LAUSR

A 70-year-old male presented with diplopia and painless proptosis of the left eye for 5 months. Examination showed 6 mm of axial proptosis and restriction of supraduction, abduction and adduction, and mild limitation of infraduction of the left eye. Magnetic resonance imaging demonstrated a large, moderately well-circumscribed intraconal mass in the left lateral orbit, and excisional biopsy was performed. Histopathologic features of mixed fibrous and myxoid areas in a whorl-like pattern and immunohistochemical staining for MUC4 confirmed the diagnosis of low-grade fibromyxoid sarcoma (LGFMS). Next-generation sequencing revealed genetic fusion of EWSR1-CREB3L1. LGFMS is an extremely rare neoplasm with only two prior documented cases of orbital involvement. Here, we report the third case of orbital LGFMS.