This study is a multicenter, double-cohort clinical research aimed at systematically evaluating the value of jointly detecting the HER2 expression of CTCs/CTECs and the serum HER2 ECD level in predicting the efficacy of T-DXd treatment for patients with HER2 low expression (IHC 1+ or IHC 2+/ISH-) and HER2 IHC 0 advanced breast cancer.
Patients with a pathological record of breast cancer;
Group A: Diagnosed with low expression of HER2 (IHC 1+ or IHC 2+ and ISH-); Group B: Diagnosed with HER2 0 expression (IHC 0);
No history of other malignant tumors;
Signed the informed consent form at the age of 18 or above;
1. Male breast cancer patients; 2. Pregnant or breastfeeding; 3. Patients known to have an allergic reaction to the active substances or any excipients of T-DXd; 4. Patients judged by the investigators to be unsuitable to participate in this study.