Peripheral primitive neuroectodermal tumor of the stomach in a 14-year-old boy: a case report.

Purpose Peripheral primitive neuroectodermal tumours (PNETs) are rare and highly aggressive soft-tissue malignancies originating from the neural crest. As yet, a gastric PNET has not been reported. Here, we present the case of a 14-year-old boy in whom we detected a large polypoid submucosal gastric tumour as a cause of severe anaemia and weight loss. Methods Histology, immunocytochemistry and molecular pathology were the basis to establish the diagnosis of PNET. Gastroendosonography, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and somatostatin receptor scintigraphy were performed for staging. Results In biopsy samples, small round blue tumour cells were detected clearly expressing CD99, CD117 (c-kit), S100, neurofilament, and neuron-specific enolase. The diagnosis of a PNET was confirmed by detection of the characteristic EWS/FLI-1 fusion gene, resulting in a reciprocal translocation t(11;22)(q24;q12). Three distinct liver metastases were detected by CT, MRI, and PET. The tumour failed to respond to neoadjuvant polychemotherapy with vincristine, etoposide, doxorubicin, and ifosfamide. Subtotal gastrectomy was performed and, surprisingly, we found diffuse metastatic infiltration of the liver that had not been detected by preoperative staging. Due to the diffuse metastatic disease the young patient's prognosis has to be considered very poor. Because of the tumour's intense expression of CD117 (c-kit), the patient is now treated with the tyrosine kinase inhibitor imatinib (STI571). Conclusion Although PNETs are rare malignancies, they should be considered in the differential diagnosis of submucosal gastric tumours in adolescents with clinical alarm symptoms.