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
Patients with advanced breast cancer who developed resistance to targeted therapies and subsequently received systemic treatment in routine clinical practice. The study population includes diverse subtypes (HR+/HER2-, HER2+, TNBC) and reflects real-world treatment patterns in post-progression settings.
Cohort
Retrospective
Not listed
Progression-Free Survival (PFS)
Progression-Free Survival (PFS) is defined as the time from the initiation of post-progression systemic treatment (after resistance to CDK4/6 inhibitors, PIK3CA inhibitors, T-DXd, or other targeted therapies) to the date of documented disease progression or death from any cause, whichever occurs first. Disease progression will be determined based on radiological or clinical assessment, as per real-world documentation standards. Patients without progression or death at the time of analysis will be censored at the date of last follow-up.
Overall Response Rate (ORR)
ORR is defined as the proportion of patients achieving a complete response (CR) or partial response (PR) to the post-progression systemic treatment, as assessed by the treating physician based on radiological or clinical documentation. Response assessment will follow real-world clinical practice without central review.
Disease Control Rate (DCR)
DCR is defined as the proportion of patients who achieve complete response (CR), partial response (PR), or stable disease (SD) for at least 8 weeks after initiating post-resistance therapy. Evaluations are based on clinical or imaging assessment as documented in routine practice.
Overall Survival (OS)
OS is defined as the time from the initiation of post-resistance systemic therapy to death from any cause. Patients still alive at the time of analysis will be censored at their last known follow-up date.
Treatment-Related Adverse Events
The incidence and type of treatment-related adverse events (AEs) will be collected as documented in the medical record, based on physician assessment. AEs will be classified according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0, where available.
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