Circulating tumor DNA refines consolidation immunotherapy for limited-stage small cell lung cancer patients

Despite the lack of predictive biomarkers and a prognostic stratification strategy, immune checkpoint inhibitor (ICI) has shown promise in improving outcomes for patients with limited-stage small cell lung cancer (LS-SCLC). We evaluated the potential of circulating tumor DNA (ctDNA) to dynamically predict outcomes in patients with LS-SCLC receiving concurrent chemoradiotherapy (CCRT) with or without consolidation ICI. We analyzed 490 serial samples collected from 144 LS-SCLC patients at baseline (t0), post-induction chemotherapy and pre-thoracic radiotherapy (t1), post-radiotherapy (t2), and progressive disease (t3). For 44 patients receiving consolidation ICI with serplulimab, an investigational PD-1 inhibitor, ctDNA dynamics during consolidation ICI were also assessed at multiple time points. Patients with undetectable ctDNA after CCRT had good outcomes with or without consolidation ICI, whereas ctDNA-positive patients at t2, indicating poor response to CCRT, derived survival benefit from consolidation ICI. Notably, ctDNA status at t1 appeared more predictive than at t2. A three-level risk stratification strategy integrating t1 ctDNA status with radiological tumor shrinkage identified a high-risk subgroup of patients who achieved significantly improved progression-free survival (PFS) (hazard ratio [HR], 0.24; 95% confidence interval [CI], 0.08-0.75; p = 0.014) and overall survival (OS) (HR, 0.06; 95% CI, 0.00-0.42; p = 0.001) from consolidation ICI, prioritizing CCRT plus consolidation ICI. Furthermore, maintaining ctDNA negativity during consolidation ICI was associated with favorable outcomes. These data provide valuable insights into the individualized management of LS-SCLC in the era of immunotherapy.