Clinical Trial Shows Potential Benefit of HPV Vaccine for Anal Cancer
A vaccine used to prevent viral infections that cause cervical cancer also prevents similar infections of the anus that could eventually lead to anal cancer. The vaccine, Cervarix, protects women against infection with the two types of human papillomavirus (HPV) that cause the majority of anal and cervical cancers—types 16 and 18.
The study was the first to assess the effectiveness of an HPV vaccine against anal HPV infection in women. Dr. Aimée Kreimer of NCI’s Division of Cancer Epidemiology and Genetics (DCEG) and her colleagues reported their findings online August 22 in Lancet Oncology.
“This study gives us our first indication that Cervarix provides excellent protection against two HPV types that cause anal cancer and also possibly other [HPV] types,” said Dr. Diane Harper of the University of Missouri-Kansas City School of Medicine, who was involved in clinical trials for both Cervarix and the second HPV vaccine, Gardasil.
Anal cancer is rare, but the incidence of the disease has been increasing in the United States and several European countries. Women are more likely than men to develop anal cancer; most affected individuals are diagnosed in their 60s.
To assess the vaccine’s ability to prevent anal HPV infections that could lead to cancer, the researchers tested samples from women participating in the Costa Rica HPV Vaccine Trial, a clinical trial of Cervarix to prevent cervical HPV infection, who agreed to have an anal specimen collected 4 years after vaccination. (All participants were screened for cervical HPV infections prior to vaccination and 4 years later.)
Women who did not show evidence of HPV in the cervix at the start of the trial were considered unlikely to have had anal HPV infections as well. Four years after vaccination, the rate of anal HPV infections was nearly 84 percent lower in women who received Cervarix than in women in the control group.
The level of protection against anal cancer was similar to that observed against cervical HPV infections in the trial. HPV vaccination for the prevention of cervical cancer may have the additional benefit of reducing anal HPV infections that could lead to cancer, noted Dr. Kreimer.
—Dr. Diane Harper
“Since our data show a reduction of anal HPV infection rates in vaccinated women, it suggests that, in the future, women who receive the prophylactic HPV vaccines before exposure to the virus will possibly have less anal cancer,” the study authors wrote.
Cervarix is approved by the Food and Drug Administration (FDA) to prevent cervical cancer and precancerous lesions in girls and women ages 10 to 25.
Last December, the FDA approved Gardasil for the prevention of anal cancer in both males and females ages 9 to 26. (Gardasil protects against infection with HPV types 6 and 11, which cause approximately 90 percent of genital warts, as well as HPV types 16 and 18.)
The current study also showed that Cervarix offered protection against infection with several HPV types not targeted in the original formulation—types 31, 33, and 45. This was the first time that an HPV vaccine was shown to have “cross-protection” at a site outside the cervix, noted Dr. Harper, who co-wrote an accompanying editorial with her colleague Dr. Stephen Vierthaler.
HPV infection can also cause cancers of the vagina, vulva, and penis, and some head and neck (oropharyngeal) cancers. With the exception of screening for cervical cell changes to prevent cervical cancer, there are currently no effective preventive measures for HPV-induced cancers.
“In developing countries where cervical screening programs do not exist or may not be effective, the burden of cervical cancer is far greater than that of all other HPV-associated cancers combined,” said Dr. Allan Hildesheim of DCEG, who co-led the study. In these countries, the focus of HPV vaccination programs should remain on women and on cervical cancer, he added.
The duration of protection from HPV infection with the vaccines remains a big question, noted Dr. Harper. “If the protection lasts less than 15 years, cancers will likely be delayed rather than prevented,” she said.
Because the Costa Rican trial tested anal HPV infection only once, future studies will need to evaluate the vaccine’s efficacy against persistent anal HPV infections and associated lesions, the researchers said.
In the current trial, researchers offered the HPV vaccine to women in the control group at the end of 4 years. “We are transitioning into long-term follow-up and will eventually have 10 years of data,” Dr. Kreimer said.
Further reading: NCI Fact Sheet: Human Papillomavirus Vaccines