SY12-4 PD-L1 testing in gastric cancer

PD-L1 expression is an established predictive marker of response to immune checkpoint inhibitors for various types of cancer patients. At present, PD-L1 immunohistochemistry by 28-8 pharmDx is tested and evaluated using combined positive score (CPS) for HER2-negative advanced gastric cancer patients before initiating first-line treatment. However, PD-L1 testing is still a suboptimal method because of its interobserver variability due to the heterogeneous and complex staining patterns on both tumor cells and immune cells. This talk reviews the staining patterns of PD-L1 in each subtype of gastric cancer and the potential pitfalls that can be encountered in routine practice. In addition, predictive capability of PD-L1 CPS is limited in isolation, because other immune evasion strategies are also important in gastric cancer progression. Therefore, I’d like to discuss other predictive biomarkers for immune checkpoint inhibitors, with focus on mismatch repair deficiency/microsatellite instability, Epstein-Barr virus, and altered antigen presentation by HLA-class I.