MUM-1 Expression Differentiates Tumors in the PEComa Family From Clear Cell Sarcoma and Melanoma
ABSTRACT PEComas are mesenchymal neoplasms composed of perivascular epithelioid cells (PEC) and include a spectrum of tumors. PEComas and malignant melanoma share common morphological, immunohistochemical, and ultrastructural features, such as epithelioid cell morphology and melanocytic immunophenotype. Melanocytic markers commonly expressed in PEC tumors include HMB-45, Melan-A/MART-1, tyrosinase, microphthalmia transcription factor (MITF), and occasionally, S100. Given this morphological and immunophenotypical overlap, the differential diagnosis between a PEComa and malignant melanoma can represent a challenge. Additional diagnostic difficulty is the differentiation of melanoma and PEComa from clear cell sarcoma that is indistinguishable from melanoma based on the immunohistochemical profile. Recent studies have shown that MUM-1, a known lymphocyte marker shows positive immunostaining in nevi and melanomas, its expression in PEComas and clear cell sarcoma, however, has not been previously addressed. In this study, the authors analyzed MUM-1 expression using immunohistochemistry in PEComas (n = 8), the PEComa family members, angiomyolipomas (n = 13), and clear cell sarcomas (n = 11) and compared the staining pattern with malignant melanomas (n = 25), both primary (n = 14) and metastatic (n = 11). It was found that 92.3% of primary melanomas and 81.3% of metastatic melanomas were MUM-1 positive. In contrast, MUM-1 was only weakly positive in only 25% of PEComas and negative in all angiomyolipomas. MUM-1 expression was noted in 72.7% of clear cell sarcomas. The study demonstrated differential MUM-1 expression between PEComas and other true melanocytic tumors and suggested that the addition of MUM-1 to the usual panel of melanocyte markers could be a helpful adjunctive study to aid in the differential diagnosis between these entities.
[Show abstract] [Hide abstract]
ABSTRACT: PEComas are a family of mesenchymal neoplasms that have in common the presence of a unique cell type, the perivascular epithelioid cell (PEC). PECs uniquely exhibit a distinct immunophenotype with expression of both melanocytic, particularly HMB-45, and myogenic markers. Nasal PEComas are exceedingly rare. To date, 14 cases have been described in the literature and with the exception of 6 cases, the rest consistently lack epithelioid cells and HMB-45 expression and are best classified as nasal hamartomas or angioleiomyomas with an adipocytic component. Nasal PEComas may closely resemble malignant melanomas since both entities share many morphologic, immunohistochemical, ultrastructural and clinical features. The distinction is of paramount importance as melanomas tend to display an aggressive behaviour with associated poor outcome. Herein, we report a case of nasal PEComa in a 19 year girl, focusing on the importance of light microscopic, immunohistochemical and ultrastructural features in accurately establishing the diagnosis.Head and Neck Pathology 07/2013; DOI:10.1007/s12105-013-0470-z
The Korean Journal of Pathology 08/2014; 48(4):331-4. DOI:10.4132/KoreanJPathol.2014.48.4.331 · 0.17 Impact Factor