[Basal cell carcinoma. Molecular genetics and unusual clinical features].

Basal cell carcinoma is the most common human cancer. Its incidence is steadily increasing. The development of basal cell carcinoma is linked to genetic factors, including the individual skin phototype, as well as the cumulative exposure to UVB. The vast majority of basal cell carcinomas are sporadic tumors, while familial cases associated with certain hereditary syndromes are less common. At the molecular level, basal cell carcinomas are characterized by aberrant activation of sonic hedgehog signaling, usually due to mutations either in the ptch or smoh genes. In addition, about half of the cases carry mutations in the tp53 tumor suppressor gene, which are often UVB-associated C-->T transition mutations. Clinically, basal cell carcinomas may show a high degree of phenotypical variability. In particular, tumors occurring in atypical locations, showing an unusual clinical appearance, or imitating other skin diseases may cause diagnostic problems. This review article summarizes the current state of the art concerning the etiology, predisposition and molecular genetics of basal cell carcinoma. In addition, examples of unusual clinical manifestations are illustrated.