Efficacy of Trastuzumab Deruxtecan in Metastatic Breast Cancer With Different HER2 Expression Patterns

HER2 Heterogeneity and Its Impact on Benefit From Trastuzumab Deruxtecan in Metastatic Breast Cancer

The purpose of this observational study is to learn about the HER2 heterogeneity and its impact on benefit from trastuzumab deruxtecan in metastatic breast cancer. The main question it aims to answer is:

- Does the heterogeneity of HER2 expression level and spatial distribution in different tissues affect the efficacy of trastuzumab deruxtecan in metastatic breast cancer?

Inclusion Criteria:

• Patients with advanced or locally unresectable breast cancer;
• Treated with T-DXd (DS-8201, trastuzumab deruxtecan) regardless of line of therapy, HR, and HER2 expression level;
• HER2 immunohistochemistry staining information of the primary lesion or metastatic/recurrent lesion;
• Measurable lesions with treatment response results that can be evaluated through imaging examinations;
• Able to follow up with the latest progression-free survival or overall survival.

Exclusion Criteria:

• Patients with missing basic clinical information or HER2 immunohistochemistry staining information;
• Patients with missing pathological results for both primary and metastatic/recurrent lesions;
• Patients with no measurable lesions and unable to evaluate T-DXd treatment response;
• Discontinue T-DXd therapy for unacceptable adverse events or other reasons;
• Patients lost to follow-up after T-DXd treatment.