Risk factors for anal cancer may vary. Researchers continue to investigate the causes of anal cancer. Known risk factors that have been identified include chronic infection with high-risk types of human papillomavirus (HPV), gender and age. HPV, a collection of more than 100 viruses spread primarily by contact during vaginal, oral or anal sexual activity, is responsible for the majority of anal cancers. HPV may be asymptomatic for years, and persistent HPV infections may cause cell changes that, left untreated, may become cancer. The HPV vaccine provides protection against numerous strains of the virus, including subtypes 16 and 18, which are responsible for most HPV-related cancers.
Other common risk factors for anal cancer include:
HIV infection: People with the human immunodeficiency virus (HIV), which causes AIDS, are more likely to get anal cancer.
Anal intercourse: Men and women with a history of receptive anal intercourse, especially those younger than 30, have a higher risk of anal cancer.
Some gynecologic cancers: Women with a history of cervical, vulvar or vaginal cancer, which are also are caused by HPV infection, have an increased anal cancer risk.
Lowered immunity: Having a compromised immune system also means an increased risk of anal cancer. For example, people who have had an organ transplant and take medicines to suppress their immune system.
Chronic local inflammation: Those with anal fistulas or open wounds that last a long time, have a slightly higher risk for developing anal cancer.
Age: Two-thirds of anal cancer cases occur in people older than 55.
Smoking: Smokers have a significantly higher risk of anal cancer. The risk greatly decreases when smokers quit.
Race and gender: Incidence of anal cancer is higher among African Americans, particularly men, than in whites. Women are also at greater risk than men for the disease.
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