A blood-based immune marker for resistance to pembrolizumab in patients with metastatic urothelial cancer.

PD1 inhibition is effective in patients with metastatic urothelial cancer (mUC), yet a large fraction of patients does not respond. In this study, we aimed to identify a blood-based immune marker associated with non-response to facilitate patient selection for anti-PD1. To this end, we quantified 18 immune cell populations using multiplex flow cytometry in blood samples from 71 patients with mUC (as part of a biomarker discovery trial; NCT03263039, registration date 28-08-2017). Patients were classified as responder (ongoing complete or partial response, or stable disease; n = 25) or non-responder (progressive disease; n = 46) according to RECIST v1.1 at 6 months of treatment with pembrolizumab. We observed no differences in numbers of lymphocytes, T-cells, granulocytes, monocytes or their subsets between responders and non-responders at baseline. In contrast, analysis of ratios of immune cell populations revealed that a high mature neutrophil-to-T-cell ratio (MNTR) exclusively identified non-responders. In addition, the survival of patients with high versus low MNTR was poor: median overall survival (OS) 2.2 vs 8.9 months (hazard ratio (HR) 6.6; p < 0.00001), and median progression-free survival (PFS) 1.5 vs 5.2 months (HR 5.6; p < 0.0001). The associations with therapy response, OS, and PFS for the MNTR were stronger than for the classical neutrophil-to-lymphocyte ratio (HR for OS 3.5, and PFS 3) and the PD-L1 combined positivity score (HR for OS 1.9, and PFS 2.1). In conclusion, the MNTR distinctly and uniquely identified non-responders to treatment and may represent a novel pre-treatment blood-based immune metric to select patients with mUC for treatment with pembrolizumab.