Basal cell and squamous cell carcinomas. Clinico-histological features.

Basal cell and squamous cell carcinomas are the most common skin cancers, occurring mainly on sun-damaged skin of old persons. Basal cell carcinoma is a neoplasm of follicular germinative cells which may infiltrate and destroy adjacent tissues, but rarely metastasizes. Five clinico-pathologic types of basal cell carcinomas can be recognized, namely, nodulo-ulcerative, superficial, morpheiform, fibroepithelial, and infundibulo-cystic. Actinic keratosis and Bowen's disease are intrepidermal proliferation of atypical keratinocytes that eventually may progress to become over squamous cell carcinoma. Lesions arising in sites of chronic injury or scarring bear an higher risk of metastases. Keratoacanthoma is a rapidly evolving tumor of keratinocytes that resolves spontaneously. Keratoacanthoma might represent a self-healing type of squamous cell carcinoma.