Lynch Syndrome in Vietnamese Patients with Colorectal Cancer: Prevalence and Clinicopathologic Characteristics from a Single-Center Study

Background: Lynch syndrome (LS) is the most common hereditary cause of colorectal cancer (CRC), but the prevalence and clinical characteristics of this disorder among Vietnamese patients remain underreported. This study estimated the prevalence and described the clinical characteristics of LS in a hospital-based population in Vietnam. Methods: A cross-sectional study on prospective data was conducted at the University Medical Center, Ho Chi Minh City (2022–2024), including 190 CRC participants underwent panel genetic testing for LS-associated genes (MLH1, MSH2, MSH6, PMS2, EPCAM). Results: LS was diagnosed in 12/190 patients (6.3%); the prevalence for MLH1, MSH2, MSH6 mutations was 3.7%. The most frequent mutations were in MSH2 (25%) and PMS2 (33.3%). LS patients were significantly younger (49.7 ± 14.5 vs. 60.3 ± 12.1 years, p = 0.004), with 50% diagnosed before 50-year-old. Right-sided tumours were more common (58.3%). Most LS cases were in stage 3 (50%), and 58.3% had no family history of CRC. Conclusion: The LS prevalence in Vietnamese CRC patients was higher than expected, particularly for PMS2 mutations. 58.3% of LS patients had no family history, and 50% were aged ≥50 years, suggesting potential false negatives according to traditional screening criteria. Expanding genetic testing to older patients and those without a family history could improve LS detection and management.