Primary cutaneous pecoma: a case report

Abstract

Introduction Perivascular epithelioid cell tumour (PEComa) of skin is a rare tumour. In contrast to more common presentations of PEComa, primary cutaneous PEComa appears not to be associated with tuberous sclerosis and its related tumours. Here, we present a case of primary cutaneous PEComa and discuss the differential diagnosis. Case report A 61-year-old female presented with a solitary non-tender nodule on her right knee slowly growing over 3 months. Excisional biopsy showed a pale orange-coloured firm nodule 12 × 7 mm. Microscopic examination revealed a dermal infiltrate composed of plump epithelioid cells with vacuolated to pale granular eosinophilic cytoplasm, round to oval nuclei and prominent nucleoli. Scattered amongst tumour cells, there were small aggregates of chronic inflammatory cells and occasional multinucleate giant cells as well as a delicate network of capillary-sized vessels. Mitoses, necrosis and pleomorphism were not present. Special stains showed no alcohol or acid-fast bacilli. PAS stain revealed glycogen within the cytoplasm of the epithelioid cells. Immuno-histochemistry showed strong positivity for HMB45, CD10 and CD68, and negative staining for S100, Melan A and CD34 in the tumour cells. Discussion To date, there are approximately 23 cases of primary cutaneous PEComa in English literature have been reported. 1,2,3 None of the cases had tuberous sclerosis. 2 Primary cutaneous PEComas have shown benign biological behavior, although reported cases of deep subcutaneous or non-cutaneous involvement may exhibit malignant behaviour. 2 There are a number of benign and malignant lesions in the differential diagnosis of a cutaneous PEComa; for instance, dermatofibroma with clear cell change, xanthomatous lesions, granular cell tumours, balloon cell naevus and melanoma, clear cell sarcoma of tendons and aponeuroses, and metastatic renal cell carcinoma. PEComas show a unique immunohistochemical profile with positivity for melanocytic (the most sensitive: HMB45, 100%) and smooth muscle markers (the most sensitive: desmin, 50%). 1,2 Of note, primary cutaneous PEComa is negative for S100 in contrast to PEComas in other sites which show up to 33% positivity for this marker. 1 CD68 has been shown to react with tumour cells in some of the published cases of skin PEComa; 2 whereas, CD10 status of this tumour, to our knowledge, has not been clarified in the English literature yet.