This Phase Ib/IIa study is evaluating the safety, tolerability, pharmacokinetics, and preliminary efficacy of MR001 in patients with advanced triple-negative breast cancer (TNBC) who have progressed after prior therapy.

This is a dual-cohort, open-label, dose escalation and dose expansion Phase Ib/IIa study to evaluate the safety, tolerability, pharmacokinetics, and preliminary anti-tumor activity of MR001 in patients with locally recurrent or metastatic advanced triple-negative breast cancer (TNBC) who have progressed after first-line or later-line therapy.

Inclusion Criteria:

• Patients with histologically or cytologically confirmed triple-negative breast cancer (TNBC).
• Subjects with locally recurrent or metastatic advanced TNBC who have progressed after first-line or later-line therapy.
• Presence of at least one measurable lesion according to RECIST V1.1 criteria.
• ECOG Performance Status 0 or 1.
• Life expectancy >3 months.
• Adequate organ and hematopoietic function based on the laboratory tests.
• Voluntarily sign the informed consent form.

Exclusion Criteria:

• History of severe allergy or hypersensitivity to the investigational product or its excipients or drugs of similar chemical class (e.g., monoclonal antibodies), or contraindications to the investigational product.
• Requirement for systemic immunosuppressive therapy within 14 days prior to the first dose of study drug or during the study.
• Major surgery (excluding puncture biopsy) within 4 weeks prior to the first dose of study drug, or anticipated need for major surgery during this study.
• Uncontrolled active brain metastases or leptomeningeal metastasis.
• History of autoimmune disease requiring treatment with corticosteroids or immunosuppressive drugs.
• Women in the period of preconception, pregnancy, or lactation.
• Any other circumstances which the investigator considers may increase risks to subjects or interfere with the results of the trial.