Discordance rate of PD-L1 expression between primary and metastatic lesions in urothelial carcinoma (UC).

Abstract

493 Background: Immune checkpoint inhibitors (ICI) targeting PD-1 or PD-L1 are effective in select patients with advanced UC. High PD-L1 expression enriches for response to ICIs; however, the predictive value of PD-L1 expression is limited, which may be due in part to dynamic expression of PD-L1 in the tumor environment. We sought to characterize PD-L1 expression in primary UC and paired metastatic lesions to gain insight into the potential temporal discordance of tumor PD-L1 expression during the metastatic process. Methods: Immunohistochemical (IHC) staining for PD-L1 using the SP-142 antibody was performed on primary tumors and matched metastatic specimens in 83 patients with advanced UC. IHC staining was scored for the percentage of cells positive ( < 5%, ≥5%) in tumor cell (TC) and immune cell (IC) compartments. Correlation of PD-L1 expression in TCs and ICs was estimated using Spearman’s correlation coefficients (ρ). Cohen’s kappa statistics (κ) were utilized to assess the agreement in PD-L1 expression between groups. Results: High (≥5%) PD-L1 expression in primary and metastatic biopsies, respectively, was observed in 6.1% and 14.6% of TCs and in 7.8% and 11.7% of ICs. High co-expression of PD-L1 in both TC and IC compartments was infrequent in primary and metastatic lesions (3.6% and 2.6%, respectively). PD-L1 expression in TCs was positively correlated with PD-L1 expression in ICs in primary tumors (ρ = 0.47) and in metastatic lesions (ρ = 0.27). TC PD-L1 expression in primary tumors was correlated with TC PD-L1 expression in paired metastatic lesions (ρ = 0.44) but there was minimal agreement in high expression rates between primary and metastatic lesions in the TC compartment (κ = 0.147). IC PD-L1 expression in primary tumors was not correlated with IC PD-L1 expression in paired metastatic lesions (ρ = 0.05) and there was poor agreement in high expression rates between primary and metastatic lesions in the IC compartment (κ = 0.086). Conclusions: High PD-L1 IC expression is temporally discordant between primary and metastatic UC lesions. Future studies of PD-1/PD-L1 targeted therapies in patients with metastatic UC should utilize recent biopsies of metastatic lesions to define PD-L1 expression when feasible.