Just days after the U.S. government recommended that young men be vaccinated against human papillomavirus infection (HPV), a new study shows that such a vaccination may prevent the development of anal cancer.
The study, which was published in The New England Journal of Medicine, involved 602 men, ages 16-26 years, who have sex with men (MSM). The men got a placebo or the three-shot injection of the HPV vaccine known as Gardasil. Participants were then followed for three years after their last shot.
Gardasil is designed to protect against several “types” of HPV, including HPV types 16 and 18, which are commonly associated with anal cancer. In the study, Gardasil proved effective against these viral types by preventing people from being infected with them. Those vaccinated with Gardasil also had a 75 percent reduction in the number of precancerous lesions. For those in the study who were already exposed to one or more of the HPV cancer causing viral types the vaccine reduced the incidence of the precancerous lesions by 54 percent.
“Almost six thousand people every year in this country are diagnosed with anal cancer and more than 700 people die from the disease,” said Joel Palefsky, M.D., who directed the clinic that led study. “What this trial showed is that those cancers and deaths could be prevented.”
“A vaccine that can help prevent HPV types 16 and 18 related anal cancers, which account for approximately 80 percent of anal cancer cases, is an important tool to help prevent this disease,” added Richard M. Haupt, M.D., of Merck Research Laboratories. “These study data add to the large body of clinical trial data that support use of Gardasil in both females and males to help prevent certain HPV-related cancers and disease.”
Human papilloma virus is one of the most commonly sexually-transmitted viruses. It is generally contracted when teenagers become sexually active. The virus can cause anal cancer, as well as other cancers, including cervical cancer in women. Two vaccines, including Gardasil, are already being given to young women to prevent these cancers.
The study results suggest that the vaccine could protect women in addition to men from getting anal cancer. An under-reported fact is that more women develop anal cancer than men. Though less common than other cancers, HPV related anal cancer, along with HPV related head, throat, penile and cervical cancers, have been increasing in recent years (See sidebar: HPV and Oral Sex: A Risky Mix). Although less common than among women, anal cancer is also a problem for men who have sex with men and HIV-infected individuals. All these cancers evolve from precancerous growths associated with HPV cancer causing viral types. In theory, the vaccines should help prevent the development of all HPV related cancers specific to these cancer causing viral types.
A related study, led by Dr. Palefsky’s coauthor Dr. Anna Guiliano of the Moffitt Cancer Center, also shows that Gardasil effectively protects both heterosexual men and MSM against the viral types that cause HPV related genital warts. Other studies show the vaccine does the same for women.
With young girls already being widely vaccinated with one of the two existing HPV vaccines, the call has now gone out that young boys and young men should be vaccinated as well.
“The new study adds to the body of evidence supporting routine HPV vaccination of young males,” said Palefsky. “The ideal time to begin vaccination would be before initiation of sexual activity, but vaccination may also be useful after initiation of sexual activity.” he added.
The usefulness of vaccinating after the initiation of sexual activity it still being studied. But one reason for being optimistic over whether it will work is “herd immunity.” The idea that, overtime, as more become protected by either HPV vaccine, there will be a reduction in the population, or herd, of those infected with dangerous HPV viral types. It stands to reason that over time, older sexually active populations may then also benefit from vaccination as it will be less likely they will have been exposed to these viral types.
Doubtless with this in mind, the Department of Health and Human Services and the CDC’s Advisory Committee on Immunization Practices recently reviewed the clinical evidence on HPV vaccination, including the new anal cancer data. It then voted to change the vaccine from “recommended,” status to “routine” for boys up to the age of 21 years. : :
HPV and oral sex: A risky mix
One long-term effect of the HIV epidemic has been an oral sex free-for-all. Yet an unintended consequence of more people having oral sex has been an increase in the number of throat and head cancers. A 2007 NEJM study showed that having had oral sex with more than 6 different partners increased the risk of developing throat cancer by 3.4%. Performing oral sex with 26 or more partners further tripled that risk. That’s because having more sexual partners increases the chance of being exposed to HPV 16 and 18 — the specific viral types associated with HPV cancers. Fortunately the new vaccines protect against these viral types.
Another study, published in the Journal of Clinical Oncology, shows that oral sex may increase the risk of developing throat cancer more than smoking. The study also shows that if trends continue, by 2020, HPV related throat cancer may be more common than HPV related cervical cancer. Happily, these cancer trends should change for the better if the HPV vaccines become widely adminstered.