The primary objective of this study is to explore the efficacy and safety of adaptive therapy in the treatment of post-second-line metastatic breast cancer.

This is a phase II, prospective, single arm clinical trial. The objective of the study is to evaluate the efficacy and safety of adaptive therapy in the treatment of post-second-line advanced breast cancer. The therapy regimen primarily including Gemcitabine, Vinorelbine, or Eribulin, will be selected by the investigator based on current guidelines, available treatments, and an assessment of the patient's clinical status, preferences, and financial situation. This study plans to recruit 10 subjects.

Inclusion Criteria:

• Understands and voluntarily signs the informed consent form.
• Minimum life expectancy 16 weeks.
• Histologically or cytologically confirmed advanced invasive breast cancer.
• Histological type: human epidermal growth factor receptor 2 (HER2) negative.
• Prior failure of at least first-line treatment for metastatic disease.
• At least 1 measurable lesion as defined by Response Evaluation Criteria in Solid Tumors (RECIST) criteria.
• Adequate organ function including bone marrow, renal function, hepatic function, and cardiac reserve.
• Premenopausal women must use medically acceptable contraception during the study.
• Compliance with the study protocol.

Exclusion Criteria:

• Pregnant or breast feeding.
• Uncontrolled medical problems.
• Evidence of active acute or chronic infection.
• Hepatic, renal, cardiac, or bone marrow dysfunction.
• Concurrent malignancy or history of other malignancy within the last five years.
• Patients were unable or unwilling to comply with program requirements.
• Concurrent use of any other anti-cancer therapy.