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TMB measured by NGS may ID SCLC patients who will benefit from immunotherapy



High tumor mutational burden and development of immune-related adverse events are markers of response to immune checkpoint inhibitor therapy in patients with small cell lung cancer, and targeted next-generation sequencing may help identify those likely to benefit from immunotherapy, findings from a case series suggest.

Of 113 small cell lung cancer (SCLC) patients who had successful next-generation sequencing (NGS) with tumor mutational burden (TMB) assessment at the Dana-Farber Cancer Institute (DFCI) in Boston, 52 were treated with immune checkpoint inhibitors and 61 received chemotherapy but never received subsequent immunotherapy, Biagio Ricciuti, MD, of DFCI said at the annual meeting of the Society for the Immunotherapy of Cancer.

Median TMB for all patients was 9.68 mutations/megabase, with those with TMB above the median considered TMB high, and those with TMB below the median considered TMB low. Median progression-free survival (PFS) was significantly longer among TMB-high versus TMB-low patients (3.3 vs. 1.2 months; hazard ratio, 0.37), as was median overall survival (OS, 10.4 vs. 2.5 months; HR, 0.38), he said.

“To confirm that TMB was a predictive biomarker for immunotherapy only, we also looked at the outcome with chemotherapy according to tumor mutational burden, and as expected we found no difference in terms of median progression-free survival or median overall survival according to TMB-high versus TMB-low groups,” he said.

Additionally, patients with SCLC who were treated with immune checkpoint inhibitors and experienced at least one immune-related adverse event had significantly better median PFS and OS than did patients who experienced no immune-related adverse events (6.7 vs. 1.3 months; HR, 0.25; and 17.9 vs. 2.9 months; HR, 0.27, respectively), he said, noting that, in a 12-week landmark analysis, the differences in PFS and OS between the groups were “nearly double” but did not reach statistical significance.

TMB in the SCLC patients in this study was assessed using the DFCI NGS OncoPanel platform of more than 450 genes, and the TMB-high and TMB-low groups were similar with respect to baseline clinical and pathological features and known prognostic factors, Dr. Ricciuti said.

Prior studies have demonstrated that high TMB as assessed by whole exome sequencing correlates with benefits from immunotherapy. However, “whole exome sequencing is a very expensive technique, it’s challenging ... and it’s not really available to oncologists across countries,” he said.

Whether the more readily available targeted NGS could help identify the small fraction of SCLC patients who are likely to benefit from immunotherapy has been unclear, as has the relationship between the development of irAEs and immunotherapy response in SCLC; factors associated with clinical benefit from immunotherapy have not previously been well characterized, Dr. Ricciuti noted.

The current findings, though limited by the retrospective study design and small sample size, provide the first evidence for the use of targeted NGS panels to identify patients with advanced SCLC who are most likely to benefit from immunotherapy, he said, adding that, when compared with whole genome sequencing, TMB as assessed using targeted NGS “may offer a very useful tool for clinicians to optimize small cell lung cancer patient selection for immunotherapy.

“Our study also suggests that immune-related adverse events might be associated with improved efficacy of immunotherapy, although larger studies with longer follow-up are required to confirm this finding,” he concluded.

Dr. Ricciuti reported having no disclosures.

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