We assessed the association between microsatellite instability-high (MSI-H) and tumor response to neoadjuvant chemotherapy (NAC) as well as its prognostic relevance in patients with clinical stage III gastric cancer (cStage III GC).
The NAC + surgery and the control cohorts consisted of 177 and 513 cStage III GC patients, respectively. The clinical and pathological features were compared between patients with MSI-H [n=57 (8.3%)] and microsatellite stability or microsatellite instability-low (MSS/MSI-L) [n=633 (91.7%)]. Radiological and histological response to NAC were evaluated based on response evaluation criteria in solid tumors (RECIST) and tumor regression grade (TRG) systems, respectively. The log-rank test and Cox analysis were used to determine the survival associated with MSI status as well as tumor regression between the two groups in both NAC + surgery and the control cohorts.
A statistically significant association was found between MSI-H and poor histological response to NAC (
MSI-H was associated with poorer regression and better survival after NAC for cStage III GC. TRG evaluation had prognostic significance in MSS/MSI-L but not in MSI-H. Further studies are needed to assess the value of NAC for cStage III GC patients with MSI-H phenotype.