Human papillomavirus infections in skin cancers.

Non-melanoma skin cancer (NMSC) is the most frequent cancer among Caucasians worldwide. The lesions occur preferentially on sun-exposed sites of the body. The role of human papillomavirus (HPV) in the etiology of carcinoma of the genital tract is well established. Epidermodysplasia verruciformis (EV) has been regarded as a model for NMSC developing on sun-exposed sites. Infection with a specific group of HPV types has been associated with the benign and malignant lesions occurring in these patients. Recent studies using improved detection methods, as well as re-examining material used in previously published studies, reported the presence of HPV DNA in NMSC from immunocompetent patients, as well as more than 90% of NMSC occurring in organ transplant recipients. Five HPV types were identified as the most prevalent in these tumors, i.e., HPV 20, HPV 23, HPV 38 and two newly identified HPV types, DL40 and DL267. These and other HPV types were also demonstrated in normal skin biopsies (35%) and a small number of melanomas. The frequent presence of more than one HPV type within a lesion was noticeable, with at least one type belonging to the EV-associated HPV types. Present data indicate that the primary infection with the majority of, if not all, HPV types, apparently occurs early in life, after which it remains latent. Prolonged ultraviolet (UV) radiation is needed either to activate viral gene functions, and/or to inactivate cellular genes responsible for controlled cell growth. Further studies are clearly needed to determine the molecular mechanisms by which these HPV infections in combination with UV-radiation may contribute to this carcinogenic process.