Pre-operative lymph node staging in localized esophageal cancer using a high-sensitivity ctDNA assay.

e16111 Background: Accurate lymph node (LN) staging remains essential in esophageal cancer (EC) treated with neoadjuvant chemoradiotherapy (CRT) followed by surgery. Circulating tumor DNA (ctDNA) offers a non-invasive measure of tumor burden and may complement imaging-based staging. We evaluated whether an ultrasensitive, tumor-informed ctDNA assay at diagnosis and its dynamics during CRT correlate with clinical and pathological nodal status, and whether ctDNA predicts recurrence-free survival (RFS). Methods: This retrospective analysis includes the first 32 patients from a multicenter prospective observational study (target n = 250). Patients had localized EC (ESCC n = 8; EAC n = 24), received CRT and were staged with PET-CT and, when indicated, laparoscopy. Plasma was collected at baseline, after CRT, and post-operatively. ctDNA was quantified using NeXT Personal, a whole-genome, tumor-informed assay leveraging up to ~1,800 patient-specific variants (limit of detection ~1 PPM). ctDNA dynamics were assessed using the post-CRT/baseline ratio. Associations with clinical staging (cT/cN), pathological outcomes (ypT/ypN), and RFS were evaluated using non-parametric tests and landmark Kaplan–Meier analyses. Results: ctDNA was detectable at diagnosis in all evaluable patients (100% pre-treatment sensitivity). Baseline ctDNA levels were significantly higher in cN-positive vs. cN-negative patients (median 1,580 vs. 58 ppM; p = 0.034). The ctDNA post-CRT/baseline ratio correlated with both pathological tumor stage (ypT; ρ = 0.38, p = 0.046) and pathological nodal stage (ypN; ρ = 0.45, p = 0.015), indicating that limited ctDNA decrease during CRT is associated with persistent nodal disease at surgery. Among ctDNA-negative patients after CRT (n = 18) who proceeded to surgery, only 1 patient harbored ypN+ disease (6%). 6/12 patients with persistently detectable ctDNA after CRT were ypN+ (50%). Notably, ctDNA negativity after CRT and before surgery was significantly prognostic of RFS (HR: 3.9, log-rank P = 0.04), and stratified patients by RFS more effectively compared with pathological complete response (pCR, HR: 2.5, log-rank P = 0.2). Furthermore, persistent ctDNA detection after surgery was also associated with inferior RFS (HR: 10.9, log-rank p≈2.2×10⁻⁶) with a median follow-up of 25.1 months. Conclusions: In this cohort of esophageal cancer patients treated with CRT and surgery, ctDNA PPM quantity at diagnosis correlated with clinical LN involvement and persistent ctDNA after CRT. CRT indicated a high likelihood of residual nodal involvement in the resection specimen. Conversly, ctDNA clearance after CRT was associated with a very low likelihood of ypN-positive disease and a limited residual primary tumor burden, which—if confirmed in larger cohorts—may open opportunities for organ-preserving strategies, addressing a current unmet need in esophageal cancer.