Abstract

Background: Poorly differentiated gastric adenocarcinoma, particularly poorly cohesive carcinoma and signet-ring cell carcinoma (SRCC), represents a biologically heterogeneous group of tumors frequently associated with adverse histopathological features. Accurate identification of signet-ring cell components on routine hematoxylin-eosin (H&E) sections may be challenging in some cases. Periodic Acid–Schiff (PAS) and Alcian Blue (AB) staining can highlight intracellular mucin and may provide additional information for histopathological classification and tumor characterization. Objectives: To investigate PAS and Alcian Blue expression in poorly differentiated gastric adenocarcinoma, evaluate their role in histopathological reclassification, and assess their association with adverse histopathological features. Materials and Methods: A retrospective cross-sectional study was conducted on 144 cases of poorly differentiated gastric adenocarcinoma treated by partial or total gastrectomy at University Medical Center Ho Chi Minh City between January 2022 and January 2025. All cases were reviewed on H&E sections and subsequently stained with PAS and Alcian Blue (pH 2.5). Staining expression was assessed using a semi-quantitative immunoreactive score (IRS)-based system. Results: The mean age was 60.1 ± 11.8 years, with a male-to-female ratio of 1.8:1. Advanced-stage disease was observed in 68.1% of cases, lymph node metastasis in 79.9%, and perineural invasion in 75.0%. Histopathological classification changed after PAS and AB staining in 39 of 144 cases (27.1%). Notably, 47.2% of poorly cohesive carcinomas with signet-ring cell components were reclassified as signet-ring cell carcinoma after additional staining. Strong PAS expression was associated with early-stage disease and lower rates of perineural invasion, whereas strong AB expression was associated with lymph node metastasis and advanced-stage disease. An AB/PAS ratio > 0.5 was significantly associated with vascular invasion, perineural invasion, lymph node metastasis, and advanced-stage disease. Conclusions: PAS and Alcian Blue staining may facilitate the identification of signet-ring cell components and contribute to histopathological reclassification in a substantial proportion of poorly differentiated gastric adenocarcinomas. PAS expression, AB expression, and the AB/PAS ratio were significantly associated with adverse histopathological features.