Objective: To describe the histopathological characteristics and evaluate the immunohistochemical expression of Synaptophysin, Chromogranin A, and S100 in pancreatic neuroendocrine neoplasms (PanNENs).
Methods: This cross-sectional descriptive study included 68 cases of pancreatic neuroendocrine neoplasms diagnosed at the Department of Pathology and Cytology, Bach Mai Hospital, and the Department of Pathology and Molecular Biology, K Hospital (Tan Trieu Campus), between January 2021 and June 2026. Histopathological classification was performed according to the 2022 World Health Organization (WHO) Classification of Endocrine and Neuroendocrine Tumours. Immunohistochemical staining for Synaptophysin, Chromogranin A, and S100 was performed in all cases.
Results: The mean patient age was 53.7 ± 14.3 years, and 75.0% of patients were female. NET G1 was the most common histological subtype (58.8%), followed by NET G2 (32.4%). Trabecular and nested growth patterns were the predominant histological architectures. Synaptophysin was positive in all cases, with strong expression observed in 94.1%. Chromogranin A was positive in 95.6% of cases, predominantly showing strong expression (77.9%). S100 was positive in 61.8% of cases, including strong expression in 33.8%, and was mainly observed in well-differentiated neuroendocrine tumors, whereas expression was uncommon in neuroendocrine carcinomas.
Conclusions: NET G1 was the most common histopathological subtype, followed by NET G2. Trabecular and nested growth patterns were the most frequently observed histological architectures in well-differentiated pancreatic neuroendocrine tumors (PanNETs). A solid growth pattern was identified in both PanNETs and neuroendocrine carcinomas (NECs), with higher proportions observed in higher-grade tumors in this study. Synaptophysin, Chromogranin A, and S100 expression was observed in 100%, 95.6%, and 61.8% of pancreatic neuroendocrine neoplasms, respectively. S100 expression was predominantly detected in well-differentiated PanNETs, whereas no S100 expression was observed in the NEC cases included in this study. These findings contribute to the characterization of the histopathological features and immunohistochemical expression patterns of Synaptophysin, Chromogranin A, and S100 in pancreatic neuroendocrine neoplasms. Given the limited number of PanNET G3 and NEC cases and the absence of a comparison group, further studies with larger sample sizes and appropriate study designs are warranted to further investigate the significance of S100 expression in pancreatic neuroendocrine neoplasms.