Updated: 2 March 2005

The strongest risk factor for squamous cell carcinoma of the anus is the presence or history of human papilloma virus infection (HPV). Patients may also give a history of genital condyloma acuminatum. The serotype associated with anal cancer is HPV 16¹ which generally does not cause condylomata, however co-infection with several HPV strains is common. Immune suppression, including HIV infection and post-transplantation immunosuppressive therapy, facilitates chronic activation of HPV and is therefore associated with an increased risk of anal cancer. The incidence is high in homosexual males regardless of HIV status, however the incidence is not higher in HIV positive patients who do not practice anal receptive intercourse. An HIV test should be considered in all patients who may be at high risk of contracting the HIV. A positive test may have implications in terms of treatment: opportunistic infections, toxicities. Women with a history of cervix cancer, which is also strongly associated with HPV infection, are at slightly increased risk for anal cancer. A controlled trial has shown a decrease in the incidence of HPV 16 after vaccination which offers hope that immunization may decrease the risk of HPV related diseases including anal canal cancer in high risk individuals².

Case-control studies have shown that cigarette smoking was associated with a significant risk of anal cancer.³

Although it was previously believed that chronic anal irritation was associated with squamous anal cancer, large case control series in patients with Crohn's disease (who have chronic anal fistulas and fissures) have not shown an increased incidence over the baseline population risk.

References:

1. Palmer JG, Scholefield JH, Coates PJ, et al. Anal cancer and human papillomaviruses. Diseases Colon Rectum 1989; 32: 1016-1022.
2. Koutsky LA, Ault KA, Wheeler CM, et al. A controlled trial of a human papillomavirus type 16 vaccine. NEJM 2002; 347: 1645-51.
3. Holly EA, Whittemore AS, Aston DA et al. Anal cancer incidence: genital warts, anal fissure or fistula, hemorrhoids, and smoking. J Natl Cancer Inst 1989; 81(22): 1726-31.