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Risk Factors of Anal Cancer
What Raises Your Risk for Developing Anal Cancer?
A risk factor is anything that makes it more likely a person will get a disease. Having one or more risk factors does not mean someone will definitely get anal cancer, and some people who get this cancer have no known risk factors at all. Still, learning about these factors can help you and your doctor understand your own health picture and decide if extra screening or precautions make sense for you. According to the National Cancer Institute (NCI), several things are linked to a higher chance of developing anal cancer.
The human papillomavirus (HPV): The single biggest risk factor is HPV infection. The NCI reports that about nine out of every ten anal cancer cases happen in people who have an HPV infection in the anal area. HPV is a very common virus that spreads through skin-to-skin contact, most often during sexual activity. Most people who get HPV never know it, because the body's immune system usually clears the virus on its own within a couple of years. But when certain high-risk types of HPV, especially HPV 16 and HPV 18, stay in the body for a long time, they can cause normal cells in the anal lining to slowly change and eventually become cancer.
Sexual behavior plays a large role in HPV exposure, so it also affects anal cancer risk. According to the American Cancer Society (ACS), having receptive anal intercourse, meaning being the receiving partner during anal sex, raises the risk of anal cancer in both men and women. Having many sexual partners over a lifetime also raises risk, since each new partner adds another chance to be exposed to HPV. People who have had anal warts, which are also caused by HPV, or other sexually transmitted infections tend to have a higher risk as well.
A weakened immune system: Another major risk factor is that the immune system is usually good at finding and clearing HPV before it can cause lasting damage. When the immune system is weaker than normal, HPV infections are more likely to stick around and cause cell changes. People living with HIV/AIDS have a much higher risk of anal cancer than people without HIV, and this risk is even higher in people who smoke or use intravenous drugs along with having HIV. People who have received an organ transplant and take immunosuppressive drugs to prevent organ rejection also face a higher risk, since these medicines are designed to calm down the immune system.
Smoking cigarettes: A well-documented risk factor for anal cancer. The ACS notes that current smokers are more likely to develop anal cancer than people who have never smoked or who quit in the past. The risk appears to rise with how much and how long a person has smoked. Scientists believe that chemicals in tobacco smoke may damage cells throughout the body, including in the anal area, and may also make it harder for the immune system to fight off HPV infection.
Women who have had cervical, vaginal, or vulvar cancer: Precancerous changes in those areas have a higher chance of also developing anal cancer. This connection makes sense because these cancers are usually caused by the same high-risk types of HPV. If HPV has already caused cell changes in one part of the genital area, it may also be affecting nearby tissue, including the anus.
Age: Is another important factor. Anal cancer is uncommon in people younger than 35 and becomes more common as people get older. The ACS reports that the disease is found mainly in older adults, with the highest rates seen in people age 75 and older. This pattern is common with many cancers, since it often takes many years for HPV related cell changes to progress into actual cancer.
Long-term irritation or inflammation: These conditions in the anal area, such as from chronic anal fistulas, have also been studied as a possible contributor to anal cancer in some cases, although this is a much less common pathway than HPV infection. People with ongoing digestive conditions that cause chronic inflammation, such as Crohn disease, may also have a somewhat higher risk, partly because these conditions can involve long-term tissue irritation and partly because some treatments for these conditions suppress the immune system.
It is worth noting that anal cancer affects men and women differently. According to ACS statistics, anal cancer is almost twice as common in women as in men overall, though rates are especially high among men who have sex with men. Anal cancer is also somewhat more common in White women and Black men. The ACS estimates that about 11,270 new cases of anal cancer will be diagnosed in the United States this year, and rates have been slowly rising over the past several decades, with a faster rise among women than men.
Factors That May Lower Your Risk of Anal Cancer
No single action can guarantee that a person will never get anal cancer, but there are several steps supported by the Centers for Disease Control and Prevention (CDC), the NCI, and the ACS that may lower a person's risk over time. These steps focus mostly on preventing or managing HPV infection, since HPV is the leading cause of this cancer.
Getting the HPV vaccine: One of the most important things a person can do. The vaccine used in the United States, known as Gardasil 9, protects against nine types of HPV, including HPV 16 and HPV 18, the types most often linked to anal, cervical, and other cancers. The CDC recommends that children get the HPV vaccine at age 11 or 12, though it can be given as early as age 9. People who start the vaccine series before age 15 need two doses, while those who start at age 15 or older need three doses. The CDC also notes that the vaccine works best when given before a person becomes sexually active, since it prevents new HPV infections rather than treating ones a person already has. The vaccine is approved for use up through age 45 for some adults after talking with a doctor. The CDC states that the HPV vaccine has the potential to prevent more than 90 percent of cancers caused by HPV, which strongly suggests it may lower anal cancer risk as well, since anal cancer is closely tied to the same HPV types.
Practicing safer sex: Also helps lower risk, although it cannot fully prevent HPV exposure. Because HPV spreads through skin-to-skin contact, condoms only cover part of the skin involved during sex, so the ACS explains that condoms may lower the chance of getting HPV but do not eliminate it. Still, using condoms consistently, along with having fewer sexual partners, may reduce the overall chance of HPV exposure over a lifetime. Open conversations with partners about sexual health and getting tested for sexually transmitted infections can also support lower risk.
Quitting smoking: Another meaningful step. The ACS states that stopping smoking greatly reduces the risk of developing anal cancer, along with many other cancers such as lung, throat, and bladder cancer. Because the risk connected to smoking appears to build up over time, quitting earlier in life may offer more benefit, though quitting at any age is helpful for overall health.
For people with HIV, staying on antiretroviral therapy (ART): Regular medical checkups are important. Good HIV management supports a stronger immune system, which may help the body clear HPV infections before they progress into precancerous changes. The NCI notes that treating high-grade precancerous anal lesions, sometimes called high-grade squamous intraepithelial lesions, may lower the chance that these changes turn into full anal cancer, especially in people with HIV.
Regular medical checkups matter for everyone: Not just people with HIV but people at higher risk, such as those with HIV, a history of anal warts, or a history of cervical, vaginal, or vulvar cancer, may benefit from talking with their doctor about anal Pap tests or an exam called anoscopy, which uses a lighted scope to closely check the lining of the anus for early changes. The NCI notes that anoscopy screening may help lower the risk of dying from anal cancer, particularly in people living with HIV, because it can catch precancerous changes early, when they are easiest to treat.
Maintaining a generally healthy immune system: This plays a supporting role. This includes eating a balanced diet, getting enough sleep, managing chronic health conditions with a doctor's guidance, and avoiding unnecessary immune-suppressing medications when safer alternatives exist. For people who need immunosuppressive drugs for a transplant or an autoimmune condition, working closely with a doctor to monitor for early signs of HPV related changes may help catch problems sooner.
It is important to remember that these strategies may lower risk, but they do not offer complete protection against anal cancer. Even people who are vaccinated, practice safer sex, avoid smoking, and get regular checkups can still develop this cancer, though their overall chances are generally lower. Anyone with symptoms such as unusual bleeding, pain, itching, or a lump near the anus should see a doctor promptly, since early detection generally leads to better treatment outcomes, according to the ACS.