Melanocytic matricoma: A report of two cases of a new entity

Many reports exist of pigmented adnexal tumors containing dendritic melanoc ytes such as pigmented basal cell carcinomas and pigmented pilomatricomas. Correspondingly, melanocytes are a known component of the bulbs of anagen f ollicles. The phenomenon of melanization of adnexal tumors highlights the i nterrelationship between melanocytes and adnexal epithelium and may represe nt normal melanocytes colonizing a neoplastic proliferation, we report on t wo cases of a unique tumor composed of neoplastic matrical cells with a sig nificant component of melanocytes. Both cases presented as pigmented papule s in older men (66 and 80 years, forearm and pectoral region, respectively) . Histologically, these were well-defined nodular proliferations composed o f variably melanized, pleomorphic, and mitotically active matrical and supr amatrical cells forming clusters of "shadow cells." Admired with the epithe lial cells were numerous melanized dendritic melanocytes. Shadow cells expr essed keratin 13, and a subpopulation of S-100 protein-positive dendritic c ells were evident. No recurrence of any type was found after reexcisions 4 months and 2 years later. We propose the name of melanocytic matricoma for these two heretofore unreported cases of a unique neoplasm composed of matr ical cells and melanocytes recapitulating epithelial-melanocyte interaction in the follicular anagen bulb. Although their small size, circumscription and clinical course suggest a benign nature, melanocytic matricomas' cytolo gic atypia disclose the potential for malignant behavior.