Background: Mismatch repair deficient (dMMR) or microsatellite instability-high (MSI-H) serves as a predictor poor response to adjuvant chemotherapy in stage II colon cancer patients. Our objective was to investigate the efficacy of adjuvant chemotherapy in dMMR/MSI-H gastric cancer (GC).
Methods: We searched literatures through December, 2020 to identify clinical studies that reported survival comparing adjuvant chemotherapy with surgery alone in dMMR/MSI-H GCs. Two approaches were used to pool the hazard ratio (HR) of survival: (1) If Kaplan-Meier curves and number at risk were provided, individual patient data were extracted. Cox models were used to calculate the HR with 95% confidence interval (CI); (2) for study-level data, pooled HR was estimated using fixed/random-effects models.
Results: Six clinical studies were identified. For dMMR/MSI-H versus mismatch repair proficient (pMMR)/microsatellite stable (MSS)/microsatellite instability-low (MSI-L), the estimated 5-years DFS were 74.2% versus 51.5% (HR, 0.44; 95% CI, 0.32-0.62; P < 0.001); the estimated 5-years OS were 60.8% versus 50.1% (HR, 0.72; 95% CI, 0.60-0.88; P = 0.001). At study-level data, the pooled HRs were 0.42 for DFS (95% CI, 0.31-0.57; P < 0.001) and 0.66 for OS (95% CI, 0.32-1.38; P = 0.268). For adjuvant chemotherapy versus observation in dMMR/MSI-H, the estimated 5-years DFS were 76.1% versus 73.3% (HR, 0.72; 95% CI, 0.45-1.15; P = 0.171); the estimated 5-years OS were 74.9% versus 60.2% (HR, 0.60; 95% CI, 0.44-0.83; P = 0.001). Significant survival differences were also observed at study-level.
Conclusions: This study further suggested adjuvant chemotherapy could be beneficial even in dMMR/MSI-H GC patients.