Mixed neuroendocrine non-neuroendocrine neoplasm: a case report and review.

Mixed neuroendocrine non-neuroendocrine neoplasm (MiNEN) of the pancreas is a rare entity, and obtaining a preoperative diagnosis is difficult. We present a 70-year-old man in whom the possibility of MiNEN was successfully discovered preoperatively by endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA). Immunostaining revealed positive results for the neuroendocrine markers chromogranin A and synaptophysin. We considered the possibility for MiNEN before surgery. He underwent distal pancreatectomy with splenectomy. Immunohistochemical examination of the tumor cells showed a wide range of positivity for trypsin as well as for chromogranin A and synaptophysin. Considering that ≥ 30% tumors ware positive for both acinar and neuroendocrine markers, the patient was diagnosed with MiNEN. MiNEN is a malignant tumor that requires early detection and treatment but is a rare disease for which no method has been established. We found that EUS-FNA and immunostaining are effective diagnostic methods for MiNEN.