LAUSR

Low-grade fibromyxoid sarcoma, also known as Evans tumor, is a low-grade sarcoma that most commonly arises in the deep soft tissue of the proximal extremities or trunk in young adults. It is very rare in the viscera as a primary site with only a few cases reported in the literature. Here we present a case of Evans tumor occurring in an unusual and rarely reported location: the mediastinum. A 32-year-old male presented with history of persistent cough, and subsequent imaging revealed a left diaphragmatic tumor measuring around 11 cm with associated chest wall implants. Grossly, the tumor was well circumscribed, arising from the parietal pleura with attachment to both lung and diaphragm and focally involving visceral pleura with no extension into the underlying lung parenchyma. Histologically, the tumor was composed of uniform and bland-appearing spindle cells interspersed among large areas of hyalinized rosettes, so-called giant rosettes. By immunohistochemistry, the tumor was positive for EMA, bcl-2, TLE-1, and MUC-4 and negative for STAT-6, ruling out solitary fibrous tumor. FISH for SYT gene rearrangement was performed and was negative, ruling out synovial sarcoma. Given the overall morphology and the phenotype, the final diagnosis was low-grade fibromyxoid sarcoma with giant collagen rosettes (also known as hyalinizing spindle cell tumor with giant rosettes). Mediastinal low-grade fibromyxoid sarcoma is a rare entity that should be considered in the differential diagnosis of visceral soft tissue tumors. Pathologic examination and a thorough immunohistochemical and molecular workup play a vital role in establishing this rare and challenging diagnosis.