The maker of the human papillomavirus (HPV) vaccine Gardasil, Merck & Co., announced Thursday it plans to ask the Food and Drug Administration next year for approval to market the vaccine for use in males.

"We are, in fact, studying Gardasil" in adolescent males and males ages 16-23, Janet Skidmore, a Merck spokesperson, said during the announcement. Doctors are concerned about men as vectors of HPV, she said. HPV can infect men and women alike, and HPV-infected men can develop genital warts and cancer, said Skidmore. Already, Gardasil has been approved for males ages 9-15 in Australia and the European Union.

Particularly among men who have sex with men (MSM), HPV is a significant cause of anal cancers, said Dr. David Rivadeneira, assistant professor of colon and rectal oncology at Stony Brook University Hospital. "It's one of the fastest-growing cancers in men," he said. "We know that particularly in HIV-infected men, there is an extremely high risk of squamous cell carcinoma of the anus, which is mediated by HPV."

Internationally, about 4,000 males are enrolled in Gardasil trials, and more are being signed up. "One part is focused on heterosexual men and the other part is focused on MSM," said Dr. Anna Giuliano, a Tampa-based Moffat Cancer Center epidemiologist and leader of one of the largest trials. "I am studying heterosexual men."

The HPV infection rate in men is higher than among women, said Giuliano. If HPV prevalence among men can be reduced, infection among women may be reduced too, she said.