[A case of gastric mixed neuroendocrine-non-neuroendocrine neoplasm that developed five years after pancreatic neuroendocrine tumor treatment].

We present a case of 63-year-old male patient who underwent subtotal stomach-preserving pancreaticoduodenectomy for pancreatic neuroendocrine tumor (NET) G2. He had been followed up for three years and had no signs of recurrence postoperatively. Five years after surgery, he had abdominal pain. Upper gastrointestinal endoscopy showed a gastric tumor. Laparoscopic distal gastrectomy was performed without postoperative complications. The histopathological findings of the resected specimen were consistent with mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN). The immunohistochemical characteristics of the gastric MiNEN lesion were different from those of the pancreatic NET lesion resected five years ago, suggesting that those lesions were heterochronous.