A vaccine against the sexually transmitted disease HPV, which can cause cervical cancer in women, has also been shown to prevent most anal pre-cancers in gay men, an international study said.
Men who were vaccinated against human papillomavirus developed 75% fewer anal lesions that lead to cancer than their counterparts who were given a placebo, said the study in The New England Journal of Medicine.
The findings were released one day after a US advisory panel urged the Centres for Disease Control and Prevention to recommend routine vaccinations for boys age 11-12 against HPV.
The disease infects at least half of all sexually active adults and can cause genital warts, but often people with HPV show no symptoms at all.
Vaccination before sex
If caught early, the lesions caused by four particularly virulent strains of the virus can often be removed, preventing cancer from forming. But experts say vaccinating against it before people start to have sex is crucial.
There are nearly 6,000 cases of anal cancer diagnosed annually in the United States, and close to 800 deaths, according to US government health statistics.
"What this trial showed is that those cancers and deaths could be prevented," said lead author Joel Palefsky, a professor at University of California San Francisco and director of UCSF's Anal Neoplasia Clinic.
A total of 602 sexually active gay men aged 16-26 from Australia, Brazil, Canada, Croatia, Germany, Spain and the United States were included in the research.
Funded by Merck
Those in the study, which was funded by Merck, had had at least one but no more than five sexual encounters. They were randomly assigned either a placebo or a three-shot injection of Gardasil, a Merck-made vaccine.
Gardasil is the only vaccine on the market to protect against HPV 6, 11, 16 and 18 in boys and girls. A vaccine made by GlaxoSmithKline, called Cervarix, is approved for use in girls against HPV types 16 and 18.
The trial ran from 2006 to 2008 and included three years of follow up, after which those who had never been exposed to HPV showed a 75% lower rate of anal HPV infections and precancerous anal lesions.
Those exposed to one or more of the HPV types that Gardasil aims to prevent saw 545 fewer lesions than those who were not given the vaccine.
Vaccine works well
"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."
A majority of HIV-positive men in the United States are also infected with HPV, and anal cancer incidence is rising in both men and women, Palefsky said.
There are about nine new cases of cervical cancer per 100,000 women each year in the US, compared to about 100 new cases of anal cancer in HIV-positive men per 100,000 individuals.
HPV linked to other cancers
HPV is linked to almost 13,000 cases of cervical cancer yearly in US women, 4,300 of which are fatal, and is also suspected to be linked to a rise in head and neck cancers due to its transmission during oral sex.
Merck's Gardasil was approved for girls and women from age nine to 26 in June 2006 and for males in the same age range in October 2009. GlaxoSmithKline's vaccine, Cervarix, was approved in 2009 for women aged 10-25.
The CDC's Advisory Committee on Immunization Practices called for the HPV vaccine to be administered routinely to boys and men age nine to 21 before they start having sex.
The CDC is expected to accept the recommendation and issue a formal announcement within two months.
(Sapa, October 2011)