Blood-Based Biomarkers for Cancer Immunotherapy: Tumor Mutational Burden in Blood (bTMB) is Associated with Improved Atezolizumab (atezo) Efficacy in 2L+ NSCLC (POPLAR and OAK)

Background:

Atezo (anti-PD-L1) was FDA approved for 2L+ NSCLC based on results from the randomized OAK and POPLAR trials, with atezo showing superior efficacy vs. docetaxel (doc). We previously showed that TMB in tissue correlates with atezo efficacy in 1L+ NSCLC. To address the significant challenge of consistently obtaining sufficient tumor tissue for molecular testing, we developed a novel blood-based assay to measure bTMB. Here we analyzed plasma samples from OAK and POPLAR with the bTMB assay to correlate bTMB with atezo clinical activity.

Methods:

The biomarker evaluable population (BEP) included 211 pts in POPLAR (ITT = 287) and 583 pts in OAK (excludes pts with known EGFR/ALK mutations; ITT = 850), with blood samples available for targeted genomic sequencing. The bTMB assay interrogates single nucleotide variants (SNVs) in 394 genes from cell-free DNA in plasma and reports a score based on the number of high-confidence SNVs identified. The BEP was grouped by bTMB cut points based on the minimum number of SNVs present.

Results:

In POPLAR, improved PFS and OS HRs with atezo vs. doc were observed at a range of bTMB cut points compared with the ITT and BEP. In OAK, PFS benefit with atezo vs. doc was observed at bTMB cut points ≥10 compared with BEP. (Table) Importantly, bTMB did not correlate with PD-L1 expression (SP142 or 22C3).

Conclusion:

These exploratory analyses represent the first demonstration of a novel blood-based assay measuring bTMB that may predict atezo clinical efficacy in 2L+ NSCLC. Thus, the bTMB assay may provide a non-invasive biomarker to identify pts who may derive clinical benefit from single agent checkpoint inhibition. Prospective studies using bTMB are currently ongoing in pts with 1L NSCLC (B-F1RST/BFAST).

NCT02008227; NCT01903993