LAUSR

e14290 Background: Randomized trials have demonstrated that PD-L1 expression in tumor cells predicts for response to PD-1 or PD-L1 checkpoint inhibitors in advanced cancers. However, the frequency of discordance in PD-L1 expression between primary tumors and paired distant metastases is currently unclear. We aimed to determine the discordance rate of PD-L1 expression between primary tumor and paired distant metastases in advanced cancers. Methods: We searched MEDLINE and EMBASE for eligible studies. We noted the discordance rate (positive-to-negative or vice versa) and performed subgroup analyses based on the PD-L1 expression in primary tumor, locations of primary tumor and distant metastases, positivity thresholds and type of antibody used for testing. We used QUADAS-2 tool to assess the methodologic quality of the included studies. We performed the meta-analysis using the logistic-normal random effects model. Results: We identified 11 eligible studies including 351 cases of lung, colorectal, breast and ovarian cancers. Nine studies were judged to have low risk of bias in their methodological quality. The overall discordance rate in PD-L1 expression between primary tumor and paired distant metastases was 28% (95% confidence interval (CI) = 18-41) with significant heterogeneity among the studies (chi-square test P-value < 0.0001). There was no statistically significant differences in discordance rates between the subgroups: PD-L1-positive (40%, 95% CI = 21-63) vs PD-L1-negative primary tumors (21%, 95% CI = 12-34), lung primary (31%, 95% CI = 14-55) vs colorectal/ breast/ ovarian primary (27%, 95% CI = 19-37), central nervous system metastases (22%, 95% CI = 8-47) vs liver/ lung/ pleural/ peritoneum metastases (34%, 95% CI = 24-46); 1% (23%, 95% CI 16-33) vs 5% positivity threshold (33%, 95% CI 11-68); E1L3N (42%, 95% CI 10-82) vs SP142 antibody (27%, 95% CI 20-36). Conclusions: The discordance in PD-L1 expression between primary tumors and paired distant metastases is close to 30%, which could potentially affect response to immunotherapy. Further works exploring the mechanisms and impact of this discordance are warranted.