Factors behind head and neck cancer revealed (Reuters)

WASHINGTON (Reuters) - There are two distinct culpritsbehind head and neck cancer -- the long-recognized heavytobacco and alcohol use as well as a common sexuallytransmitted virus, researchers said on Tuesday.

The risk factors are so dramatically different in head andneck cancer in people infected with the human papillomavirus,or HPV, that it should be considered a separate disease fromcases in which patients are not infected, researchers at JohnsHopkins University in Baltimore said.

Head and neck cancer includes tumors in the mouth, tongue,nose, sinuses, throat and lymph nodes in the neck.

"These are completely different cancers and we need to viewthem as such. They just happen to occur in the same place. Therisk factors didn't appear to overlap at all, and there didn'tappear to be any interaction between them," Dr. Maura Gillison,a professor of oncology and epidemiology, said in a telephoneinterview.

More than 35,000 people are diagnosed with head and neckcancer annually in the United States alone. If found early,such cancer may respond well to treatment with surgery,radiation therapy and chemotherapy.

Not only are the patient populations different inHPV-positive and HPV-negative head and neck cancer, but thetumors look different under a microscope, Gillison said. Peoplewith the viral-linked cancer also tend to respond better totreatment than those not HPV-infected, she added.

HPV is a common sexually transmitted virus. It is wellknown for causing cervical cancer and genital warts.

Since 2000, researchers have also known that HPV infectionwas linked to some cases of head and neck cancer, particularlyin the upper throat and back of the tongue.

The new study, published in the Journal of the NationalCancer Institute, focused on 240 people diagnosed with head andneck cancer between 2000 and 2006.

Nearly 40 percent of them had an HPV infection. Thosepatients did not have the well-known risk factors for head andneck cancer -- tobacco smoking, alcohol use and poor oralhygiene, the researchers found.

The people with viral-linked cancer cases had a completelydifferent set of risk factors, including certain sexualbehaviors and marijuana use, the researchers found.

Sexual behaviors linked to these patients includedincreasing numbers of lifetime sex partners including oral sex,and the presence of a sexually transmitted disease, they said.

Gillison said it is possible other behaviors linked withmarijuana use could be responsible, but said chemicals inmarijuana called cannabinoids could affect the immune system'sability to clear a viral infection.

(Editing by Maggie Fox and Todd Eastham)