Different PD-L1 Assays Reveal Distinct Immunobiology and Clinical Outcomes in Urothelial Cancer

Galsky MD et al. Cancer Immunology Research

Different PD-L1 assays reveal distinct immunobiology and clinical outcomes in urothelial cancer

Programmed death-ligand 1 (PD-L1) has emerged as a pivotal biomarker in immuno-oncology (IO) trials, particularly for guiding therapeutic decisions. Leveraging its extensive experience, CellCarta has participated in over 200 trials, with its pathologists renowned for their proficiency in PD-L1 scoring across four distinct companion diagnostics (CDx) immunohistochemical (IHC) PD-L1 assays.

PD-L1 expression is observed on both tumor cells and immune cells; however, its differential significance across these cell types remains elusive in several solid tumors. Previous research conducted by CellCarta revealed assay-dependent variability in PD-L1 staining patterns, with notable distinctions between tumor and immune cell expression. Interestingly, the PD-L1 clone SP142 assay showed more intense staining for immune cells compared to other PD-L1 assays.

A recent study published in Cancer Immunology Research demonstrated that bladder cancer patients who predominantly displayed PD-L1 expression on immune cells showed an improved response to checkpoint inhibitors compared to those where PD-L1 expression was confined to tumor cells.

CellCarta scientists Mark Kockx and Roos Van Elzen co-authored this paper and were closely involved in the analysis of various PD-L1 assays used in this bladder cancer IO study. Furthermore, the research elucidated the unique staining characteristics of one assay through advanced techniques such as multiplex IHC and immunofluorescence (IF).

Additionally, the CellCarta team validated a double-staining assay to measure PD-L1 on both tumor cells and dendritic cells, highlighting the necessity of PD-L1-based multiplex assays for optimizing patient selection in checkpoint inhibition therapies.