Investigation Of Pd-L1 Expression And Response To Pembrolizumab (Pembro) In Gastric Cancer (Gc) And Cervical Cancer (Cc) Using Combined Positive Score (Cps) And Tumor Proportion Score (Tps).

4065Background: TPS, the percentage of viable tumor cells with partial or complete membrane staining at any intensity, has been invaluable for assessing PD-L1 expression in non–small cell lung cancer (NSCLC) and identifying patients (pts) likely to respond to anti-PD–1/PD-L1 therapy. However, TPS has limited utility beyond NSCLC. We investigated the predictive value of TPS and CPS and their association with response to pembro in pts with GC and CC. Methods: Tumor samples from pts with previously treated GC (KEYNOTE-059, NCT02335411) or CC (KEYNOTE-158, NCT02628067) were analyzed for PD-L1 expression per an investigational-use-only-labeled version of the PD-L1 IHC 22C3 pharmDx assay (Agilent Technologies). Response was assessed per RECIST v1.1 by independent review. External reproducibility of CPS, the number of PD-L1–staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100, was assessed. Results: Response, prevalence, positive predictive v...