Prognostic role of mismatch repair status in stage II colon cancer at Ho Chi Minh City Oncology Hospital.

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Background: Colon cancer is among the leading causes of cancer incidence and mortality in Vietnam according to GLOBOCAN 2022. In stage II colon cancer, mismatch repair (MMR) status determined by immunohistochemistry is an important biomarker for prognostic assessment and selection of patients who may benefit from adjuvant chemotherapy. Methods: A retrospective descriptive study was conducted in 185 patients with stage II colon cancer treated at Ho Chi Minh City Oncology Hospital between January 1, 2017 and December 31, 2020. MMR status was evaluated by immunohistochemistry. Five-year disease-free survival (DFS) and overall survival (OS) were analyzed according to MMR status. Multivariate Cox regression was performed to identify prognostic factors. Results: Deficient MMR (dMMR) was identified in 33% of patients and proficient MMR (pMMR) in 67%. Among dMMR tumors, concurrent loss of MLH1/PMS2 and MSH2/MSH6 expression were the most frequent patterns (42.6% and 31.2%, respectively). The 5-year DFS rate was 97.8% in the dMMR group and 82.2% in the pMMR group (p=0.005). The 5-year OS rate was 97.9% and 87.2%, respectively (p=0.132). The liver was the most common metastatic site in the pMMR group. On multivariate analysis, dMMR status was associated with DFS (HR=0.109, p=0.033), while bowel obstruction was associated with OS (HR=3.652, p=0.028). Conclusions: MMR status is an independent prognostic factor in stage II colon cancer. Patients with dMMR tumors demonstrate superior disease-free survival compared with those with pMMR, supporting the clinical relevance of routine MMR assessment in this population.