Human papillomaviruses.

During the past 17 years 73 genotypes of human pathogenic papillomaviruses (HPV) have been identified. Most of them are found in benign proliferations; however, several have been discovered in malignant tumors. Specifically, cancer of the cervix, other anogenital cancers, but also some cancers of the skin, the oral and nasal cavity, and the rare periungual carcinomas have been linked to specific HPV infections. The pathogenesis of cancer of the cervix has been particularly well studied. Specific viral genes (E6 and E7) of high risk HPVs (types 16, 18, and others) act as oncogenes. Their expression emerges as necessary but not sufficient factors for malignant conversion. Besides stimulating cell proliferation, they are responsible for the genetic instability of the infected cells. Their transcriptional and functional activity is regulated by host cell genes. Mutational modifications of the latter appear to be required for malignant progression.