Pigmented clear cell acanthoma.

We present five cases of macroscopically pigmented clear cell acanthomas. Masson-Fontana silver stain revealed dendritic melanocytes containing melanin granules in large numbers interspersed among the tumoral keratinocytes. The dendritic cells expressed S-100 protein. Electromicroscopy, performed on one pigmented clear cell acanthoma, showed melanosomes in large numbers in the dendrites of melanocytes; whereas only a few melanosomes were found in the adjacent keratinocytes, indicating a disturbed melanin transfer. We propose the name "pigmented clear cell acanthoma" for this variant of Degos' acanthoma.