Background: Limited disease (LD) small cell lung cancer (SCLC) treated with definitive concurrent chemoradiotherapy (CCRT) potentially experience disease recurrence. We investigated the feasibility of circulating-tumor DNA (ctDNA)-based genomic and fragmentome analyses to assess the risk of recurrence.
Methods: Targeted sequencing was conducted using pre-treatment and on-treatment blood samples from definitive CCRT-treated patients with LD-SCLC (n=50). Based on 12-month recurrence-free survival (RFS), patients were categorized into persistent-response (PeR, n=29) and non-PeR (n=21) groups. Fragmentome analysis was conducted using ctDNA fragments of different lengths: P1 (100-155 bp) and P2 (160-180 bp).
Results: Patients with TP53 (n=15) and RB1 (n=11) mutation in on-treatment samples demonstrated significantly shorter RFS than patients with wild-type (WT) (P=0.05, P=0.0014, respectively). Fragmentome analysis of all available on-treatment samples (n=26) revealed that the non-PeR group (n=10) had a significantly higher P1 range (P=0.003) and lower P2 range (P=0.002). The areas under the curves for P1, P2, and the fragmentation ratio (P1/P2) in distinguishing the PeR and non-PeR were 0.850, 0.725, and 0.900, respectively. Using optimal cut-off, longer RFSs were found with the low-fragmentation-ratio group than with the high-fragmentation-ratio group (not reached vs. 7.6 months, P=0.002). Patients with both WT RB1 and a low-fragmentation-ratio (n=10) showed better outcomes than patients with both mutated RB1 and a high-fragmentation-ratio (n=10; hazard ratio, 7.55; 95% confidence interval: 2.14-26.6; P=0.002).
Conclusions: RB1 mutations and high fragmentation ratios correlated with early disease recurrence. Analyzing ctDNA could help in predicting early treatment failure and making clinical decisions for high-risk patients.
Keywords: Cell-free DNA (cfDNA); fragmentome; limited disease (LD); small cell lung cancer (SCLC).
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