This is a single-arm, multicenter, Phase II clinical study aiming to explore the efficacy and safety of Sacituzumab Govitecan combined with Bevacizumab as a second-line or later treatment for patients with metastatic triple-negative breast cancer (mTNBC). The study will be conducted in 6-8 centers in China.

The study is divided into two phases: a Safety Run-in Phase and a Dose Expansion Phase.

In the Safety Run-in Phase (3-12 patients), three dose levels are planned to determine the recommended dose. The starting dose (Level 1) is Sacituzumab Govitecan 10 mg/kg (Days 1, 8) plus Bevacizumab 7.5 mg/kg (Day 1) every 21 days. Based on the occurrence of Dose-Limiting Toxicities (DLT) in the first cycle, the Safety Monitoring Committee (SMC) will decide whether to continue the current dose or de-escalate to Level 2 (Sacituzumab Govitecan 10 mg/kg + Bevacizumab 5 mg/kg) or Level 3 (Sacituzumab Govitecan 7.5 mg/kg + Bevacizumab 5 mg/kg).

In the Dose Expansion Phase, 40-50 patients will be enrolled to receive the combination therapy at the recommended dose determined in the run-in phase. Efficacy will be evaluated every 2 cycles according to RECIST 1.1, and safety will be assessed continuously until disease progression or intolerable toxicity.

Inclusion Criteria:

1. Patients aged > 18 years.
2. Pathologically confirmed recurrent or metastatic Triple-Negative Breast Cancer (TNBC).
3. ER and PR negativity is defined as < 10% expression in tumor cells. HER2 negativity is defined as IHC 0, 1+, or IHC 2+ with FISH negative. Must have received at least one prior systemic therapy in the metastatic setting.
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
5. Life expectancy of more than 3 months.
6. At least one measurable lesion according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.
7. Adequate organ function.
8. Sufficient washout period before screening (3 weeks from last chemotherapy, 4 weeks from last targeted therapy)

Exclusion Criteria:

1. Prior treatment with Sacituzumab Govitecan or Bevacizumab.
2. Uncontrolled central nerve
3. Presence of other primary malignancies.
4. Severe infection, severe cardiac disease, autoimmune disease, or other conditions deemed unsuitable for anti-tumor therapy.