Blood tumor mutational burden (bTMB) represents the total number of mutations per coding area of a tumor genome calculated through the genomic sequencing of circulating tumor DNA (ctDNA), an alternative source of diagnostic material for patients with inadequate tissue samples. The value of bTMB has been found to correlate with the efficacy of anti-PD-L1/PD-1 immunotherapies in some tumor types.
NovoPM™ 2.0-bTMB Algorithm
- bTMB is calculated based on the coding DNA sequence (CDS) regions included in the NovoPM™ 2.0 panel (approximately 1.4 Mb).
- Somatic mutations are identified by VarScan2.
- The following mutations are excluded from the calculation of bTMB:
- Germline mutations
- Low frequency mutations (Threshold: SNV 0.8%; InDel 1.5%)
- Known driver mutations (EGFR, MET, BRAF, PIK3CA, NF1, KRAS, and NOTCH family)
- Synonymous mutations
- Repeat regions
NovoPM™ 2.0-bTMB Algorithm Validation
To analytically validate our NovoPM™ 2.0-bTMB algorithm, we sequenced 48 paired FFPE tumor tissue samples and ctDNA samples with NovoPM™ 2.0. TMB and bTMB were then calculated according to the algorithms. The results showed good linear correlation (Figure 1A; R2=0.7039). The reproducibility was validated by 8 samples with triplicate and the result is shown in Figure 1B.
Figure 1. Performance validation of NovoPM™ 2.0-bTMB. A. Concordance of NovoPM™ 2.0-bTMB and TMB from 48 paired tissue-blood samples. X-axis: bTMB result from NovoPM™ 2.0-bTMB; Y-axis: TMB result from NovoPM™ 2.0-TMB; B. Reproducibility of NovoPMTM 2.0-bTMB (12.5% of average CV from 8 samples with triplicate).