Relationship of viral infection to malignancies.

The epidemiologic features and the biologic mechanisms of the oral tumor viruses have been clarified during the period under review. The use of more sensitive detection methods has confirmed that the prevalence of papillomaviruses in the mouth in patients with various lesions, as well as in healthy individuals, is high. Mechanisms by which papillomaviruses are regulated by cells and by which they may control cell behavior have been described. Herpes simplex virus has been shown to induce a variety of mutations in cells. Human herpesvirus type 6 has been found in oral tissues of a number of healthy individuals, and the virus was shown to be capable of transforming cells to a malignant phenotype. Hairy leukoplakia was found in other individuals who were not infected with the human immunodeficiency virus, and a new animal model for hairy leukoplakia was introduced. Because of the high frequency of oral viruses in nondiseased individuals, more attention must be paid to their mechanisms of action before it will be possible to define the role of viruses in oral malignancies.