The study is an open, prospective study to collect data on the efficacy and safety of T-DXd (DS8201) in Chinese patients with HER2 overexpressing and HER2 underexpressing advanced breast cancer in actual clinical practice in China.

Cohort A:

HER2 overexpressing patients with advanced breast cancer

Cohort B:

HER2 underexpressing patients with advanced breast cancer A total of 400 subjects will be enrolled in the program, with 200 enrolled in Cohort A and 200 enrolled in Cohort B. The study will be conducted by a physician in accordance with current clinical practice. The treatment plan will be recommended to the subjects by the treating physician based on the current clinical practice guidelines in conjunction with the clinical practice, and the patient's decision to be treated with T-DXd (DS8201) should precede enrollment in this study. Because of the non-interventional nature of this study, this study does not alter or interfere with clinician treatment decisions, and the actual medical practice of patients.

Inclusion in the study after the first treatment with the drug is based on inclusion/exclusion criteria. Subject enrollment in this study should be within 2 months of the subject's first dose of medication and prior to the first efficacy assessment. Demographic data, past medical and treatment history, ECOG score, vital signs + physical examination, laboratory tests, objective tumor evaluation, coadministration/concomitant therapy, adverse events, time to progression/death, and subsequent antitumor therapy were collected at baseline, during treatment, and at subsequent follow-up. Imaging evaluation was performed according to RECIST 1.1 criteria. Adverse events evaluation criteria were based on NCI-CTCAE version 5.0.

Inclusion Criteria:

1. Must be competent and able to sign and date an Institutional Review Board (IRB) or Ethics Committee (EC)-approved ICF prior to any study-specific procedure or trial.

2. Female patients aged ≥18 years with advanced breast cancer who are adults.

3. Pathologically confirmed breast cancer that meets the following criteria:

   1. unresectable or metastatic, with evidence of recurrent or metastatic disease.
   2. HER2 overexpression, or HER2 hyperexpression as determined by the central laboratory in accordance with the American Society of Clinical Oncology-Society of American Pathologists guidelines.

4. Patients must have measurable lesions according to RECIST 1.1 criteria.

5. Unmenopausal, menopausal, and perimenopausal female patients were allowed to be enrolled.

6. Prior antitumor therapy against recurrent metastatic disease is allowed.

Exclusion Criteria:

1. Early stage breast cancer
2. Patients who do not meet the criteria for HER2 overexpression and HER2 underexpression.
3. Female patients during pregnancy or lactation.
4. Patients deemed unsuitable for enrollment by the investigator.

Patients receiving T-DXd (DS8201) for HER2 overexpression and HER2 underexpression advanced breast cancer in actual clinical practice in China Chinese patients