Cutaneous clear cell myomelanocytic tumour: a new member of the growing family of perivascular epithelioid cell tumours (PEComas). Clinicopathological and immunohistochemical analysis of seven cases

Abstract

To analyse seven cases of cutaneous myomelanocytic tumour histologically and immunohistochemically. Perivascular epithelioid cell tumours (so-called PEComas) are rare and recently delineated neoplasms occurring in the lung, kidney, pancreas, uterus, falciform ligament, vulva, heart, prostate and soft tissues. PEComas are characterized by a perivascular location of neoplastic cells showing a broad spectrum of epithelioid and spindled cells with clear, and granular pale eosinophilic cytoplasm, and a variable expression of melanocytic and muscle markers, whereas S100 protein and cytokeratins are usually absent. We report seven cases of cutaneous myomelanocytic tumour arising on the lower (six cases) and upper (one case) extremities of female adults (age range 30-66 years). In all cases an ill-defined dermal lesion with extension into subcutaneous tissue was noted. The neoplasms contained numerous blood vessels with a lace-like pattern and slightly thickened vessel walls, and were composed of perivascular epithelioid cells containing clear or focally granular pale eosinophilic cytoplasm and round vesicular nuclei with small, sometimes slightly enlarged nucleoli. Increased proliferative activity and tumour necrosis were not seen. Immunohistochemically, tumour cells stained positively for HMB-45, microphthalmia transcription factor, and NKIC3 in all cases, whereas perivascular expression of alpha-smooth muscle actin and focal positivity for desmin were noted in one case each only. Two out of four cases tested stained focally positive for calponin. No expression of S100 protein and pancytokeratin was present. Despite incomplete/marginal excision in three cases none of the neoplasms has recurred locally so far. With the presented series of cutaneous myomelanocytic tumours the clinicopathological spectrum of PEComas is expanded.