ALTERED EXPRESSION OF BETA-2-MICROGLOBULIN IN BASALOID PROLIFERATIONSOVERLYING DERMATOFIBROMAS

The epidermis overlying 2-8% of dermatofibromas shows basaloid prolife rations that are indistinguishable from superficial basal cell carcino ma. It is well established that basal cell carcinomas uniformly exhibi t a strongly reduced expression of HLA class I molecules. Nineteen der matofibromas with over-lying basaloid proliferations were studied by i mmunohistochemistry using a monoclonal antibody against beta-2-microgl obulin, the invariant chain of the HLA class I molecule. The basaloid proliferations exhibited the same strong reduction in expression of be ta-2-microglobulin as demonstrated in basal cell carcinomas. We sugges t that this phenomenon may represent a proliferative change induced by the mesenchymal cells of the underlying dermatofibroma.