biopsy (MedlinePlus).

Lowering the risk

• HPV vaccine. Studies show that HPV vaccination lowers the risk of anal cancer, and the vaccine may work best when it is given before a person is exposed to HPV (NCI prevention). Our HPV vaccine age check shows who it is recommended for, by age.
• Not smoking. MedlinePlus says getting an HPV vaccine and not smoking may lower your risk (MedlinePlus). Our quit smoking help check covers the help available.
• Condoms. It is not known whether condoms protect against anal HPV infection (NCI prevention). MedlinePlus adds that latex condoms used every time help prevent HIV, a risk factor for anal cancer, and other sexually transmitted infections (MedlinePlus). See our HIV screening check.
• Screening for people with HIV. MedlinePlus says adults with HIV should get an anal cancer screening every year, including a digital rectal exam, with an anoscopy if anything unusual is found (MedlinePlus). NCI says treating high-grade precancerous anal lesions lowers the chance of anal cancer in people with HIV (NCI prevention).

Common questions

Is anal cancer the same as colorectal cancer?

No. Anal cancer forms in the tissues of the anus, at the very end of the large intestine (NCI), and its main risk factor is HPV infection (NCI causes). Colorectal cancer is covered in our colorectal cancer risk factors guide.

Does having HPV mean I will get anal cancer?

No. People with healthy immune systems are usually able to fight HPV infections (NCI causes). NCI also says many risk factors raise the chance of cancer without directly causing it (NCI causes).

Can women get anal cancer?

Yes. Women who have had cervical, vaginal or vulvar cancer, and women who are HIV positive, have a higher risk (NCI causes). MedlinePlus says anyone can get anal cancer (MedlinePlus).