Gastric Neuroendocrine Tumor With Pancreatic Acinar Cell Differentiation in the Background of Atrophic Gastritis: A Possible Variant of Type 1 ECL-Cell NET-A Case Report.

A gastric neuroendocrine tumor (NET) with pancreatic acinar cell differentiation is extremely rare. We report the case of an 87-year-old woman with a submucosal tumor in the gastric body on a background of atrophic gastritis. She also had Sjögren's syndrome. Initially 17.8 × 6.5 mm, the tumor enlarged over 10 years, leading to wedge resection. The resected mass (45 × 40 × 30 mm) was solid with a pale yellow to gray-white cut surface. Histologically, it showed trabecular or solid nests of epithelial cells with round nuclei and eosinophilic cytoplasm. Immunohistochemistry showed positivity for CKAE1/3, VMAT2, neuroendocrine markers, and pancreatic acinar markers. Ki-67 index was 11.2%. The tumor co-expressed PDX1 and ARX and showed loss of menin and ATRX. These findings support a diagnosis of gastric ECL-cell NET G2 arising in autoimmune gastritis, with secondary pancreatic acinar differentiation. This tumor may represent a variant of type 1 gastric NET.