Prevalence of programmed death ligand-1 (PD-L1) by demographic, disease and sample characteristics in unresectable, stage III NSCLC (PACIFIC)

Abstract

Background: PACIFIC (NCT02125461) was a randomised, placebo‐controlled, phase 3 trial evaluating the immune checkpoint inhibitor durvalumab in patients (pts) with unresectable, Stage III non‐small cell lung cancer (NSCLC) who did not have disease progression after concurrent chemoradiotherapy (cCRT). Both primary endpoints of progression‐free survival and overall survival were met and significantly improved with durvalumab, with similar safety, versus placebo (Antonia et al, NEJM 2017; 2018). We report exploratory analyses of the prevalence of tumour PD‐L1 expression by baseline pt, disease and sample characteristics and by response to prior treatment for pts in PACIFIC. Methods: If available (provision of formalin‐fixed paraffin‐embedded tumour resection or biopsy samples was optional), archived pre‐cCRT tumour tissue was tested retrospectively for PD‐L1 tumour cell (TC) expression using the VENTANA PD‐L1 (SP263) immunohistochemistry assay and scored at validated pre‐specified (≥25%) and post‐hoc (≥1%) cutoffs. Overall PD‐L1 prevalence (regardless of treatment arm) was summarised by pt subgroups defined by various characteristics, and assessed using a Pearson's chi‐squared test for between‐group differences. Results: Of 713 randomized pts, 451 (63.2%) were evaluable for PD‐L1 status. Among PD‐L1‐evaluable pts, 67.2% (303/451) had TC≥1% and 35.3% (159/451) had TC≥25% (similar to previous reports in metastatic NSCLC). PD‐L1 prevalence by various characteristics at the TC≥1% cut‐off are reported in the table. Conclusions: There were no important differences noted in PD‐L1 prevalence between relevant subgroups at the TC≥1% or TC≥25% cut‐offs (latter data to be presented). PD‐L1 status was unaffected by sample type or age or biopsy location, suggesting expression is stable from pre‐cCRT diagnostic biopsies, and supports the use of either primary tumour or lymph node biopsies for PD‐L1 testing. (Table Presented).