Abstract
Nonfunctional pancreatic neuroendocrine tumors (NF-pNETs) in patients with multiple endocrine neoplasia type 1 (MEN1), which results from a mutation in the MEN1 gene, are commonly small, multiple tumors located in the pancreatic head and inside the pancreatic parenchyma. We herein describe a 35-year-old woman with bone pain and a 7-year history of a prolactinoma. She was clinically diagnosed with MEN1 based on the presence of the prolactinoma and parathyroid hyperplasia. Abdominal computed tomography revealed a 5-cm mass close to the splenic hilum. This soft tissue tumor, which was located outside the pancreatic parenchyma and the tissue origin of which could not be identified preoperatively, was found to be connected to the pancreatic tail. After resection, histological examination revealed a well-differentiated neuroendocrine tumor of pancreatic origin. Genetic testing revealed a heterozygous transition mutation of guanine to adenine at the coding nucleotide 133 in exon 2 (c.133G>A), resulting in an amino acid substitution of glutamic acid with lysine (E45K) in the MEN1 gene. This patient with MEN1 presented with a clinical condition involving a single non-metastatic NF-pNET located outside the pancreatic parenchyma with a missense mutation in the MEN1 gene, which could easily have been misdiagnosed as an accessory spleen.