The effect of chemotherapy on programmed death ligand-1 (PD-L1) and PD-L2 expression is not well known. Therefore we aimed to investigate the effect of chemotherapy to PD-L1/2 expression in metastatic gastric cancer (mGC).
We evaluated the PD-L1 and 2 expression of 63 patients with paired tumor tissue before and after 3 to 4 cycles of palliative first line platinum-based chemotherapy. PD-L1/2 expression was detected by immunohistochemistry(IHC) method in paired tumor specimens.
There were no significant differences in PD-L1 and PD-L2 expression across various clinicopathological parameters. The detection of PD-L1 on tumor cells decreased from 58% to 38% after chemotherapy (p = 0.028), but not with PD-L2 (from 43% to 36%). Among patients with objective response (CR and PR), PD-L1 expression decreased with statistical significance (p = 0.033), but not among patients with SD and PD (p = 0.275). In univariate and multivariate analysis, patients with positive PD-L1 at the pre-chemotherapy showed better progression free survival (PFS, hazard ratio [HR]=0.42, p = 0.014). In contrary, after chemotherapy, patients with positive PD-L1 showed decreased PFS (HR = 1.97, p = 0.023). And pre-chemotherapy PD-L1 statuses didn’t have any correlation with OS difference, however, post-chemotherapy negative PD-L1 prolonged OS (HR = 1.92, p = 0.047). PD-L2 statuses had no difference of PFS and OS before and after chemotherapy. Univariate and Multivariate analysis showed that negative to positive change and positive to negative change of PD-L1 expression was associated with poorer PFS (HR = 0.030, p = 0.03) and better PFS (HR = 0.02, p = 0.024), respectively.
Our data suggests that chemotherapy may have an effect on the status of PD-L1/L2 expression. PD-L1/L2 expression may change during chemotherapy, so we suggest monitoring the pattern of change through serial tumor samples to reflect the correct status of PD-L1 expression.
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All authors have declared no conflicts of interest.