The drug, reviewed by the Vaccines and Related Biological Products Advisory Committee, is already approved as a vaccine for cervical cancer and for genital warts.
“I believe the rationale for [approving] the vaccine is there. The data is very strong, very robust,” committee member Ambrose Cheung, MD, a professor of microbiology at Dartmouth Medical School, said of the studies submitted by the company.
The FDA usually accepts the recommendation of its advisory committees, though it isn’t required to do so.
Anal cancer is a relatively rare form of cancer. It affects about 5,000 people per year in the U.S. However, the number of people being diagnosed with the disease has been growing at a rate of about 2% per year for the last three decades, according to Joel Palefsky, MD, a professor of medicine at the University of California, San Francisco, who spoke on behalf of Merck. The death rate is also increasing.
“This is a trend shown in every developing country where this type of data is collected,” Palefsky says.
Men who have sex with other men are diagnosed with anal cancer at a higher rate than any other population, but in terms of overall numbers, more women get the disease than do men. Women account for approximately 60% of all cases.
Like cervical cancer, anal cancer is strongly linked to several types of human papillomavirus (HPV) infections. The Merck vaccine has been shown to effectively prevent the development of HPV in girls and young women, thereby preventing cervical cancer. The anal cancer studies that Merck presented to the FDA showed a similar positive outcome in the prevention of HPV in men.
“Anal cancer and cervical cancer are essentially the same disease” in terms of their causes, says Palefsky.
Anal cancer in men also appears to be the same as anal cancer in women.
“We haven’t found any evidence of fundamental gender differences,” says the FDA’s Jeffrey Roberts, MD.
Those similarities were key components of the committee’s endorsement of the vaccine, because Merck only tested its effectiveness in preventing anal cancer in men.
“I support the extension of the indication and support extrapolating [the data] to females,” says committee member Lawrence Moulton, PhD, a professor at Johns Hopkins’s Bloomberg School of Public Health. “This is a two-fer. I think it’s a good one.”