1281O Atezolizumab (atezo) vs platinum-based chemo in blood-based tumour mutational burden-positive (bTMB+) patients (pts) with first-line (1L) advanced/metastatic (m)NSCLC: Results of the Blood First Assay Screening Trial (BFAST) phase III cohort C

Abstract

Background: TMB is a promising biomarker for immunotherapy in NSCLC, but current data are mostly retrospective. As not all pts may have sufficient tissue for comprehensive biomarker testing, bTMB was prospectively tested as a novel biomarker using targeted next-generation sequencing. BFAST (NCT03178552), a global, open-label, multi-cohort trial, evaluated safety and efficacy of targeted therapies or immunotherapy in biomarker-selected pts with unresectable mNSCLC. Here we present results from Cohort C of 1L atezo vs platinum-based chemo in pts with bTMB+ mNSCLC. Methods: We planned to randomise ≈440 pts with 1L mNSCLC with measurable disease per RECIST 1.1 and bTMB ≥10 (9.1 mut/Mb; FMI bTMB assay) 1:1 to atezo 1200 mg IV every 3 weeks or chemo and stratified by tissue availability, ECOG PS, bTMB and histology. The primary endpoint was INV-PFS per RECIST 1.1 in bTMB ≥16 (14.5 mut/Mb) pts. Key secondary endpoints included OS in bTMB ≥10 (intent to treat, ITT) and bTMB ≥16 pts, and INV-PFS in ITT pts. Results: 471 pts were assigned to atezo (n=234) or chemo (n=237). At baseline, 72% had non-squamous histology, 2% never smoked and median SLD was 103 mm. 145 pts with bTMB ≥16 were assigned to atezo and 146 to chemo. At data cutoff (21 May 2020) minimum follow up was 6 mo. INV-PFS difference in bTMB ≥16 pts for atezo vs chemo was not significant (P=0.053; Table). Grade 3-4 TRAEs occurred in 18% (atezo) vs 46% (chemo) of pts. Serious TRAEs occurred in 12% (atezo) vs 14% (chemo). Results at other bTMB thresholds and by F1L CDx will also be presented as an exploratory analysis. Conclusions: The primary PFS endpoint in bTMB ≥16 pts was not met. OS was numerically better with atezo vs chemo but the difference was not statistically significant. The safety profile of atezo vs chemo was favourable and consistent with atezo monotherapy across indications