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AACR: The Role of Vaccines in Cancer Prevention

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The advent of cancer-preventing vaccines is exciting to many clinicians who see it as a way to stop cancer before it even starts. At AACR, vaccinology consultant Mark Kane said many people are unaware that there are a lot of cancers that have the potential to be controlled with vaccines. New ones are being developed for cervical cancer and other diseases caused by the human papillomavirus. There has also been a dramatic improvement in vaccine delivery in the developing world, and the development of public-private partnerships has provided new global financing mechanisms leading to large increases in funding, Kane added. There are still challenges, such as insufficient funding for the development of new vaccines and the anti-vaccination movement, he said, but things like the HPV vaccine to prevent cervical cancer or the hepatitis B vaccine to prevent liver cancer make a "very dramatic impact" on the world.

Ohio State University's Maura Gillison said getting vaccinated against HPV is more than just a matter of preventing cervical cancer. More recently, HPV has been implicated in — and is now thought to be a cause of — head and neck cancer. Although alcohol and tobacco use were the primary risk factors for developing head and neck cancers decades ago, the literature now shows that sexual behavior is also a risk factor, and that people orally infected with HPV16 are 15 times more likely to develop head and neck cancer than those without infection, Gillison said. Although the incidence of tobacco use has gone down in the US, rates of head and neck cancer have remained steady, and researchers believe this is because of increased sexual behavior, sexual experimentation at an earlier age, and more sexual partners over a lifetime than in years past. Recent data shows that the rates of HPV-positive head and neck cancers are increasing while the rates of HPV-negative cancers are on the decline, which correlates with a sharp decrease in smoking rates in the US.
Joel Palefsky at the University of California, San Francisco, says this type of data indicates that it is extremely important that both males and females get vaccinated against HPV. If you add up the rates of non-cervical cancer caused by HPV, there are more affected men than women — they largely develop oropharynx and anal cancers, Palefsky said. Some of these are increasing and tend to be related to sexual behavior, and are not routinely screened for in the clinic. Anal cancer rates have been on the rise in both men and women, and homosexual men are especially at risk, he added. The vaccines that prevent HPV — one effective against HPV 16 and HPV 18, and the other effective against those as well as against HPVs 6 and 11 — have been shown to be 90 percent to 100 percent effective in women who have not been exposed to those HPV types, Palefsky said. As Merck, the maker of HPV vaccine Gardasil, was looking to expand the patient population eligible to receive the vaccine, its studies found that Gardasil was also 90 percent effective against genital lesions like genital warts — also caused by HPV — in men who had never been exposed to the virus, and 65.5 percent effective in the full analysis set, which is still quite significant, Palefsky said, and similar to the efficacy shown in women. In homosexual men who had never been exposed to the virus, the vaccine was 94.9 percent effective in preventing anal cancer, and 77.7 percent effective in the full analysis set. The HPV vaccine was approved to prevent genital warts in boys ages 9 to 26, and approved to prevent anal cancer in boys 9 to 26 in December 2010, Palefsky said. He added that there is a rationale for gender-neutral vaccination for HPV: it would prevent men from spreading it to women as well as reducing the burden of disease in men by reducing rates of genital warts, anal cancer, or oropharyngial cancers. It would also protect gay men who don't benefit from female vaccination.

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