Peripheral primitive neuroectodermal tumor of the stomach

Peripheral primitive neuroectodermal tumor (pPNET) is defined as small round cell sarcoma with neuroectodermal differentiation. It tends to arise in extremities, paravertebral lesions and chest wall of adolescents or young adults. This time, we present a rare case of pPNET arising in the stomach. A 68-year-old man visited our hospital with the complaint of anorexia. On endoscopy, a large tumor with ulcerative lesion was detected at cardiac lesion. Histological examination on biopsy material detected small round cells with enlarged round nuclei and scanty cytoplasm. Immunohistochemical staining was performed, but it was difficult to obtain definite diagnosis as for the histological type preoperatively. Total gastrectomy was performed, and immunohistochemical staining on resected specimen revealed that the tumor cells expressed CD99. Besides, EWS-FLI1 fusion transcript was confirmed by reverse transcription-polymerase chain reaction, which led us to the final diagnosis of tumor was pPNET arising in the stomach. The patient died 4 months after the operation due to multiple liver metastasis. Recently, the efficacy of the multidisciplinary treatment for pPNET has been reported. When we encounter a primary gastric tumor consisting of small round tumor cells, pPNET should be included in the differential diagnosis to obtain definite diagnosis before starting the treatment.