Abstract
BACKGROUND: The potential of circulating tumour DNA (ctDNA) as a reliable biomarker for relapse/metastasis early detection and prognosis in esophageal squamous cell carcinoma (ESCC) after radiotherapy/chemoradiotherapy (RT/CRT) initiation requires comprehensive investigation. METHODS: Treatment-naive locally advanced ESCC patients with available baseline plasma samples were prospectively enrolled from November 2018 to January 2020. RT/CRT was delivered with a simultaneous integrated boost of radiation dose. Serial plasma samples were collected at baseline (T(0) ), week 4 of RT/CRT (T(1) ), 1-3 (T(2) ) and 3-6 months post-RT/CRT (T(3) ). ctDNA was analysed using next-generation sequencing of 474 cancer-relevant genes. RESULTS: A total of 128 plasma samples from 40 eligible patients were analysed (median age: 64 [range: 40-78], 88% males, 95% stage III/IV), and the median follow-up time was 20.6 months (range: 12.2-33.3). During the post-RT/CRT surveillance including 36 patients, radiological progression was observed in 16 patients, and 69% (11/16) had detectable post-RT/CRT ctDNA prior to radiological progression, with a median lead time of 4.4 months compared with radiological imaging. ctDNA positivity at T(1) (hazard ratio, HR: 3.60, 95% confidence interval, CI: 1.30-10.01) or T(2) (HR: 5.45, 95% CI: 1.72-17.26) indicated inferior progression-free survival (PFS). ctDNA clearance between T(0) -T(1) (HR: 0.31, 95% CI: 0.08-1.13) or T(0) -T(2) (HR: 0.11; 95% CI: 0.02-0.61) was associated with relatively favourable PFS. Similar results were obtained when focusing on patients without esophagectomy after RT/CRT. Notably, detectable ctDNA at T(1) was a potential indicator of high local recurrence risks (HR: 4.43, 95% CI: 1.31-15.04). CONCLUSIONS: ctDNA was identified as a robust biomarker for early detection of disease progression and post-RT/CRT prognosis stratification in ESCC. Detectable ctDNA at week 4 of RT/CRT might indicate higher local recurrence risks, implying the potential clinical utility of ctDNA tests in guiding post-RT/CRT treatments for locoregional control in ESCC.