Gastrointestinal: Multi-modality imaging of extraskeletal Ewing sarcoma of the stomach.

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A previously healthy 24-year-old man presented with 6-month progressive abdominal pain, nausea, vomiting, gastroesophageal reflux, changes in bowel habits, night sweats, and 12-lb weight loss. Initial Fluorine-18 fluoro-desoxy-glucose positron emission tomography/computed tomography (PET/CT) and magnetic resonance imaging revealed a large 10 × 8 × 9-cm exophytic gastric mass with tracer avidity, arising from the posterior aspect of the stomach (Fig. 1a–c). The imaging differential diagnoses included gastrointestinal stromal tumor, lymphoma, and rhabdomyosarcoma. Endoscopy and biopsy of the gastric lesion subsequently showed an extraskeletal Ewing sarcoma (EES) with tumor cells positivity for keratin OSCAR, keratin AE1/AE3, CD99, and focally positive for synaptophysin (Fig. 1d). The patient was treated with vincristine, doxorubicin, and cyclophosphamide, alternating with ifosfamide and etoposide resulting in tumor decreasing in size and resolving uptake on subsequent PET/CT restaging. The patient then underwent distal gastrectomy with confirmation of an EES. Extraskeletal Ewing sarcoma is a rare, aggressive soft tissue malignancy, occurring in children and young adults, with 85% of cases between age of 20 months and 30 years. It belongs to the Ewing sarcoma family of tumors, which represents a group of high-grade small round blue cell tumors and includes the Ewing sarcoma of the bone, EES, primitive neuroectodermal tumor, and Askin tumor (thoracopulmonary primitive neuroectodermal tumor). EES, only 15–20% of Ewing sarcoma family of tumors, affects slightly older children and young adults than Ewing sarcoma of the bone by 5–10 years, with an average age of 20 years. ESS is thought to have equal sex predilection—unlike Ewing sarcoma of the bone, which has slight male predilection of 1.5:1. EES may be ubiquitous in the body, most commonly at the paravertebral region, lower extremities, chest wall, retroperitoneum, and pelvis with other lesser frequent sites at the breast, gastrointestinal tract, prostate, endometrium, brain, and lung. Gastric EES is very rare, with only a handful of cases reported in the literature. Local recurrence is high, up to 85–90%. The 5-year survival ranges from 35–71% to 0–34%, depending on the site of occurrence and the presence of metastasis on presentation. Metastases usually target the lung and bone, with bone metastasis a poor prognosis. EES imaging is nonspecific with fluorine-18 fluoro-desoxy-glucose PET/CT showing a hypermetabolic lesion, and CT and magnetic resonance typically demonstrating an enhancing mass, with possible central necrosis and hemorrhage. Calcifications can be seen in up to 25% of cases.