Residual circulating tumor DNA after adjuvant chemotherapy effectively predicts recurrence of stage II-III gastric cancer

Abstract

Background: Circulating tumor DNA (ctDNA) is a promising biomarker for predicting relapse in multiple solid cancers. However, the predictive value of ctDNA for disease recurrence remains indefinite in locoregional gastric cancer (GC). Here, we aimed to evaluate the predictive value of ctDNA in this context.

Methods: From 2016 to 2019, 100 patients with stage II/III resectable GC were recruited in this prospective cohort study (NCT02887612). Primary tumors were collected during surgical resection, and plasma samples were collected perioperatively and within 3 months after adjuvant chemotherapy (ACT). Somatic variants were captured via a targeted sequencing panel of 425 cancer-related genes. The plasma was defined as ctDNA-positive only if one or more variants detected in the plasma were presented in at least 2% of the primary tumors.

Results: Compared with ctDNA-negative patients, patients with positive postoperative ctDNA had moderately higher risk of recurrence [hazard ratio (HR) = 2.74, 95% confidence interval (CI) = 1.37-5.48; P = 0.003], while patients with positive post-ACT ctDNA showed remarkably higher risk (HR = 14.99, 95% CI = 3.08-72.96; P < 0.001). Multivariate analyses indicated that both postoperative and post-ACT ctDNA positivity were independent predictors of recurrence-free survival (RFS). Moreover, post-ACT ctDNA achieved better predictive performance (sensitivity, 77.8%; specificity, 90.6%) than both postoperative ctDNA and serial cancer antigen. A comprehensive model incorporating ctDNA for recurrence risk prediction showed a higher C-index (0.78; 95% CI = 0.71-0.84) than the model without ctDNA (0.71; 95% CI = 0.64-0.79; P = 0.009).

Conclusions: Residual ctDNA after ACT effectively predicts high recurrence risk in stage II/III GC, and the combination of tissue-based and circulating tumor features could achieve better risk prediction.

Keywords: chemotherapy; ctDNA; gastric cancer; postoperative; recurrence.

FIGURE 1

Flowchart of patient selection and sample collection. Abbreviations: HAS, hepatoid adenocarcinoma of the stomach; GASC, gastric adenosquamous carcinoma; ACT, adjuvant chemotherapy; STAD, stomach adenocarcinoma; ctDNA, circulating tumor DNA; pos, positive; neg, negative.

FIGURE 2

Genomic profiling of the most commonly mutated genes (mutation frequency ≥5%) presented in the primary gastric tumors, and the corresponding clinicopathological features and biomarker status. Abbreviations: AD, adenocarcinoma; SRCC, signet ring cell carcinoma; ctDNA, circulating tumor DNA; Pre‐op, preoperative; Post‐op, postoperative; ACT, adjuvant chemotherapy; CA, cancer antigen, including CEA, CA72‐4, CA199.

FIGURE 3

Prognostic value of postoperative and post‐adjuvant chemotherapy ctDNA. (A, B) Kaplan–Meier estimates of recurrence‐free survival (RFS) and overall survival (OS) among patients evaluated for postoperative ctDNA. (C, D) Kaplan–Meier estimates of RFS and OS among patients evaluated for post‐ACT ctDNA. P value was calculated using a two‐sided log‐rank test. Abbreviations: ctDNA, circulating tumor DNA; HR, hazard ratio; CI, confidence interval; ACT, adjuvant chemotherapy.

FIGURE 4

Performance of recurrence prediction across different biomarkers. (A‐C) The bar plot depicts the association between different biomarkers (A, postoperative ctDNA; B, post‐ACT ctDNA; C, postoperative serial cancer antigen) and recurrence status. P value was calculated using a two‐sided Fisher's exact test. (D) Performance measurements of postoperative, post‐ACT ctDNA status, and postoperative serial cancer antigen (i.e., CEA, CA199, CA72‐4) demonstrated by sensitivity, specificity, accuracy, PPV and NPV. Abbreviations: ctDNA, circulating tumor DNA; pos, positive; neg, negative; ACT, adjuvant chemotherapy; CA, cancer antigen, indicated CEA, CA72‐4, CA199; PPV, positive predictive value; NPV, negative predictive value.

FIGURE 5

ctDNA after definitive treatment improved model's performance for RFS prediction. (A) The nomogram was constructed by selected clinicopathological factors, ERBB4 mutational status, and ctDNA status (post‐operation or post‐ACT if available) for predicting 2‐year and 3‐year RFS. mut, mutant; wt, wild‐type; pos, positive; neg, negative. (B) Comparison of C‐index and 95% CI for predicting RFS between the model with and without ctDNA status. (C) Time‐dependent ROC curves and corresponding AUC values of 2‐year (left) and 3‐year (right) RFS prediction among the model with and without ctDNA status. Abbreviations: RFS, recurrence‐free survival; ctDNA, circulating tumor DNA; ROC, receiver operating characteristic; AUC, area under the curve; AJCC, American Joint Committee on Cancer.