Circulating Tumor DNA Dynamics to Optimize Neoadjuvant Therapy in HER2-Positive and Triple-Negative Breast Cancer

The purpose of this non-interventional, observational study is to evaluate the clinical utility of circulating tumor DNA (ctDNA) utility-specifically how quickly tumor DNA disappears from the bloodstream (ctDNA clearance)-to help monitor and predict treatment responses in patients with breast cancer. The study focuses on patients diagnosed with Stage II to III HER2-positive or Triple-Negative Breast Cancer (TNBC) who are scheduled to receive standard neoadjuvant therapy (systemic treatment administered before surgery). Because these breast cancer subtypes involve different standard treatment regimens, the study prospectively stratifies patients into three distinct treatment cohorts (Cohorts A, B, and C) to match routine clinical practice and align blood sampling with meaningful clinical milestones.