Cooperation between papillomavirus and chemical cofactors in oncogenesis.

Papillomaviruses have been identified as causative agents of squamous cell carcinoma in humans and other mammals, and several papillomavirus-encoded proteins have been found to possess transforming activity. However, papillomavirus infection per se appears insufficient to elicit carcinomas in the majority of cases, and other agents have been implicated as cofactors. This review presents epidemiological studies linking environmental carcinogens to papillomavirus-associated carcinoma, and evidence from experimental systems that attempt to identify the targets of carcinogens and viral oncoproteins, and the interactions of both in progression to carcinoma.