Risk factors for anal cancer: results of a population-based case-control study

Objective: Although the incidence of anal cancer is higher in women than in men, the reasons for this gender difference are not clear. The purpose of this study was to identify risk factors for anal cancer in both men and women. Methods: We conducted in-person interviews with 102 males and 106 females with squamous or transitional cell carcinoma of the anus and 208 individually matched controls. Results: Compared with persons who had never experienced receptive anal intercourse, those who had experienced it more than 130 times were 18 times as likely to develop anal cancer (adjusted odds ratio [OR] = 17.6 (95% confidence interval [CI] = 1.3-234). This elevated risk occurred primarily among males. The adjusted OR for males having more than 10% of their sexual experiences with other men was 5.6 (95% CI = 1.4-22.0). A history of other anogenital or endometrial cancers increased the risk in women but not men. A history of anal warts, syphilis, severe hemorrhoids, physical inactivity, multiple sexual partners who smoked, and current smoking were also associated with increased risk. Conclusions: The results of this study suggest that both sexual and non-sexual factors are important in the etiology of anal cancer.