289 Subcutaneous TFE3 Translocation-Associated Perivascular Epithelioid Cell Neoplasm (PEComa): A Rare Manifestation

Abstract

Perivascular epithelioid cell neoplasms (PEComas) are a group of tumors composed of perivascular epithelioid cells that demonstrate both melanocytic and muscular differentiation. This family includes renal angiomyolipoma, pulmonary clear cell sugar tumor, and less common neoplasms of the soft tissue. TFE3 translocation-associated perivascular epithelioid cell neoplasm (PEComa) is a rare distinct form of PEComa, which is poorly studied due to infrequency and limited reports of confirmed cases by FISH study in the literature. To date, to the best of our knowledge, there have been only six reports of this entity in the subcutaneous area. Here, we present a 46-year-old woman with right flank subcutaneous mass. MRI showed an ill-defined 4 cm heterogeneous non-enhancing lesion in the right lumbar region with no renal abnormalities. The excised lesion had a fleshy gray cut surface. Histologically the tumor had a nested and alveolar architecture, and was composed of epithelioid cells with finely granular cytoplasm. The tumor cells were immunoreactive for cathepsin K, HMB45, and TFE3 with low Ki67 index. Immunohistochemically they were negative for Melan A, desmin, SMA, chromogranin, and RCC immunomarkers. The FISH study revealed TFE3 gene rearrangement. One-year follow-up of the patient has been negative for recurrence or metastasis. The non-renal cases of TFE3 translocation-associated PEComas are uncommon (extremely rare in subcutaneous tissue), and they present with distinctive immunophenotype and histomorphology features, including predominant alveolar architecture, epithelioid tumor cells, non-reactive tumor cells to muscle immunomarkers, and strong TFE3 immunoreactivity. The TFE3 translocation needs to be confirmed by FISH study.