Optimal Application Timing of ADC Drugs for Advanced Breast Cancer

Inclusion criteria

• Female patients aged 18-75 years;
• Histologically confirmed advanced HER2-negative breast cancer, including IHC 2+/ISH-, IHC 1+/ISH-, and IHC 0/ISH- subtypes;
• Completed first-line combination chemotherapy for advanced/metastatic disease (specific regimen not restricted), with disease progression (PD) evaluated per RECIST criteria (HR-positive patients must have received at least one line of endocrine therapy);
• Electrocorticography (ECOG) performance status < 2;
• Estimated life expectancy ≥ 12 weeks;
• Adequate bone marrow function, defined as:

• ANC ≥ 1.5 × 10⁹/L
• Platelets ≥ 90 × 10⁹/L
• Hemoglobin ≥ 90 g/L
• Adequate hepatic and renal function, defined as:

• Total bilirubin ≤ 1.5 × upper limit of normal (ULN)
• AST or ALT ≤ 2.5 × ULN (≤ 5 × ULN for patients with liver metastases)
• Creatinine clearance ≥ 60 mL/min
• Signed informed consent obtained prior to any study-related procedures or treatments, confirming the patient's willingness to participate and comply with study requirements.

Exclusion criteria

• Prior treatment with an ADC after disease recurrence or metastasis;
• Pregnant or breastfeeding women;
• No evaluable recurrent or metastatic lesions as defined by RECIST 1.1 criteria;
• Symptomatic brain parenchymal and/or leptomeningeal metastases with symptoms not adequately controlled by treatment;
• History of other malignancies within the past 5 years, except for adequately treated carcinoma in situ of the cervix, cutaneous squamous cell carcinoma, or well-controlled localized basal cell carcinoma of the skin;
• Psychiatric disorders or other conditions that may interfere with patient compliance;
• Recent history of serious and uncontrolled systemic diseases, such as clinically significant cardiovascular disease, pulmonary disease, metabolic disorders, or arterial/venous thromboembolic events;
• Concurrent use of other investigational drugs, or participation in another clinical trial within 30 days prior to enrollment;
• Known or suspected allergy to any study drug or its excipients;
• Any other condition that, in the opinion of the investigator, renders the patient unsuitable for participation in this trial.