A real-world, multicenter, prospective study to evaluate the patient-reported outcome in Chinese patients who received sacituzumab govitecan or chemotherapy of the physician's choice for metastatic breast cancer progressing on first-line treatment

Inclusion Criteria:

1. Patients aged 18 to 75 years.
2. Patients have been diagnosed with metastatic HER2 negative breast cancer. HER2 status were determined locally by immunohistochemistry (IHC) of patients' primary or metastatic tumor sections. HER2-negative status was defined by IHC staining 0 to 1+ or fluorescence in situ hybridization ratio <2.0 if IHC 2+ or IHC not performed.
3. The metastatic disease was confirmed by clinical, imaging, histological, or cytological measures, including unresectable locally advanced breast cancer, de novo stage IV breast cancer, and recurrent metastatic breast cancer.
4. ECOG-PS ≤2
5. For patients with triple-negative breast cancer (TNBC): at least 1 line of systemic therapy in the metastatic setting; for patients with HR+/HER2- breast cancer: prior treatment with endocrine therapy and CDK4/6 inhibitors, and at least 1 line of systemic therapy in the metastatic setting.
6. At least one evaluable lesion by CT or MRI according to RECIST 1.1.
7. Willing to accept the treatment by the investigator based on the patient's preference, physical condition, prior treatment history, and financial circumstances.
8. Willing to use contraceptive measures during the study period.
9. Willing and able to complete electronic questionnaires/scales on a smartphone, tablet, or other electronic device.
10. All patients can provide an informed consent before enrolment and data collection.

Exclusion Criteria:

1. Insufficient bone marrow, hepatic, or renal function, defined as:

   • Bone marrow: White blood cell count < 3.0 × 10⁹/L, or absolute neutrophil count < 1.5 × 10⁹/L, or platelet count < 75 × 10⁹/L, or hemoglobin < 8.0 g/dL.
   • Hepatic function: Total bilirubin > 1.5 × upper limit of normal (ULN), or ALT/AST > 3.0 × ULN (or > 5.0 × ULN in the presence of liver metastases).
   • Renal function: Serum creatinine > 1.5 × ULN, or creatinine clearance < 50 mL/min.

2. History of other malignancies or hematologic malignancies.

3. Hypersensitivity to the study treatment drugs.

4. Systemic anti-tumor therapy (including chemotherapy, radiotherapy, immunotherapy, etc.) within 2 weeks prior to study drug administration.

5. Treatment with an investigational product within 4 weeks before the first treatment.

6. Presence of any toxicity from prior therapy (excluding alopecia) ≥ Grade 2 according to CTCAE version 5.0, prior to study drug administration.

7. Systemic inflammatory diseases, including but not limited to systemic lupus erythematosus, juvenile chronic arthritis, spondyloarthropathy, Crohn's disease, ulcerative colitis, psoriatic arthritis, or active vasculitis.

8. Severe psychiatric or neurological disorders, including but not limited to schizophrenia, depression, mania, Alzheimer's disease, myasthenia gravis, seizure disorders, or known conditions that may provoke seizures.

9. Pregnant or breastfeeding women.

TNBC