Abstract

Background: The DNA mismatch repair (MMR) system plays a critical role in maintaining genomic stability and is associated with response to immunotherapy in cancer. In prostate adenocarcinoma, MMR deficiency is relatively uncommon but clinically relevant. However, the performance of immunohistochemistry (IHC) is highly dependent on technical protocols, necessitating optimization. Objective: To optimize the immunohistochemical staining protocol for MMR proteins, including MSH2, MSH6, MLH1, and PMS2, and to evaluate the feasibility of its application in prostate adenocarcinoma. Materials and Methods: A cross-sectional descriptive study was conducted on 138 cases of histologically confirmed prostate adenocarcinoma at the Department of Pathology, Binh Dan Hospital. Tissue microarray (TMA) was constructed with three cores per case. IHC staining was performed using the automated BenchMark XT system. Protocol optimization was achieved by adjusting antigen retrieval time, primary antibody incubation time, detection system duration, and signal amplification. Results: MMR protein expression was retained in 131/138 cases (94.9%), while 7/138 cases (5.1%) showed loss of expression. MSH6 required longer antigen retrieval, PMS2 required extended antibody incubation, and both MLH1 and PMS2 required signal amplification. The optimized protocol yielded clear nuclear staining, low background staining, and well-preserved internal controls. Conclusion: The optimized IHC protocol demonstrated high reliability and is suitable for implementation in routine diagnostic practice.