Clinical Implications of Circulating Tumor DNA Tumor Mutational Burden (ctDNA TMB) in Non-Small Cell Lung Cancer.

BACKGROUND: Tissue tumor mutational burden (TMB) has emerged as a potential biomarker predicting response to anti-programmed cell death-1 protein receptor (PD-1)/programmed cell death-1 protein ligand (PD-L1) therapy, but few studies have explored using circulating tumor DNA (ctDNA) TMB in non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: A total of 136 patients with NSCLC with ctDNA testing were retrospectively evaluated from a single institution, along with a validation cohort from a second institution. ctDNA TMB was derived using the number of detected mutations over the DNA sequencing length. RESULTS: Higher ctDNA TMB was significantly correlated with smoking history (p < .05, chi-squared test). Among patients treated with immune checkpoint inhibitors (n = 20), higher ctDNA TMB was significantly correlated with shorter progressive free survival (PFS) and overall survival (OS; 45 vs. 355 days; hazard ratio [HR], 5.6; 95% confidence interval [CI], 1.3-24.6; p < .01, and OS 106 days vs. not reached; HR, 6.0; 95% CI, 1.3-27.1; p < .01, respectively). In a small independent validation cohort (n = 12), there was a nonsignificant numerical difference for higher ctDNA TMB predicting shorter OS but not PFS. ctDNA TMB was not correlated with RECIST tumor burden estimation in the subset of patients treated with immune checkpoint blockade. CONCLUSION: The findings indicate that higher ctDNA TMB, at the current commercial sequencing length, reflects worse clinical outcomes. IMPLICATIONS FOR PRACTICE: Biomarkers to identify patients who will respond to immune checkpoint blockade are critical. Tissue tumor mutational burden (TMB) has emerged as a viable biomarker to predict response to anti-PD-1/PD-L1 therapy, but few studies have explored the meaning and potential clinical significance of noninvasive, blood-based TMB. Here, we investigated circulating tumor DNA (ctDNA) TMB and present data demonstrating that current ctDNA TMB may reflect tumor burden and that ctDNA panels with a greater number of mutations may be necessary to more accurately reflect tissue TMB.

Large-Cell Neuroendocrine Carcinoma of the Lung: A Focused Analysis of BRAF Alterations and Case Report of a BRAF Non-V600-Mutated Tumor Responding to Targeted Therapy.

PURPOSE: In advanced stages, large-cell neuroendocrine carcinoma of the lung (L-LCNEC) mimics small-cell lung cancer despite its traditional classification as a non-small-cell lung cancer. Here we present a focused analysis of BRAF mutations in this population. PATIENTS AND METHODS: Comprehensive genomic profiling of tumor tissues was performed from a cohort of 300 patients with biopsy-proven L-LCNEC. Specimens were either from a primary lung lesion or metastatic site. RESULTS: In 13 patients, 14 unique BRAF alterations (amplifications, mutations) were identified. The importance of biomarker-driven therapy is subsequently highlighted with our case of a 69-year-old man diagnosed with metastatic L-LCNEC who did not respond to cisplatin plus etoposide. A significant durable response was then demonstrated with therapy targeted toward a BRAF non-V600E activating mutation (G469R) associated with biomarker response identified through circulating cell-free tumor DNA analysis. A change in clonal allele frequency from nearly 40% to nondetectable was observed. CONCLUSION: Although uncommon, L-LCNEC does seem to contain activating and therefore actionable alterations. We thus highlight the value of pursuing next-generation sequencing for patients with this disease.