A vaccine to prevent cervical cancer offered strong protection against anal cancer in a large study of women in Costa Rica, adding to evidence that such vaccines can protect against more than just cervical cancer, U.S. researchers said on Monday.
The study, conducted by researchers at the National Institutes of Health, involved GlaxoSmithKline's Cervarix vaccine, which protects against infections triggered by strains 16 and 18 of the human papillomavirus (HPV).
"There was strong protection with the vaccine against anal infection," Dr. Aimee Kreimer of the National Cancer Institute, whose study appears in the journal Lancet Oncology, said in a telephone interview.
GlaxoSmithKline's Cervarix and Merck & Co's Gardasil protect against cervical cancer, the second most common cancer in women worldwide. But various strains of HPV also cause anal, penile, head and neck cancers.
Although rare, anal cancers have doubled in some countries in recent decades. Anal intercourse can increase the risk for anal cancers caused by HPV infections, and while there are more infections in women overall, men who have sex with men are especially vulnerable.
Kreimer's team wanted to see the how well HPV vaccines protected against this type of cancer. Her team found that rates of protection in the study were comparable with those seen in cervical HPV infections.
"We know anal HPV 16, but also 18, cause the bulk of anal cancers. We know if we remove the infection, it will greatly reduce the likelihood for the cancer," she said.
For the study, the researchers analyzed anal tissue specimens in a group of 4,210 healthy women aged 18-25 from Costa Rica. About half got the vaccine in three doses, and the other half got a placebo vaccine. The women were tested after 4 years for anal and cervical HPV 16 and 18 infections.
They found the vaccine prevented 62 percent of anal cancers and 77 percent of cervical cancers caused by HPV infection compared with rates in the general population.
In women with no likely previous exposure to HPV infection, the vaccine prevented 84 percent of anal HPV infections, a rate similar to the 89 percent rate against cervical HPV infection.
The team also found that Cervarix protected was cross-protective against other cancer-causing HPV types 31, 33 and 45.
"We're getting more bang for our buck than we realized with this vaccine," Kreimer said.
The study adds to evidence that HPV vaccines may protect against more than just cervical cancer.
Last December, the U.S. Food and Drug Administration approved Merck's Gardasil HPV vaccine for prevention of anal cancers in both men and women, based on studies showing it was effective in men who have sex with men, a group that has a higher incidence of anal cancer.
U.S. vaccine advisers have been weighing whether boys and young men should be routinely vaccinated against HPV, but some worry the vaccine is too costly to justify its use.
Currently, U.S. Centers for Disease Control and Prevention recommends HPV vaccinations for girls and women between the ages of 11 and 26. And while doctors are free to vaccinate boys and men ages 9 through 26, health officials so far have stopped short of a recommendation for routine vaccination for males.
Kreimer said she is not sure if her study adds enough evidence for broader use of the vaccine, but it does add evidence that HPV vaccination can protect women of average risk in the general population from anal cancer.
"I do think it is getting close to a tipping point, but I don't know if we are there yet," she said.
An estimated 5,300 new U.S. cases of anal cancer are diagnosed each year.