Gastric mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) with pancreatic acinar differentiation: a case report

BACKGROUND: Gastric mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs) are infrequently encountered in routine practice. Some gastric neuroendocrine carcinomas (NECs) have a variety of differentiation patterns; however, pancreatic acinar differentiation in gastric NECs is rare. The molecular abnormalities of NECs with pancreatic acinar differentiation are not well understood. CASE PRESENTATION: A 67-year-old male with a gastric MiNEN with pancreatic acinar differentiation without any symptoms. The tumor consisted of two components, including both glandular and solid histological features. Although the former component was a common type of adenocarcinoma, the latter showed endocrine differentiation and expressed pancreatic acinar enzymes immunohistochemically. A positive signal with the anti-BCL10 antibody, which detects one of the pancreatic acinar enzymes, was also present specifically in the latter component. We also examined TP53 genomic mutations, DNA methylation status, and allelic imbalance (AI), which is an indicator of tumor aggressiveness. Although both components of this tumor showed no genomic mutation and a low methylation epigenotype, the frequency of AI was higher in the acinar-endocrine component than in the adenocarcinomatous component. The finding of AI indicated the progression of the conventional adenocarcinoma to an acinar-endocrine component and identified the aggressive potential of the acinar-endocrine component. CONCLUSIONS: We report a rare case of gastric MiNEN with pancreatic acinar differentiation. AI analysis revealed tumor progression and aggressiveness. In addition, the usefulness of the anti-BCL10 antibody for detecting the acinar-endocrine component was suggested.