This study is a multi-center observational real-world study, with a total of 500 patients planned to be enrolled. This study is divided into two cohorts: the triple-negative breast cancer (TNBC) cohort and the hormone receptor-positive/human epidermal growth factor receptor 2-negative breast cancer (HR+/ HER2-BC) cohort. The aim of this study is to assess the efficacy and safety of Sacituzumab Tirumotecan (SKB264) monotherapy or combination therapy in patients with unresectable locally advanced, recurrent or metastatic HER2-negative breast cancer in the real-world setting.

Inclusion Criteria:

1. Aged ≥ 18 years old at the time of signing the informed consent form, regardless of gender;

2. Patient must meet one of the following pathological diagnoses and classifications:

   2.1) For TNBC Cohort: -Histological/cytological confirmed of triple-negative breast cancer (TNBC) from the most recent pre-SKB264 biopsy/pathological report, with: HER2 negative: immunohistochemistry (IHC) of 0 or 1+; if is 2+ by IHC, negative HER2 expression must be confirmed by fluorescence in situ hybridization (FISH); Estrogen and progesterone receptor negative means that less than 1% of the cells express hormone receptors as indicated by IHC; -Locally advanced, recurrent, or metastatic disease (locally advanced disease should be confirmed by investigators as ineligible for curative resection); 2.2) For HR+/HER2- BC Cohort: -Histological/cytological confirmed of HR+/HER2- breast cancer from the most recent pre-SKB264 biopsy/pathological report, with: HER2 negative: IHC of 0 or 1+; if is 2+ by IHC, negative HER2 expression must be confirmed by FISH; HR positive: Hormone receptor-positive (HR, ER, or PR status) was defined as ≥1% expression by IHC.-Locally advanced, recurrent, or metastatic disease (locally advanced disease should be confirmed by investigators as ineligible for curative resection);

3. Plan to receive SKB264 monotherapy or combination therapy;

4. Prior treatment lines: -For TNBC Cohort: ≤2 lines of systemic antitumor therapy for unresectable locally advanced, recurrent, or metastatic disease; -For HR+/HER2- BC Cohort: ≤2 lines of systemic antitumor therapy (excluding endocrine therapy) for unresectable locally advanced, recurrent, or metastatic disease;

5. Voluntarily participate in the study, sign the informed consent form and demonstrate good compliance.

Exclusion Criteria:

1. Patients with other malignancies, except cured basal or squamous cell skin cancer or in situ cancer of cervix; and patients with other malignancies must have a tumor-free period of at least 5 years;
2. Patients who are currently participating in other interventional clinical studies;
3. Known allergy to the investigational drug or any of its components;
4. Pregnant or lactating women;
5. Any situation that the researchers consider to interfere with the evaluation of the study drug or the safety of the subjects or the analysis of the study results, or any other situation that the researchers consider inappropriate to participate in this study.

Patients with Unresectable Locally Advanced, Recurrent or Metastatic HER2-Negative Breast Cancer