Discordance of high PD-L1 expression in primary and metastatic urothelial carcinoma lesions

Immune checkpoint inhibitors (ICI) targeting PD-(L)1 are effective in select patients with advanced urothelial carcinoma (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 discordance of tumor PD-L1 expression during the metastatic process.

Materials and methods: Immunohistochemical staining for PD-L1 using the SP-142 antibody was performed on primary tumors and matched metastatic specimens in 77 evaluable subjects with advanced UC. Immunohistochemical 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 (rho, 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 6.0% and 7.7% of TCs and in 14.5% and 11.5% of ICs. IC PD-L1 expression in primary tumors was not correlated with IC PD-L1 expression in paired metastatic lesions (ρ = 0.05, P = 0.67) and there was poor agreement in high expression rates between primary and metastatic lesions in the IC compartment (κ= 0.086).

Conclusion: High PD-L1 IC expression is temporally and spatially discordant between primary and metastatic UC lesions. Future studies of PD-(L)1 targeted therapies in patients with metastatic UC may benefit from use of fresh biopsies of metastatic lesions to define PD-L1 expression when feasible.