In reporting an increase in rectal cancer incidence among young (aged <40 years) Americans during the last quarter century, Meyer and colleagues 1 call for further investigation of risk factors, especially of interactions among environmental factors and changing population genetics resulting from the shifting demographics in the United States. In our view, candidate environmental factors should include anal sexual behaviors, especially receptive anal intercourse, that can deposit potentially immunosuppressive (eg, semen) or carcinogenic (eg, sexually transmissible pathogens) foreign antigens.
Receptive anal intercourse is associated with anal cancer. 2 Human papilloma virus (HPV), presumably transmitted through anal intercourse, is also considered the main cause of anal cancer. 2 The prevalence of anal intercourse in heterosexuals in the United States has increased during the last 20 years, 2 and the incidence of anal cancer has similarly increased for women and men in all age groups in the United States during the same period. 3 HPV infection may cause both squamous cell carcinoma (the predominant form of anal cancers) and adenocarcinoma (the predominant form of rectal cancer). HPV-associated adenocarcinomas have accounted for 20% of cervical cancer in North American women during recent years. Importantly, HPV infection is also associated with rectal adenocarcinoma. 5 Therefore, the recent increases in the prevalence of anal sex may well underlie, in part, the concurrent increases in rectal cancer in young Americans.
Assessing history and frequency of receptive anal intercourse should be a priority both at rectal cancer diagnosis and in epidemiologic research on rectal cancer. We realize that asking potentially embarrassing questions may be difficult for clinicians and cancer researchers. In our experience, asking such questions in a nonapologetic, nonjudgmental tone considerably attenuates patient-provider discomfort. When such investigations reveal an association between receptive anal intercourse and rectal cancer, then screening and prevention messages should be augmented by an additional focus on receptive anal intercourse.