Researchers have attributed the increase of head and neck cancer incidence in young adults, a group traditionally at low risk, to the human-papillomavirus (HPV), a cancer-causing virus that can be transmitted through oral sex. Many studies support that oropharyngeal cancers — those affecting the tonsils, back of the mouth (throat) and base of the tongue — have been on the rise since the mid-1980s, and currently 50-70 percent of these cases are caused by HPV infection. Many studies show that patients with HPV-positive oropharyngeal cancers are more responsive to treatment and have better survival rates than HPV-negative patients.