Monitoring of circulating tumor DNA in patients with stage II-III breast cancer treated with neoadjuvant chemotherapy

Circulating tumor DNA (ctDNA) has potential as a prognostic factor for predicting relapse in high-risk breast cancer (BC). This study investigates the utility of ctDNA assessment using a tumor-informed assay, in patients with high-risk BC treated with neoadjuvant chemotherapy (NAC). Thirty newly diagnosed patients with various high-risk BC subtypes participated, providing serial blood samples at multiple time points, including baseline, during NAC, and during follow-up. ctDNA was detected at baseline in 29/29 patients for whom an assay panel could be designed, with detection sensitivity reaching 0.0083% (variant allele frequency). Among patients with detectable baseline ctDNA, 94% showed clearance during treatment, correlating with improved outcomes. Additionally, ctDNA detection post-surgery or during follow-up predicted disease recurrence. These findings suggest that serial ctDNA monitoring throughout NAC and follow-up can effectively identify residual disease in BC and correlate with clinical outcomes.