A risk factor is anything that affects a person's 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 cancers of the lung, mouth, larynx
(voice box), bladder, kidney, colon, anus, and several other organs.
But having a risk factor, or even several risk factors, does not mean
that you will get the disease.
Human papillomavirus (HPV) infection: Most squamous cell anal cancers
seem to be linked to infection by the human papilloma virus (HPV), the
same virus thought to cause cervical cancer. There are several subtypes
of the virus, but the one most likely to cause anal cancer is called
HPV-16. This virus is most often spread by sexual contact and is more
likely to be found in people who have had many sex partners. Different
subtypes of HPV can cause genital warts (condylomas), but most people
infected with HPV do not have genital warts.
Sexual activity: Having multiple sex partners is a risk factor. Another
risk factor is anal intercourse for both men and women, particularly
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/HIV infection: 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. Another important risk factor is infection with
the human immunodeficiency virus (HIV), the virus that causes AIDS. But
effective drug treatment for HIV hasn't lowered the anal cancer rate in
people infected with HIV.