Tumour mutational burden (TMB) is a measurement of DNA variants in a tumour and is a potential biomarker of response to Immune Checkpoint Inhibitor (ICI) therapy. Patients with non-small cell lung cancer (NSCLC) whose tumours have a high TMB (≥10 mutations/Mb) might benefit from upfront ICI combination therapy. Clinical trials have measured TMB using Whole Exome Sequencing (WES) and/or the FoundationOne CDx (F1CDx) assay. In parallel, several commercial next-generation sequencing (NGS) assays have become available. Before implementation of TMB testing in clinical practice, technical and clinical validation are needed. Hence, a multi-center study was organised to establish concordance between several TMB assays.
Fifteen resection NSCLC formalin-fixed paraffin-embedded (FFPE) samples with broad TMB range were selected. Each participant received extracted DNA and was asked to report TMB values using their own protocol. In parallel, FFPE slides were analysed with F1CDx. Eight labs participated using five different methods: Oncomine TML assay (Thermofisher; n = 4), TSO500 assay (Illumina; n = 1), NEOplus assay (NEO New Oncology; n = 1), a 0,4 Mb targeted resequencing lab-developed assay (LDT; n = 1) and WES using three different TMB calculation methods (n = 1). Correlations between each platform and F1CDx were calculated. Also, the reported TMB category (high vs low) of the different platforms in comparison to F1CDx was evaluated for the fifteen samples.
Assessment of TMB values obtained by the platforms and F1CDx demonstrated a high correlation (R2 between 0.81 and 0.94), except for the smaller LDT (R2 = 0.53). The TMB category (high vs low) reported by each platform showed concordance with the F1CDx category for eleven (73%) to thirteen (93%) of the fifteen samples. From the fifteen samples, the same category was reported by all different platforms for seven (47%) samples.
Our data show that assays from different providers can be used to predict TMB. However, samples with a TMB value around the cut-off of 10 mut/Mb are challenging and interpretation should occur with caution. Further studies are required before implementing these assays in routine clinical diagnosis.
The authors.
Bristol-Myers Squibb.
S. Lambin: Research grant / Funding (institution): Bristol-Myers Squibb. All other authors have declared no conflicts of interest.