A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposure to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancer of the lung and many other cancers. But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get cancer. Also, people without risk factors can still get cancer. .

Human papilloma virus infection

Most squamous cell anal cancers seem to be linked to infection by the human papilloma virus (HPV), the same virus that causes cervical cancer. In fact, women with a history of cervical cancer (or precancer) have an increased risk of anal cancer.

HPV is a group of more than 100 related viruses. They are called papilloma viruses because some of them cause papillomas, which are more commonly known as warts. HPV is passed from one person to another during skin-to-skin contact with an infected area of the body. HPV can be spread during sex -- including vaginal intercourse, anal intercourse, and even during oral sex. There are several subtypes of the virus, but the one most likely to cause anal cancer is called HPV-16. HPV-16, as well as HPV 18, HPV 31, HPV 33, and HPV 45 are considered high-risk types of HPV because they are strongly linked to cancer. They can cause cancers of the cervix, vagina, and vulva in women, as well as cancer of the penis in men.

Other subtypes of HPV can cause warts in the genital and anal areas. The medical term for these warts is condyloma acuminatum. The 2 types of HPV that cause most cases of anal and genital warts are HPV 6 and HPV 11. They are called low-risk types of HPV because they tend to cause warts but not cancer. HPV infection can cause anal and genital warts, but most people infected with HPV do not have genital warts or any other signs of infection.

Certain factors can increase a person's risk of HPV infection, such as:

• starting to have sex at an early age
• having many sexual partners
• having sex with a partner who has had many other partners
• having unprotected sex (not using a condom)

Men who have not been circumcised are more likely to be infected with HPV and pass it on to their partners. This may be because the surface of the foreskin (which is removed by circumcision) is more easily infected by HPV.

HIV infection

People infected with the human immunodeficiency virus (HIV), the virus that causes AIDS, are much more likely to get anal cancer than those not infected with this virus. Although effective drug treatment for HIV has lowered the risk for many AIDS related diseases, it hasn't lowered the anal cancer rate.

Sexual activity

Having multiple sex partners increases the risk of infection with HIV and HPV. It also increases the risk of anal cancer. Anal intercourse also increases the risk of anal cancer in both men and women, particularly in those younger than the age of 30.

Smoking

Smoking also increases the risk of anal cancer. Current smokers are several times more likely to have cancer of the anus compared with people who do not smoke. Quitting smoking will reduce the risk. People who used to smoke but have quit are only slightly more likely to develop this cancer compared with people who never smoked.

Lowered immunity

Higher rates of anal cancer occur among people with reduced immunity, such as people who have had an organ transplant and must take medicines that suppress their immune system.

Last Medical Review: 08/17/2009
Last Revised: 08/17/2009