This study assessed the clinical value of dynamic plasma circulating tumor DNA (ctDNA) monitoring to evaluate immunotherapy efficacy in advanced esophageal squamous cell carcinoma (ESCC). Patients enrolled in the ORIENT-2 study received second-line sintilimab monotherapy. The primary aim was to determine whether serial ctDNA measures and a computed molecular tumor burden index (mTBI) provide real-time molecular information that correlates with imaging-based response and survival outcomes.
Ninety-four patients with advanced ESCC treated with sintilimab were included. Plasma samples were collected at baseline and after every 2–3 treatment cycles. Targeted sequencing of ctDNA was used to identify somatic variants. The molecular tumor burden index (mTBI) was calculated to quantify ctDNA burden and to track dynamic changes over treatment. Imaging evaluations were performed simultaneously with plasma sampling, and response was assessed by RECIST 1.1.
Of 93 eligible baseline plasma samples, targeted sequencing detected 614 somatic mutations (median 6 mutations per sample). Missense mutations were the most common mutation type. High-frequency mutated genes at baseline included TP53 (82%), CDKN2B (23%), and NOTCH1 (22%). These baseline genomic findings characterized the mutational profile of the cohort prior to continued immunotherapy.
Sixty-eight patients had both baseline and post-2-cycle plasma samples available for comparison. Across these patients, variant allele frequencies (VAFs) of core driver genes showed no significant changes after two cycles (all P > 0.05). Additionally, no newly emerged core driver gene mutations were identified following two cycles of treatment, indicating limited short-term evolution of detected core driver alterations in ctDNA during early sintilimab exposure in this group.
Copy number variation of CCND1 was associated with shorter progression-free survival (PFS) (HR = 1.88, 95% CI: 1.08–3.27). Mutations in other frequently altered genes, including TP53 and NOTCH1, were not associated with PFS (all P > 0.05). None of the frequently mutated genes at baseline were associated with overall survival (OS) (all P > 0.05).
Among the 68 patients with paired samples, 11 (15.9%) achieved ctDNA clearance after two cycles; none of these 11 patients exhibited tumor progression on concurrent imaging. The remaining 57 patients had ctDNA that either became positive or remained persistently positive; of these, 30 (52.6%) showed progression on imaging. The difference in progression rates between patients with ctDNA clearance versus those with positive/persistent ctDNA was statistically significant (P = 0.002). Patients who achieved ctDNA clearance experienced significantly delayed tumor progression compared with patients with positive or persistent ctDNA (HR = 2.05, 95% CI: 1.06–3.96). However, ctDNA status at two cycles did not have a statistically significant impact on OS (HR = 1.38, 95% CI: 0.62–3.09).
After two cycles of treatment, patients categorized in the low mTBI group had a higher disease control rate (DCR) than those in the high mTBI group: 73.5% (25/34) versus 38.2% (13/34), P = 0.007. Low mTBI was also associated with superior PFS (HR = 2.80, 95% CI: 1.65–4.75) and superior OS (HR = 3.54, 95% CI: 1.95–6.42) compared with high mTBI. Dynamic changes in mTBI were noted to be highly consistent with concurrent imaging response assessments.
Patients classified into the molecular response group based on mTBI dynamics had a significantly higher DCR than the non-response group [87.5% (21/24) vs. 42.2% (19/45), P < 0.001], and demonstrated improved PFS (HR = 2.39, 95% CI: 1.41–4.06) and OS (HR = 2.77, 95% CI: 1.46–5.22).
Among 32 patients whose first imaging evaluation after two cycles showed stable disease (SD), those in the molecular response group had comparable PFS to the non-response group (HR = 1.03, 95% CI: 0.51–2.08, P = 0.942). Notably, molecular responders in this SD subgroup had significantly longer OS than non-responders (HR = 3.12, 95% CI: 1.20–8.06), suggesting that mTBI-based molecular response may provide prognostic stratification beyond early radiographic stability.
Dynamic monitoring of ctDNA using a computed mTBI provided real-time and sensitive molecular information that correlated with imaging response and clinical outcomes in advanced ESCC treated with second-line sintilimab. ctDNA clearance and low mTBI after two cycles were associated with improved disease control and delayed progression; molecular response by mTBI correlated with superior PFS and OS. These findings support the potential clinical utility of serial ctDNA and mTBI monitoring for personalized treatment management in advanced ESCC.
Note: The source article did not report additional methodological limitations or detailed analytic parameters beyond those summarized above.