The tumor shown here was removed by radical cystectomy from a 72-year-old man. The tumor cells stained positive for cytokeratin 7 and weakly positive for CD138, but negative for immunoglobulins and mucins. What is the most likely diagnosis?
A Urothelial carcinoma B Adenocarcinoma of urachal origin C Plasmacytoma D Plasmacytoid carcinoma E Metastatic breast carcinoma
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Answer to last month’s Case of the Month… C: Malignant perivascular epithelioid cell tumor (PEComa) PEComas are soft tissue tumors composed of nests of clear or granular eosinophilic cells that have the immunohistochemical features of perivascular epithelioid cells. These cells may be epithelioid- or spindle-shaped. The tumor nests are typically surrounded by capillary vessels. Typical PEComas may show occasional pleomorphism, but mitotic figures are usually rare or absent. Malignant PEComas are characterized by brisk mitotic activity, necrosis, marked nuclear atypia, and significant pleomorphism as in this case. Tumor cells are positive for melanoma markers, such as microphthalmia transcription factor, Melan A, and HMB45, and smooth muscle cell markers, such as smooth muscle actin or calponin. Desmin and S100 are less often positive (1). Submitted by Wei Cui, The University of Kansas School of Medicine, Kansas City, Kansas, USA. Reference 1. JL Hornick, CC Pan, “PEComas”, WHO classification of tumours of soft tissue and bone. IARC Press: 2013.
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