Development of a quantitative PD-L1 assay using laser capture microdissection (LCM)-based reverse phase protein microarray (RPPA) workflow: Implications for precision medicine.

35Background: FDA approved IHC-based companion/complementary assays are routinely used to measure PD-L1 for treatment selection. However, IHC cut-point values vary across platforms and are based on subjective analysis that requires antigen retrieval methods. Even in highly selected populations of PD-L1 “positive” patients, clinical benefits are seen only in subgroups of patients. We tested the feasibility of utilizing LCM and RPPA as a new methodology for quantitative, operator independent measurements of PD-L1 on tumor cells. Methods: PD-L1 quantification by RPPA was compared to IHC on 23 lung cancers (LC). Tumor cells were isolated from the surrounding microenvironment using LCM. The E1L3N clone from Cell Signaling was used to quantify PD-L1 expression by RPPA and IHC. Reproducibility across antibody clones was then assessed on LCM procured tumor epithelia from 10 FFPE LC and 71 snap-frozen ovarian cancers (OC). PD-L1 measurements were compared between the Cell Signaling E1L3N and the Ventana SP-142 clo...