Tumor mutation burden derived from small next generation sequencing targeted gene panel as an initial screening method

Background: With the increasing use of immune checkpoint inhibitors, tumor mutation burden (TMB) assessment is now routinely included in reports generated from targeted sequencing with large gene panels; however, not all patients require comprehensive profiling with large panels. Our study aims to explore the feasibility of using a small 56-gene panel as a screening method for TMB prediction. Methods: TMB from 406 non-small cell lung cancer (NSCLC) patients was estimated using a large 520-gene panel simulated with the prospective TMB status for the small panel. This information was then used to determine the optimal cut-off. An independent cohort of 30 NSCLC patients was sequenced with both panels to confirm the cut-off value. Results: By comparing sensitivity, specificity, and positive predictive value (PPV), the cut-off was set up as 10 mutations/megabase, yielding 81.4% specificity, 83.6% sensitivity, and 62.4% PPV. Further validation with an independent cohort sequenced with both panels using the same cut-off achieved 95.7% sensitivity, 71.4% specificity and 91.7% PPV. The decreasing trend of sensitivity with the increasing trend of both specificity and PPV with a concomitant increase in the cut-off for the small panel suggests that TMB is overestimated but highly unlikely to yield false-positive results. Hence, patients with low TMB (<10) can be reliably stratified from patients with high TMB (>= 10). Conclusions: The small panel, more cost-effective, can be used as a screening method to screen for patients with low TMB, while patients with TMB >= 10 are recommended for further validation with a larger panel.