PD-L1 testing in urothelial bladder cancer: essentials of clinical practice

International audience; Purpose: While immunotherapy has become an increasingly attractive strategy in patients with urothelial bladder cancer, the need for a biomarker to identify patients whose cancer is the most likely to respond has never been more crucial. This review systematically evaluates evidence regarding PD-L1 as a predictive biomarker of response to anti-PD(L)1 monoclonal antibodies in patients with urothelial bladder carcinoma, and discusses its current limits in routine clinical practice. Methods: We performed a critical review of PubMed/Medline according to the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA) statement. Prospective clinical trials evaluating anti-PD(L)1 monoclonal antibodies in urothelial bladder carcinoma together with retrospective studies evaluating PD-L1 expression in patients with bladder cancer were included. Results: Evidence data related to PD-L1 as a predictive biomarker of response to immune checkpoint blockade monotherapy across clinical trials are detailed in this review. The different companion diagnostic assays, and the methods for PD-L1 scoring in urothelial bladder carcinoma are reported. Additionally, the issues related to the implementation of PD-L1 testing in clinical practice are discussed. Conclusions: PD-(L)1 monoclonal antibodies atezolizumab and pembrolizumab are restricted to patients with PD-L1 positive status in the first-line setting in patients with advanced or metastatic urothelial bladder carcinoma who are ineligible to cisplatin-based chemotherapy. Importantly, the use of anti-PD(L)1 mAb in the other clinical settings is not based on PD-L1 status, but rather on patients’ clinical characteristics. Further identification of biomarkers with high negative predictive value will also be of utmost importance to identify patients who may not respond to such immunotherapies.