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

Patients with documented stage II-III HER2+ or TNBC and fit candidates for NAT. 2. In TNBC group, confirmed negative ER, PR and HER2 disease by local testing on primary disease specimen: tumor must be negative ER, PR, and HER2 defined by immunohistochemistry (IHC) according to the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines for hormone receptor testing (Allison et al., 2020; Wolff et al., 2023). 3. In HER2+ group, Confirmed HER2+ disease by local testing on primary disease specimen: tumour must be HER2+ according to ASCO/CAP 2023 guidelines for HER2 testing (Wolff et al., 2023). 4. Patients with measurable disease; Patients with multifocal or multicentric breast cancer with at least one tumor lesion ≥1.0 cm in the longest diameter by ultrasound (reference lesion) are also eligible if the two largest tumor lesions have been histologically confirmed in the clinical evaluation and meet pathological criteria for TNBC and HER2+. 5. No previous treatment of the disease by chemotherapy, hormone therapy, surgery or radiotherapy. 6. Patients with breast cancer are eligible for surgery. 7. Eastern Cooperative Oncology Group (ECOG) performance status≤2.