Track

Case Reports

Abstract

A 74-year-old female presented with a lobulated, rubbery, tan-pink mass on her right posterior-lateral thigh. She had no other contributing past medical history. A biopsy of the lesion revealed a poorly circumscribed proliferation composed of nests of large cells with atypical features encompassing irregular nuclear contours, variably hyperchromatic to vesicular chromatin, abundant clear cytoplasm, and numerous atypical mitotic figures, embedded within a sclerotic and myxoid stroma. Immunohistochemical studies demonstrated diffuse positive staining for Pan-cytokeratin and SMA, while S100, Sox 10, and HMB-45 were negative.  These findings were most consistent with a myoepithelial carcinoma. Subsequent resection of the mass demonstrated a spectrum of disparate morphologies. The lesion predominately consisted of a proliferation of basaloid cells with irregular nuclear contours and vesicular chromatin, reminiscent of infiltrative basal cell carcinoma with scattered foci of follicular differentiation. Additionally, foci of solid nests of neoplastic cells with eosinophilic to clear cytoplasm and associated pseudoglandular architecture were seen. A further component was also noted which recapitulated that seen in the original biopsy. Notably, foci of transition between the described elements were observed. Overall, the findings of the biopsy and resection specimens were considered to be most representative of a myoepithelial carcinoma with divergent differentiation, which may represent a significant proportion of heterologous elements. Myoepithelial carcinoma of soft tissue is a rare entity, and heterologous differentiation of myoepithelial carcinoma is an uncommonly described feature.