Sclerosing Epithelioid Fibrosarcoma Harboring the EWSR1 - CREB3L1 Gene Fusion: The Importance of Molecular Classification in Pediatric Sarcomas.

Background: Sclerosing epithelioid fibrosarcoma (SEF) is a very rare soft tissue sarcoma that most commonly presents in middle-aged and elderly adults but has been rarely seen in children. SEF is a very aggressive tumor with over 50% of patients experiencing local recurrence and 40% to 80% of patients experiencing distant metastatic spread. This disease has been shown to be resistant to chemotherapy and is classically treated with surgical excision.

Case: We describe the case of a 10-year-old girl with Graves' disease who presented with protruding eyes (to a greater extent on the left side) and was found to have a large mass in her left inferior rectus muscle that was diagnosed as SEF. After treatment with incomplete resection, due to the benign-appearing nature of the tumor on imaging, and proton radiation therapy, she remains disease-free at 18 months post-therapy.

Discussion: SEF is typically identified via genetic testing and recognition of the EWSR1 - CREB3L1 gene fusion as well as MUC4 expression via immunohistochemistry. DNA methylation profiling, which has traditionally been used in brain tumors, can also efficiently identify this tumor, and we recommend expanding the use of this technology for difficult to classify pediatric sarcomas.