Clinical and histologic aspects

Basal cell carcinomas (BCCs) are the most common human cancer, occurring in a predicted one-third of US Caucasians (1,2). Fortunately although their common occurrence makes them expensive in aggregate to treat, they metastasize only very rarely and cause morbidity generally via local invasion and damage to normal tissues. In the great majority of cases, they occur sporadically, in particular on the sun-exposed skin of older persons of Caucasian descent. Their incidence is rising, and this seems to correlate in part, but only in part, with increased exposure to UV mutagenesis. Histologically, BCC tumor cells resemble the keratinocytes of the basal layers of the inter-follicular epidermis and the outer root sheath of the hair follicles with large nuclei and relatively scant cytoplasm. Various clinical and histologic subtypes are recognized, the most common of which is the nodular variety in which the tumor is palpable, has a translucent appearance, often with a central “dell,” and typically is surmounted by visible telangectasia. Less common are more superficial BCCs with a “radial” growth pattern hugging the underside of the inter-follicular epidermis and occurring predominantly on the trunk rather than the face, and the morphea form, with smaller numbers of tumor cells embedded in a hyperplastic stroma. In general the histologic appearance of the BCC stroma differs from that of the surrounding normal stroma, and the expression pattern of the BCC stroma may differ from that of other cancers (3).