Human papillomaviruses and genital cancer.

Human papillomaviruses (HPVs) are epitheliotropic agents which preferentially infect either mucosal surfaces or the skin. A subset of the mucosotropic HPVs, in particular HPV types 16 and 18, are strongly linked with various forms of genital carcinomas. The great majority of these tumours carry integrated HPV DNA sequences and constitutively express two early viral genes, E6 and E7. DNA transfection studies show that these same genes can co-operate to immortalise human epithelial cells in vitro and that immortalised cells subsequently acquire a malignant phenotype through additional cellular genetic changes. Cell lines established from HPV-positive tumours also express E6 and E7, upon which continued tumour cell proliferation appears to depend. The development of molecular and serological markers specific for 'high risk' HPV types should allow the natural history of infection with these viruses, and their role in tumour development, to be better understood.