New research offers women one more reason to get vaccinated against the human papillomavirus (HPV). In addition to lowering the risk of cervical, vulvar and vaginal cancer, the vaccine also protects against anal cancer.
It is believed that about 90 percent of anal cancer is caused by an HPV infection. Although anal cancer is rare, it has become more prevalent in recent years in the United States, nearly doubling in prevalence in the past decade. About 5,300 people are diagnosed with anal cancer each year, the majority of whom are women, according to the American Cancer Society.
"I think we can expect to see a profound reduction in anal cancer among women vaccinated," Aimée Kreimer, the lead author on the study and investigator at the National Cancer Institute, said.
"We know that screening for cervical works because rates have been plummeting, but for anal cancer, rates are on the rise and there is no official screening process for anal cancer in women. With the vaccine, we can have women getting vaccinated for cervical cancer who will get this added benefit of protection against anal cancer."
In a study of more than 4,000 women aged 18 to 25, researchers at the National Cancer Institute and the National Institutes of Health found that the HPV vaccine was protective against anal cancer in 62 percent of women. Among women who had no previous exposure to HPV infection, the rate of prevention was even higher at 84 percent. Researchers followed women for four years after the first vaccination.
"This is significant study because we are accumulating evidence that anal cancers in men and women can be prevented by HPV vaccination," Dr. Kevin Ault, associate professor of gynecology and infectious disease at Emory University School of Medicine in Atlanta, said.
Although the Food and Drug Administration approved the HPV vaccine for the prevention of anal cancer in boys and girls ages 9 to 26 in December of 2010, the focus of research at that time was in preventing anal cancer in men who have sex with men. What's exciting about this research, said Dr. Samuel Katz, professor and chairman of the department of pediatrics at the Duke University Medical Center in Durham, N.C., is that now there's evidence showing that it's preventative in women as well.
Further strengthening the findings is the study's finding that the vaccine is effective even in women 18 and older. Current recommendations suggest that girls get vaccinated as early as age 9 in order to increase the likelihood that they will be vaccinated before they become sexually active and might be exposed to HPV.
"The fact that it looked at women and not children and still found a benefit is really impressive," Dr. Erika Banks, associate professor of Clinical Obstetrics & Gynecology and Women's Health at Albert Einstein College of Medicine in New York City, said.
Because anal cancer usually occurs later in adulthood and takes years to develop, the study only tracked whether the vaccine prevented against the HPV infection that leads to anal cancer, not anal cancer itself. Because both Gardasil, the vaccine produced by Merck & Co. Inc., and Cervarix, the vaccine (used in this study) that is produced by GlaxoSmithKline, are relatively new, it will be years before the full preventative benefit is known.
Despite numerous studies showing a positive benefit of the vaccines, the number of women seeking and completing vaccination continues to lag. Concerns of side effects as well as the cumbersome three-dose schedule of the vaccine have hindered the popularity of the vaccine, with one study reporting that only 30 percent of girls and women who start getting the vaccine actually wind up getting all three necessary doses.