Since the 1970s, the number of tonsil cancer diagnoses in Sweden has tripled, and many are the result of human papillomavirus (HPV) infection spread through oral sex, say researchers. The cancer has typically been associated with smoking and heavy drinking.

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Among 98 patients with tonsil cancer whose tumor cells were analyzed during 2003–2007, researchers found 83 were HPV-positive. In the 1970s, only 23% of tonsil cancer cases were HPV-positive, the investigators said.

Patients with HPV-positive tonsil tumors are usually diagnosed at a younger age and are likelier to survive, studies have found. Further research will assess whether the HPV vaccines Cervarix and Gardasil protect against such cancers and malignancies in the mouth, said the study authors.

“What we’re seeing today is the result of infections that occurred roughly 20 years ago,” study coauthor Tina Dalianis, a professor of tumor virology at the Karolinska Institute, told Bloomberg News. “The prognosis is obviously better for the HPV-positive patients, but the treatment is still arduous.” However, Dalianis said people with HPV-positive tumors may not need the aggressive triple-combination therapy -- chemotherapy, radiation, and surgery -- typically prescribed for tonsil cancer.

The full report, titled “Incidence of Human Papillomavirus (HPV) Positive Tonsillar Carcinoma in Stockholm, Sweden: An Epidemic of Viral-Induced Carcinoma?” was published in the International Journal of Cancer.