As with most cancers, there are multiple causes and risk factors for anal cancer. One significant correlation to note is the sexually transmitted human papillomavirus (HPV), which is a common viral infection. Roughly 85% of women and 91% of men will get HPV by the time they are 45. Detected in the majority of anal cancer cases, HPV is considered a major factor in causing anal cancer (as well as cervical cancer and cancers of the vagina, vulva, penis and throat). The HPV vaccine has been effective in reducing rates of infection and reducing rates of certain types of cancer. Other risk factors include: Having many sexual partners over a lifetimeEngaging in anal sexA history of HPV-associated cancer, including cervical, vulvar or vaginal cancerBeing over 50Being HIV-positiveSmokingTaking medications that suppress the immune system (being immunocompromised)