Prevalence of Microsatellite Instability in Gastric and Gastroesophageal Junction Cancer patients from a Latin American Country

BACKGROUND: In Colombia, gastric cancer is fifth in incidence (12.8 cases per 100,000) and third in mortality (9.9 cases per 100,000). Microsatellite instability (MSI), a phenotype in gastric cancer treatment, lacks comprehensive exploration in Colombian and Hispanic/Latino populations. Data scarcity hinders immunotherapy approval in middle-income countries. OBJECTIVE: Characterize the prevalence of MSI phenotype in Colombian patients with gastric and gastroesophageal junction cancer. MATERIALS AND METHODS: We measured MLH-1, MSH-2, MSH-6, and PMS-2 expression in tumor pathology by immunohistochemistry markers. We conducted descriptive analysis and Fisher's test to identify associations for MSI expression. RESULTS: Final sample size was 106 patients, mean age of 62.5 years (25-93 ± 14.2). Prevalence of MSI was 12.26% (n = 13). We found an association between older age and positive MSI (p = 0.0042), as well as with non-diffuse histologic subtypes (p = 0.019). CONCLUSION: Prior studies report 22% MSI phenotype prevalence in gastric tumors, mostly in developed countries, excluding Hispanic/Latino populations. Identifying the prevalence of MSI in our population as 12.26% could pave the way for approving immune blockade drugs as a treatment option for these patients in Latin American countries. Our data could be utilized to conduct cost-utility studies in support of this.