CtDNA for clonal evolution surveillance and therapeutic efficacy prediction in unresectable locally advanced non-small cell lung cancer under radiotherapy.

Abstract

e20555 Background: Therapeutic efficacy differs across unresectable locally advanced non-small cell lung cancer (LA-NSCLC) patients receiving definitive radiotherapy/chemoradiotherapy (RT/CRT), but the underlying resistance mechanism, clonal evolution and molecular prognostic factors remain poorly understood. Methods: Unresectable LA-NSCLC patients treated with definitive RT/CRT were consecutively enrolled between May 2018 and November 2020. Next-generation sequencing covering 474 cancer-relevant genes was performed on plasma ctDNA collected at pre-treatment (TP0), 4-week post-RT (TP1), 1-month post-RT (TP2), 3-month post-RT (TP3), and progression (TP4). Main study endpoints included disease progression, progression-free survival (PFS), death from any cause, overall survival (OS), distant metastasis and distant metastasis free survival. Fisher’s exact test and two-sample t-tests were performed to compare the frequencies and means of independent groups, respectively. The median follow-up time was estimated using the reverse Kaplan-Meier method. Hazard ratios (HR) with 95% confidence intervals (CI) were estimated by Cox proportional hazards models. Results: A total of 46 patients were included (median age: 63 [range: 40–80], males: 87%, clinical stage IIIB: 52%, squamous cell carcinoma: 54%, TP0 ctDNA shedding: 63%, consolidation immunotherapy: 33%). Twenty-nine (63%) patients developed disease progression by the end of follow-up (median follow-up: 23.7 months), with median PFS and OS being 15.5 and 25.4 months, respectively. The polymerase epsilon ( POLE) mutational signature at TP0 indicated inferior PFS (HR: 5.32, 95% CI: 1.83–15.45) and worse OS (HR: 20.68, 95% CI: 3.94–108.62). Notably, newly-discovered/lost mutations were rarely observed at TP4 when compared to TP0. Patients with a high ratio of mean over max variant allele frequency (m/mVAF) in TP0 samples, indicative of a clonal predominant tumor with a low subclone fraction ( P< 0.01), had relatively poor OS, compared to patients with low m/mVAF (HR: 2.92, 95% CI: 0.82–10.46) or undetectable ctDNA (HR: 3.39, 95% CI: 0.98–11.75). The prognostic value was validated in an independent publicly available dataset of 431 LA-NSCLC patients receiving definitive RT/CRT, showing patients with high m/mVAF demonstrated worse OS than those with low m/mVAF (HR: 1.43, 95% CI: 1.08–1.89). Additionally, increased m/mVAF between TP0 and TP1 indicated an elevated risk for disease progression ( vs. non-increase, HR: 3.49, 95% CI: 1.20–10.16), especially for distant metastasis ( vs. non-increase, HR: 2.85, 95% CI: 0.84–9.69). Conclusions: Our findings demonstrated the clinical value of plasma ctDNA and its derived molecular features in delineating clonal evolution, monitoring therapeutic resistance, and predicting prognosis of LA-NSCLC under definitive RT.