Precision or perplexity: Assessment of discordance among different PD-L1 assays in the same specimen in advanced non–small cell lung cancer in a community setting.

Abstract

e14579 Background: PD-L1 expression guides immunotherapy selection in NSCLC, yet multiple assays are used interchangeably despite known analytic variability. Real-world concordance across PD-L1 assays in community oncology practice is poorly characterized. Methods: We retrospectively analyzed PDL-1 expression data among 40 advanced NSCLC patients diagnosed in 2024 at a community oncology practice. PD-L1 testing was performed on each specimen using 22C3 (Pembrolizumab), 28-8 (Nivolumab), and SP142 assays (Atezolizumab). Positivity patterns (1% or higher) and inter-assay concordance were evaluated. Results: Among 40 Metastatic NSCLC patients, 40 underwent PD-L1 testing. 35 patients had all three assays performed on the same specimen (n = 35) PD-L1 positivity rates differed substantially: Complete concordance across all three assays occurred in only 11 PDL-1 positive patients (31%), while 10 (29%) were PDL-1 negative across all assays. Clinically significant discordance was frequent: 12 patients (34%) were positive by 22C3 and 28-8 but negative by SP142 Additional discordance included isolated positivity by 28-8 (n = 1) or SP142 (n = 1). In total PDL-1 assay discordance was seen in 14/35 patients (40%). Conclusions: Substantial inter-assay variability in PD-L1 expression in the same tissue specimen was observed in this community NSCLC cohort. However, due to concerns regarding costs and tissue exhaustion, additional and ongoing real-world data needs to be explored to determine the clinical utility of multiple versus a single umbrella PDL-1 assay in this setting.