Anal cancer is caused by infection with human papilloma virus (HPV), the most common sexually-transmitted pathogen in the United States. The virus also causes cervical cancer in women, and the vaccine is already approved and routinely recommended to prevent this condition. The new clinical trial suggests that the same vaccine would also protect men, and likely women, against anal cancer.
"Almost six thousand people every year in this country are diagnosed with anal cancer, and more than 700 people die from the disease," said Doctor Joel Palefsky. "What this trial showed is that those cancers and deaths could be prevented."
The trial involved a group of 602 men who have sex with men from Australia, Brazil, Canada, Croatia, Germany, Spain and the United States all of whom had at least one, but no more than five, sexual encounters and who were between the ages of 16-26 years. All were randomised into groups that either received a placebo or a three-shot injection of the vaccine Gardasil, which protects against HPV 16 and 18, the most common HPV types involved in anal cancer, and HPV 6 and 11, the most common types in anogenital warts. The patients were enrolled in the trial from 2006-2008, and they were followed for three years after their last shot.
As described in the paper, the vaccine proved effective at reducing anal infections with HPV and precancerous lesions known as high-grade anal intraepithelial neoplasia, which are anal cancer precursors. The trial showed that the vaccine reduced the incidence of these cancer precursors by nearly 75 per cent among those who had not been previously exposed 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, the vaccine reduced the incidence of the precancerous lesions by 54 per cent.
"Based on these data, the vaccine works well to prevent HPV infection and precancerous anal disease, and will likely prevent anal cancer in men," said Palefsky. "The ideal time to begin vaccination would be before initiation of sexual activity, but vaccination may also be useful after initiation of sexual activity."
MEDICA.de; Source: University of California, San Francisco (UCSF)