A quadrivalent human papillomavirus (HPV) vaccine to prevent anal cancer was shown to be safe and effective in a trial of healthy men who have sex with men. The research was funded by Merck & Co, which manufactures Gardasil, the quadrivalent HPV vaccine for types 6, 11, 16, 18 used in the project. HPV 16 and 18 are the most common HPV types involved in anal cancer; HPV 6 and 11 are the most common types involved in anogenital warts.

In a substudy of a larger double-blind study conducted in the United States, Australia, Brazil, Canada, Croatia, Germany, and Spain, 602 men (aged 16 to 26 years) who had had no more than five sexual partners were randomized to a three-shot injection of Gardasil or placebo. The participants were followed for 3 years following the final shot. The primary efficacy objective was prevention of anal intraepithelial neoplasia (a precursor to anal cancer) or anal cancer related to infection with HPV 6, 11, 16, or 18.

Use of the vaccine reduced the rates of anal intraepithelial neoplasia, including grades 2 or 3, by 74.9% among men who had had no previous exposure to any of the HPV types in the vaccine. Among those who were previously exposed to one or more of the types in the vaccine, incidence of precancerous lesions fell by 54.2%. No serious adverse events related to vaccine use were reported.

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In a statement issued by the University of California–San Francisco (UCSF) to announce the study results, which were published in The New England Journal of Medicine (2011;365:1576-1585), Joel Palefsky, MD, FRCPC—founder and director of the Anal Neoplasia Clinic at the UCSF Helen Diller Family Comprehensive Cancer Center and leader of the study—noted that the ideal time to begin vaccination would be before the initiation of sexual activity, but that it may also be useful after.