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CHICAGO (Reuters) - People are much more likely to survive head and neck cancer if the tumor is caused by the human papillomavirus or HPV, U.S. researchers said on Monday.That may mean that some patients will be able to undergo less toxic treatments, sparing them painful side effects from the current standard of chemotherapy and radiation.And since about 95 percent of these HPV-positive cancers are caused by strains that can be prevented by HPV vaccines, the findings may boost support for more widespread use of these prevention tools -- something policymakers, researchers and the companies have been promoting.Cervarix, made by GlaxoSmithKline, and Gardasil, made by Merck & Co, can prevent HPV, which causes cervical and other cancers and genital warts.Smaller studies have hinted that patients are more likely to survive cancers caused by HPV. The new study is the largest yet to make that link."Knowing that the tumor is associated with HPV is telling the patient that the prognosis is very good," said Dr. Kian Ang of the University of Texas M.D. Anderson Cancer Center, whose findings appear in the New England Journal of Medicine.The study also shows that when people with HPV-caused cancers smoke, they are far less likely to survive.The team studied 323 patients with advanced oropharyngeal cancer -- which starts in the throat just behind the mouth. They were treated with a combination of radiation therapy and chemotherapy. Of these, 206 had HPV-positive tumors.They found that nearly 83 percent of those with HPV-positive tumors survived, compared with 57.1 percent with HPV-negative cancer.When the team adjusted for other factors that affect survival, the team found that people who had HPV-positive cancers were 58 percent less likely to die from their cancers than people who had HPV-negative cancers.SMOKING EFFECTSThe risk of death was far greater, however, in people with HPV-positive cancers who smoked. A follow-up study presented on Monday at a meeting in Chicago of the American Society of Clinical Oncology confirmed that the more a patient smoked, the less likely he or she was to live.The team said the findings could be used to help doctors decide which treatments to use."We still recommend standard treatment, which is radiation plus chemotherapy," Ang said in a telephone interview. "Moving forward, we are starting to look into finding treatments that are less toxic."The study also suggests that vaccinating against HPV may be a way to prevent this kind of cancer, Dr. Douglas Lowy of the National Institutes of Health and Kevin Munger of Brigham and Women's Hospital in Boston wrote in the New England Journal of Medicine.The main reason the HPV vaccine was approved was to prevent cervical cancer, which kills 4,000 women a year in the United States alone. But various strains of HPV also cause disfiguring genital warts, anal and penile cancers and head and neck cancers.But Ang said more study is needed to determine how the HPV vaccine affects head and neck cancers."Theoretically, we say vaccination will work," he said.But he said the current HPV vaccines only cover four high-risk types of the HPV virus, and it is not clear if other strains of the virus may also play a role. New England Journal of Medicine, online June 7, 2010.