An Incidental EWSR1-Rearranged Sarcoma of the Orbit with Primitive Neuroectodermal Morphology and Myogenic Differentiation: A Case Report and Diagnostic Challenge”

Abstract Orbital and ocular space-occupying lesions comprise a spectrum ranging from common to extremely rare entities. These neoplasms may be primary or secondary. The incidence of primary malignant orbital tumors has been reported to be 10 per 10 million per year. We report an incidental case of a tumor attached to right extraocular muscle in a 40-year male who was a victim of a road traffic accident and presented with abrasions on the left side of the face following a fall from a motor vehicle. Radiological examination (MRI brain and CT brain) showed an incidental well-circumscribed tumor attached to lateral rectus muscle of the right eye measuring 3 × 2 × 1 cm. Microscopy showed a nodular tumor with prominent Homer-Wright rosettes. The tumor was immune-positive for desmin and smooth muscle actin and immune-negative for MyoD1, myogenin, CD99, WT1, pancytokeratin, epithelial membrane antigen (EMA), synaptophysin, chromogranin, CD34, glial fibrillary acidic protein, and HMB45. NKX2.2 staining was inconclusive and the MIB-1 labeling index was approximately 10 to 12% in areas of highest proliferative activity. The possibility of neuroectodermal tumors, the solid variant of alveolar rhabdomyosarcoma, neuroblastoma, PEComa, desmoplastic small round cell tumor, and metastasis from a neuroendocrine tumor was ruled out, and a diagnosis of a round cell tumor with primitive neuroectodermal tumor-like morphology and myogenic differentiation was rendered. Interphase FISH testing for EWSR1 showed an EWSR1 gene rearrangement. As the biologic potential of such tumors is unknown, complete excision has been proposed as the treatment of choice. Adjuvant chemoradiation may be considered based on the presence of residual tumor or local spread. This case represents an entity belonging to the EWSR1 family with unusual morphology and an ambiguous immunoprofile. It is a classic example of cases that cannot be diagnosed without molecular techniques and highlights the limitations we face in this era of molecularly defined entities.