Epidermodysplasia verruciformis: a model for understanding the oncogenicity of human papillomaviruses

The first evidence for the oncogenic potential of human papillomaviruses (HPVs) was obtained through the study of epidermodysplasia verruciformis (EV). This rare skin disease is characterized by disseminated, refractor, pityriasis versicolor-like lesions as well as flat wart-like lesions, and by the development of skin carcinomas in about 30% of the patients. EV is a multifactorial disease involving genetic, immunological and extrinsic (actinic) factors, in addition to infection with specific HPV types. A number of HPVs (at least 15 types) have been characterized in benign EV lesions. HPV DNA sequences are regularly detected in EV carcinomas but, in contrast to benign lesions, the types associated with cancers are usually restricted to HPV-5 and, less frequently, HPV-8, an HPV-5-related type. HPV-5 genomes are usually found as free monomeric or oligomeric DNA molecules in EV carcinomas, and frequently contain deletions. This is in contrast with HPV DNA sequences in genital cancers, which are often integrated into the host DNA. Evidence for the transcription of HPV-5 genomes in primary and metastatic EV carcinomas has recently been obtained. The available data indicate that HPV-5 and some HPV-5-related types have an oncogenic potential and play a role in the malignant transformation of EV lesions. Infection by these HPVs must be considered a major risk factor for the development of cancers in EV patients. EV HPV DNA sequences have only rarely been detected in premalignant or malignant lesions of the skin in the general population. This further stresses the role of genetic, immunological and extrinsic factors in the abnormal susceptibility of EV patients to a set of specific HPV types.