Atypical Presentation in Sclerosing Epithelioid Fibrosarcoma: A Case Report

Abstract Introduction/Objective Sclerosing Epithelioid Fibrosarcoma (SEF) is a rare sarcoma with characteristic EWSR1::CREB3L1 fusion and MUC4 positivity by immunohistochemistry (IHC). SEF most often presents as primary soft tissue tumor in the lower extremities. Histologically, characterized cords, nests or sheets of monotonous, epithelioid cells dense collagenous background. We report case an atypical location unique histological cytogenetic findings. Methods/Case Report A 13-year-old male presented left leg back pain. CT scan demonstrated 7.3 x 5.7 6.8 cm hemiabdomen mesenteric mass metastatic nodules pancreas, liver, L1 vertebrae sacrum. Sacral biopsy infiltrative discohesive small to medium round scant eosinophilic clear cytoplasm but without conspicuous stroma. An extensive IHC panel was positive only for CD99. Fluorescence in-situ hybridization (FISH) unusual finding variant pattern. FISH revealed EWSR1 rearrangement unidentified partner. The karyotype normal dividing utilized chromosome analysis, suggesting enriched non-dividing cell population. Next- generation sequencing (NGS) that confirmed FISH, IHC, further supporting classification SEF. Results (if Case Study enter NA) NA Conclusion Due presentation histologic appearance this sarcoma, integration NGS were required fully characterize lesion.