Human papillomaviruses and non-melanoma skin cancer: basic virology and clinical manifestations.

Human papillomaviruses (HPV) infect cutaneous and mucosal epithelia and induce benign and malignant lesions. Non-melanoma skin cancer (NMSC), encompassing basal cell carcinoma and squamous cell carcinoma (SCC), is the most frequent cancer in the Caucasian population, and the incidence has increased dramatically worldwide. Ultraviolet (UV) radiation is a major risk factor for NMSC, and cutaneous HPV is also considered to play an active role during the pathogenesis of these cancers. The first evidence for the involvement of HPV in NMSC was reported in patients with Epidermodysplasia verruciformis (EV). HPV types detected in skin tumours of these patients are referred to as EV/cutaneous HPV types belonging to the beta- and gamma-papillomaviruses (PV). Epidemiological studies have shown a higher risk of several EV/cutaneous HPV types for NMSC. Furthermore, in vitro and animal models show transforming properties of some PV types. The anti-apoptotic activities, and the delay of DNA repair mechanism caused by some EV/cutaneous HPV E6 proteins in response to UV-induced mutations, may lead to the persistence of DNA-damaged keratinocytes. Thus, specific EV/cutaneous HPV types as co-factors in association with UV-radiation and the immune system seem to be involved in the early pathogenesis of cutaneous SCC.