LBA83 - Final efficacy results from B-F1RST, a prospective phase II trial evaluating blood-based tumour mutational burden (bTMB) as a predictive biomarker for atezolizumab (atezo) in 1L non-small cell lung cancer (NSCLC)

bTMB assays determine TMB using a noninvasive blood test. B-F1RST (ITT, n=152) is the first prospective trial to evaluate bTMB as a biomarker to predict benefit of 1L atezo monotherapy in advanced NSCLC. bTMB high (score of≥16; ≥ 14.5 mut/Mb) predicted better ORR with atezo vs bTMB low (< 16; 28.6% vs 4.4%) in the biomarker evaluable population (BEP) with ≥ 6mo follow up in the primary analysis. Numerical benefit for bTMB high was seen in median (m)PFS and mOS. Here we report the B-F1RST final analysis. Eligibility criteria included untreated stage IIIB-IVB NSCLC and ECOG PS 0/1. Pts received atezo 1200mg IV q3w until PD, intolerance or loss of benefit. Co-primary endpoints were investigator assessed ORR for efficacy (ITT) and PFS for biomarker analysis (BEP) at a prespecified bTMB cutoff of 16 for high (≥ 16) vs low (< 16). PFS and OS, a secondary endpoint, were further evaluated at various bTMB cutoffs. Serum C-reactive protein (CRP), an inflammation marker in cancer, was evaluated as a surrogate biomarker, ratio of CRP at C3D1 to CRP at screening, to predict PFS and OS. With ≥ 18mo follow up (data cutoff, 14 May 2019) in ITT pts, ORR was 17% (95% CI: 12, 24), mPFS was 4.1mo (95% CI: 2.8, 4.9) and mOS was 14.8mo (95% CI: 12.7, 21.3). In bTMB ≥ 16 vs