A Study of BEBT-209 Plus Chemotherapy in Patients With Locally Advanced or Metastatic Triple-Negative Breast Cancer

Title: A Study to See if BEBT-209 Combined With Chemotherapy Works to Treat People With Triple-Negative Breast Cancer Researchers want to learn if a new drug called BEBT-209 works to treat people with a specific type of breast cancer. This cancer is called locally advanced or metastatic triple-negative breast cancer (TNBC). The study has two parts. In the first part, researchers want to see if the new drug combination can shrink tumors. In the second part, researchers want to see if this treatment helps people live longer. Researchers will put participants into two groups by chance. This is like flipping a coin. Group 1: Participants get BEBT-209 plus two chemotherapy drugs. These drugs are Carboplatin and Gemcitabine. Group 2: Participants get only the two chemotherapy drugs. Researchers will group people based on the treatments they had in the past. Researchers will also check: How long the treatment keeps the cancer from growing. This is called progression-free survival (PFS). If the treatment is safe. Researchers will look for adverse events (AE), such as low blood cell counts. How participants feel. This is called health-related quality of life (HRQoL). How the body uses the drug.

Inclusion Criteria Participants must meet all of the following criteria to be eligible for the study: 1. Age and gender: Female, aged 18 to 75 years (inclusive). 2. Informed consent: Voluntarily signed the written informed consent form (ICF). 3. Diagnosis: Pathologically confirmed hormone receptor (HR)-negative and human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic triple-negative breast cancer (TNBC). 4. HR-negative: \6 months prior to first metastatic relapse). 3. Central nervous system (CNS) metastases: Known CNS metastases or leptomeningeal disease (including leptomeningeal metastases, spinal cord metastases, spinal cord compression, and unstable brain metastases). Participants with stable brain metastases (clinically/radiographically stable for at least 4 weeks) are eligible. 4. Pulmonary conditions: Clinically significant pulmonary diseases (e.g., pulmonary embolism within 3 months, severe asthma, severe chronic obstructive pulmonary disease (COPD), restrictive lung disease, significant pleural effusion) or autoimmune/inflammatory diseases with lung involvement. Current interstitial lung disease (ILD)/pneumonitis requiring systemic steroids, or active ILD/pneumonitis suggested by baseline imaging. 5. Effusion and cachexia: Uncontrolled moderate to large pleural, pericardial, or abdominal effusion requiring repeated drainage, or cachexia. 6. Transplantation: Prior history of hematopoietic stem cell or bone marrow transplantation. 7. Prohibited concomitant medications (within 7 days prior to first dose): (1) Strong cytochrome P450 3A4 (CYP3A4) inhibitors or inducers; (2) Medications known to significantly prolong the QT interval or cause torsades de pointes (e.g., quinidine, disopyramide, procainamide, sotalol). 8.Washout periods for prior anti-tumor therapy: Radiotherapy or oral small-molecule targeted therapy within 14 days; cytotoxic chemotherapy within 21 days; systemic anti-tumor therapies (e.g., macromolecules, immune checkpoint inhibitors, antibody-drug conjugates (ADCs)) within 28 days; cell therapy within 3 months. 9.Hypersensitivity: Known or suspected hypersensitivity to BEBT-209, carboplatin, gemcitabine, or any of their excipients. 10.Cardiac abnormalities: Significant electrocardiogram (ECG) abnormalities: QTcF \> 480 msec (based on the mean of triplicate ECGs if the first is \>480 msec); History of long QT syndrome (personal or family); Clinically significant ventricular arrhythmia or current use of anti-arrhythmic drugs/implantable cardioverter-defibrillator (ICD). 11.Electrolyte imbalance: Uncontrolled electrolyte disturbances (e.g., hypocalcemia \