ABSTRACT
Objective: To investigate the expressions of CD8, CD68, PD-1 and PD-L1 in microsatellite stability/instability (MSS/MSI) gastric cancer and the prognostic value of microsatellite stability. Methods: Sixty consecutive primary gastric cancer samples were collected from March 2012 to August 2012. The clinical pathological and survival information was collected as well. Immunohistochemistry of MLH1, MSH2, MSH6, PMS2, CD8, CD68, PD-1 and PD-L1 was conducted for each sample. The survival prognosis was analyzed by log-rank test. Results: There were 15 MSI gastric cancer samples (25.0%) with negative staining of MLH1, MSH2, MSH6 and PMS2. There was no significant difference in the expression of CD8, PD-1 or PD-L1 between MSS and MSI gastric cancer, but the CD68 positive macrophages infiltration was higher in MSS than in MSI gastric cancer (P=0.046). Type Ⅱ (CD8-PD-L1-) was the major immune type (46.67%) in MSI gastric cancer, and the main immune type of MSS gastric cancer was type Ⅱ (33.33%) and type (CD8+PD-L1-, 31.11%). The disease-free survival (P=0.036) and overall survival (P=0.041) in MSI gastric cancer was longer than in MSS. Conclusion: MSI gastric cancer predicts a better prognosis although the tumor microenvironment shows a lower immune response.