Epidermal basaloid cell hyperplasia overlying dermatofibromas.

In a series of 1117 dermatofibromas (69% women and 31% men), there were 25 cases (2.2%) with basaloid cell hyperplasia (BCH) of the overlying epidermis. This type of hyperplasia, which closely resembled a basal cell carcinoma (BCC), was predominantly seen in men (14 vs. 11 cases). To determine the nature of these BCHs, we applied a panel of 18 antibodies that are commonly used to classify epithelial proliferations on 6 cases with sufficient amounts of BCH and on 20 BCCs of various types. The number of CK20-positive Merkel cells was found to be increased in 4 cases of BCH, whereas these cells were completely absent or reduced in all BCCs. The significance of this finding must be interpreted with caution, but it must be regarded as a promising method to distinguish between reactive BCHs and neoplastic BCCs. Except for this rather subtle finding, none of the antibodies used could discriminate between the 2 conditions.