Anal cancer and precancer have several causes and risk factors. According to the World Health Organization, a risk factor may be 'any attribute, characteristic or exposure of an individual that increases the likelihood of developing a disease or injury'.
I had an abnormal pap over 20 years before, had a cryosurgery. I never dreamed that the HPV that caused me to have dysplasia on my cervix could result in cancer somewhere else, especially since I had normal pap smears every year after that. Eventually, I came across the Anal Cancer Foundation website by following links from several other websites. The stories of the Paulette and the Thrivers helped me feel less alone, and I felt so much in common with them.
Connie, Anal Cancer Thriver
Approximately 8,600 people will be diagnosed with anal cancer in the US and about 1,400 in the UK annually.
In almost all cases, anal cancer is caused by HPV, a virus that nearly every person has at some point in their life. The other risk factors on this page – immunosuppression, sexual activity, tobacco use and older age – all may increase the chance that an HPV infection becomes cancerous. However, there are people who don’t have these additional risk factors who also develop anal cancer.
HUMAN PAPILLOMAVIRUS (HPV)
Human papillomavirus (HPV) is the most common sexually transmitted infection in the US and UK. HPV is a skin virus that can lead to anal, cervical, vulvar, vaginal, penile and head and neck cancers. It is transmitted through skin-to-skin contact. The virus enters the DNA of the cell and causes changes that limit the body’s ability to destroy the cell even though it is infected with a virus. The impact is that the cell replicates abnormally. This may lead to groups of cellular changes that can become precancer or cancer over time.
Nearly all adults will have HPV at some point in their lifetime. Frequently HPV goes away on its own, although for some it can remain dormant in the body for decades, causing cancers to surface later in life. A small percentage of HPV infections develop into cancer. It is important to note that our immune system finds HPV the vast majority of the time, with 90% of HPV resolving within two years. There are over 100 strains of the virus, some cause cancer and some cause warts. Most people don’t even know they've had it. Vaccines now exist to prevent HPV and the cancers it causes and are routinely recommended for children to prevent infection.
There are certain HPV-related conditions that make it more likely that you will develop anal cancer:
- History of anal warts or anal precancer: men and women with anal warts or anal precancer are at increased risk of developing anal cancer because this history indicates an HPV infection. If the infection is persistent with recurrent lesions, it can lead to changes in the anal cells, which may eventually become cancer if left untreated.
- History of other HPV-related cancer: women with a history of cervical, vulvar or vaginal cancer are at risk of developing anal cancer because these cancers are also caused by HPV, and the immune system has demonstrated difficulty in fighting the virus.
For more information on HPV and preventing the infection with vaccination see our HPV information page.
Having a weakened immune system can make the body more susceptible to developing an infection. This is also true for HPV, which can more easily develop into a persistent infection in these individuals. Individuals at increased risk of developing anal cancer include:
- HIV-positive men and women.
- Individuals with autoimmune disorders.
- Transplant recipients and other individuals on immunosuppressive drugs.
I contacted a leading doctor in the anal cancer field, who graciously spoke with me on the phone and explained his work with HPV and anal cancer. He said I likely had HPV since the ‘70’s, that had remained dormant for years, and that in the presence of severe immune suppression, probably had become carcinogenic.
Any sexual contact, including manual stimulation, has the ability to expose you to HPV. It’s important to reiterate that nearly all adults will have HPV at some point in their lifetime.
While increasing exposure will increase your chance of contracting HPV, even a person with only one lifetime partner can be infected with HPV. Having multiple sex partners can increase your chance of developing anal cancer because it can increase your chance of being exposed to a carcinogenic strain of HPV.
People who engage in anal sex are at a higher risk of developing anal cancer because they are at a higher risk of skin-to-skin contact in the anal region and contracting an anal HPV infection. Because HPV is a skin virus that is transmitted very easily, anal intimacy is not necessary to contract anal HPV or to develop anal cancer.
In addition, men who are uncircumcised are at a higher risk of developing a persistent HPV infection.
Condom use is always recommended to prevent contracting an STD. However, condom use is not completely effective at preventing HPV transmission.
Smoking increases your chances of developing anal cancer as the carcinogens (cancer-causing chemicals) in tobacco can affect the entire body. There is evidence that smoking may decrease the immune system’s ability to fight HPV infection. Studies have also shown that current smokers are at a higher risk of developing anal cancer than former smokers and those who have never smoked at all.
For help quitting smoking:
US - For help quitting visit the CDC website on smoking cessation
UK - For help quitting visit the NHS website on smoking cessation
Most cases of anal cancer are diagnosed when an individual is older than 50 years old. This is because HPV takes time to alter the cells to develop into cancer. However, there are cases of people in their 20s and 30s developing anal cancer.
If you think you are at risk of anal cancer, or are concerned you may have symptoms, see a provider to answer your questions. For more information on anal precancer and screening for it, please see our Anal Precancer page.