A 54-year-old man with pancreatic head tumor had undergone pancreaticoduodenectomy and was diagnosed with pancreatic neuroendocrine tumor (P-NET) associated with sporadic multiple endocrine neoplasm type 1. Five years after the resection, P-NET recurred and liver metastases were observed. He was treated with a somatostatin analog. Eleven years after the resection, computed tomography revealed a new pancreatic hypodense and hypovascular mass adjacent to the P-NET that was diagnosed as pancreatic adenocarcinoma via endoscopic ultrasound-guided fine-needle aspiration. He underwent a total remnant pancreatectomy. Pathological examination showed that the lesion was constituted by a pancreatic ductal adenocarcinoma (PDAC) and a neuroendocrine tumor. Additionally, the invasive ductal carcinoma collided with the neuroendocrine tumor. Both PDAC and P-NET cells were observed in the collision area. We could observe the onset of PDAC during the treatment of P-NET. Moreover, we are the first to report the case of a collision of pancreatic endocrine and exocrine tumors diagnosed preoperatively.
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