PRECURSORS TO SKIN-CANCER

Certain cutaneous lesions serve as both precursors of skin cancer and markers for increased risk. The solar or actinic keratosis serves such a role for the nonmelanoma (NMSC) forms of skin cancer (basal cell ca rcinoma and squamous cell carcinoma). Clinically, these keratoses mani fest as rough, scaly, erythematous patches on chronically sun-exposed surfaces, Conversion to squamous cell carcinoma in an individual lesio n is uncommon and has been estimated at 1 per 1000 per year, Individua ls with actinic keratoses have had sufficient chronic photodamage to p roduce skin cancer, and regular surveillance is recommended. The secon d precursor for invasive NMSC is Bowen's disease (squamous cell carcin oma in situ). Invasion of the dermis results in frank squamous cell ca rcinoma. Some types of viral warts may develop into squamous cell carc inoma. The most important precursor/marker for melanoma is the clinica lly atypical mole (CAM) or dysplastic nevus. CAMs occur in 5-10% of th e U.S. population, CAMs, under photographic follow-up, have been obser ved to evolve into cutaneous melanoma, The frequency of conversion to melanoma of any single CAM is quite low; however, in melanoma-prone fa milies, prospectively diagnosed melanomas arise in association with a histopathologically observed dysplastic nevus in more than 80% of the cases. Giant congenital melanocytic nevi have an approximately 6% life time risk of melanoma development. The risk associated with small cong enital nevi is uncertain. Lentigo maligna develop into invasive melano ma with a frequency reported in the literature ranging from 5-50%.