* Human papillomavirus (HPV) infection: An examination of squamous cell carcinoma tumor tissues from patients in Denmark and Sweden showed a high proportion of anal cancers to be positive for the types of HPV that are also associated with high risk of cervical cancer (90% of the tumors from women, 100% of the tumors from homosexual men, and 58% of tumors from heterosexual men).[3] In another study done, high-risk types of HPV, notably HPV-16, were detected in 84 percent of anal cancer specimens examined.[4]
* Sexual activity: Having multiple sex partners or having anal sex, due to the increased risk of exposure to the HPV virus.[5] Homosexual and bisexual men are 17 times more likely to develop anal cancer than heterosexual men.[6]
* Smoking: Current smokers are several times more likely to develop anal cancer compared with nonsmokers.[5]
* Immunosuppression, which is often associated with HIV infection.[5]
* Benign anal lesions (inflammatory bowel disease (IBD),[7] hemorrhoids, fistulae or cicatrices). Inflammation resulting from benign anal lesions, such as hemorrhoids and anal fistulas, has been considered to cause a predisposition to anal cancer. [8][9]