Where Pigmented Pilomatricoma and Melanocytic Matricoma Collide

Abstract

Pilomatricoma and matricoma are 2 benign epithelial tumours derived from the hair matrix. Although containing the same constituent cells, the silhouette differs, with matricoma comprised of a predominantly solid basaloid proliferation with only focal areas of shadow cell formation. The recently described melanocytic matricoma appears to be a similar tumor with numerous interspersed melanocytes. We studied retrospectively 28 pilomatricomas and 2 pilomatrical carcinomas to check for the presence of melanocytes using immunohistochemical staining to S-100 and Melan-A. Three cases of pilomatricoma with prominent melanocytic hyperplasia were detected, confirming this as a rare (11%) occurrence. Both cases of pilomatrical carcinoma were negative. Comparison of these tumors with a further case of melanocytic matricoma led to a critical analysis of the relationship of pilomatricoma, matricoma, and melanocytic matricoma. Although further comparison is required, we suggest that melanocytic matricoma may be simply a pigmented melanocytic variant of matricoma, in the same way as we accept pigmented pilomatricoma as a variant of pilomatricoma. In this report we provide features that may be used to discriminate matricoma and pilomatricoma and their pigmented variants.