This is a real-world observational study aiming to evaluate the effectiveness of post-progression treatment strategies in patients with advanced breast cancer who have developed resistance to prior targeted therapies, including CDK4/6 inhibitors, PIK3CA inhibitors, trastuzumab deruxtecan (T-DXd), or other targeted agents commonly used in clinical practice. As resistance to these therapies becomes increasingly common, optimal sequencing strategies for subsequent treatment remain unclear.
This study will collect clinical information on post-resistance systemic treatments and their outcomes, including progression-free survival, overall survival, and response rate. Baseline patient and tumor characteristics will also be collected to explore potential prognostic and predictive factors and to develop outcome prediction models that may help guide future clinical decision-making.
This is a non-interventional study based on retrospective and prospective data from routine medical care. The results are expected to provide real-world evidence to inform personalized treatment strategies for patients with advanced breast cancer following resistance to targeted therapies.
Adults (≥18 years old) with histologically or cytologically confirmed advanced or metastatic breast cancer
Received prior treatment with at least one of the following: CDK4/6 inhibitors, PIK3CA inhibitors, trastuzumab deruxtecan (T-DXd), or other targeted therapies
Documented disease progression following prior targeted therapy
Initiated a subsequent line of systemic therapy (chemotherapy, endocrine therapy, targeted therapy, or combination) after resistance
Incomplete medical records or missing key clinical follow-up data
Concurrent diagnosis of other active malignancies (except non-melanoma skin cancer or in situ cervical cancer)
Known central nervous system disease requiring immediate local treatment (unless clinically stable)
Poor general condition with an Eastern Cooperative Oncology Group (ECOG) performance status ≥2