Extraskeletal Ewing sarcoma primarily arising in the stomach and omentum in children: a case series

Primary visceral extraskeletal Ewing sarcoma is exceedingly rare; gastric and omental primaries pose diagnostic challenges by mimicking benign gastrointestinal conditions. We present a 17-year-old with a gastric mass and a 12-year-old with an omental primary, mismanaged as iron deficiency anemia and functional constipation, respectively. Diagnoses were confirmed via imaging, endoscopy, and histopathology with EWSR1::ERG and EWSR1::FLI1 fusion detection. Both received neoadjuvant chemotherapy for cytoreduction and organ-sparing surgery. The first underwent wedge gastrectomy with positive serosal margins, lymphovascular invasion, and nodal involvement necessitating adjuvant therapy. The second, presenting with peritoneal sarcomatosis and bone marrow metastasis, underwent en bloc enterectomy, achieving 5-year disease-free survival despite toxicities requiring early discontinuation. These cases underscore radiographic-pathologic dissonance, wherein imaging regression may not reflect biological clearance, and high suspicion for small round blue cell tumors in refractory presentations. Multimodal integration of molecular diagnostics, induction chemotherapy, and aggressive cytoreduction optimizes visceral extraskeletal Ewing sarcoma outcomes.