Microsatellite status and its correlation with clinicopathological features in gastric carcinoma: insights from a retrospective study in Northern Pretoria

Introduction/background: Gastric carcinomas (GC) are heterogeneous malignancies characterised by distinct histological and molecular subtypes. The microsatellite instability (MSI) molecular subtype, resulting from deficient DNA mismatch repair (dMMR), accounts for approximately 22% of global GC cases. Empirical evidence indicates differences in clinicopathological features, demographics, and treatment response in MSI GC compared to microsatellite stable (MSS) GC. MSI status has emerged as a potential biomarker for advanced GC, and this study aimed to determine the MSI prevalence of histopathologically confirmed GC cases at our centre. Method and material: This was a retrospective cross-sectional analysis of GC cases from 2018 to 2022, which were retrieved from the laboratory information system. DNA from these cases was isolated and assessed for MSI using a pentaplex PCR panel and confirmatory IHC on MSI-H was performed. Samples with no allelic size variation in the 5 microsatellite markers were classified as microsatellite stable (MSS), variation in 1 marker as microsatellite instability low (MSI-L), and variation in 2 or more microsatellite markers as MSI-H. Results: The study consisted of 64 cases with a MSI prevalence of 21.9% (n = 14) displaying a male predominance (n = 10; 71.4%) and a mean age of 62.7 years. Among these 14 MSI cases, 42.9% (n = 6) were classified as MSI-H with a mean age of 59.3 years. Half (n = 3) of these cases presented with upper gastrointestinal bleeding, with a majority of them diagnosed with moderately differentiated adenocarcinomas (66.7%). Microsatellite instability low was seen in 57.1% (n = 8) of the cases with a mean age of 65.3 years, and of these, patients presented with vomiting, epigastric pain and dysphagia with equal frequency at 25% (n = 2 respectively). Conclusion: The frequency of MSI cases in this study is congruent with global trends, highlighting the importance of microsatellite status in GC for understanding clinicopathological differences between MSI and MSS patients. These findings support the potential of MSI status as a biomarker.