NCI and Indian investigators conducted a retrospective evaluation of human papillomavirus (HPV) prevalence in a case series of 150 oropharynx tumors diagnosed at three cancer hospitals in Hyderabad, India (Apollo Hospital, the Indo-American Cancer Center, and the MNJ Regional Cancer Center). HPV status was evaluated using p16 immunohistochemistry, HPV16-specific PCR, and HPV16 in situ hybridization. Results indicated that approximately 16 to 20 percent of oropharynx cancers were HPV-positive, a proportion that was significantly lower than the reported prevalence from studies conducted in the United States (approximately 70 percent). Based on these results, investigators concluded that tobacco use remains the main cause of head and neck cancers in this region.