Background: Anal cancer incidence is gradually increasing. The cause of this increase is not exactly known. This systematic literature review aimed to investigate the trend in time of anal cancer incidence and to find an explanation for the supposed increase. Methods: The TRIP database and PubMed were searched for trends in time in incidence of anal cancer in the general population, for risk factors and risk groups for anal cancer, and for incidence trends in time in these risk groups. Results: Age-adjusted incidence rates have increased in all Western countries during the last decades, up to 2.2% per year. Infection with the oncogenic human papilloma virus is the most important aetiological factor. Besides increasing age, other risk factors have been identified: smoking, sexual practices, in particular receptive anal intercourse, and being human immunodeficiency virus (HIV) positive. The standardised incidence ratio (SIR) is significantly increased in HIV-positive men who have sex with men (MSM) (SIR 77.8), organ transplant recipients (SIR approx. 6) and women with a history of cervical cancer (SIR 6) or cervical intraepithelial neoplasia (SIR 16). Absolute numbers of HIV-positive MSM and organ transplant recipients have increased significantly in the last decades. Conclusion: The increasing incidence of anal cancer can be partially explained by an increase in the incidence rate in and absolute number of the most important risk group: HIV-positive MSM. The increasing number of renal transplant recipients probably also contributes. Further studies should answer the question whether these risk groups would benefit from preventive screening for anal cancer.
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