The PD-1, PD-L1 expression and CD3+ T cell infiltration in relation to outcome in advanced gastric signet-ring cell carcinoma, representing a potential biomarker for immunotherapy

Recent data supports a potentially significant role for immune checkpoint inhibitors in the treatment of gastric cancer. However, there are few data on the clinical implications of immunotherapy markers in gastric signet-ring cell carcinoma (SRCC). We evaluated the expression of programmed cell death protein-1 (PD-1), programmed cell death ligand 1(PD-L1), infiltration by CD3+ T cell, microsatellite instability (MSI), and Epstein-Barr Virus (EBV), and the relationship of each factor to survival in 89 advanced SRCC patients. All patients received 5-FU-based first-line chemotherapy. PD-L1 and PD-1 were expressed in 40.4% and 18.0% of the patients, respectively. There was a significant correlation between PD-L1 and PD-1 expression (r=0.363, p<0.001). There was loss of at least 1 of the 4 DNA mismatch repair (DNA-MMR) gene proteins in 32.6% of samples. Only 1 case out of 89 was EBV positive, with concurrent PD-L1 positivity, a high degree of CD3+ T cell infiltration and MSI. Increased CD3+ T cells numbers was associated with increased PD-1 expression (r=0.256, p=0.012) and MSI status (r=0.208, p=0.049). High CD3+ T cell infiltration was related to better OS (23.7 months, 95% CI: 19.0-38.0 vs 15.8 months, 95% CI: 13.0-22.0, p=0.033), but was not an independent prognostic factor for survival after multivariate analysis (HR=0.68, 95% CI: 0.42-1.10, p=0.116). CD3+ T cell was more infiltrated in PD-1 positive, tumors with MSI and were associated with better OS, indicating an adaptive immune resistance may be occurring. Further research into the cancer immunotherapy markers of SRCC immune microenvironment may highlight targets for immunotherapy.