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

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 ormetastatic/recurrent lesion;

• Measurable lesions with treatment response results that can be evaluated throughimaging examinations;

• Able to follow up with the latest progression-free survival or overall survival.

Exclusion Criteria:

• Patients with missing basic clinical information or HER2 immunohistochemistrystaining information;

• Patients with missing pathological results for both primary and metastatic/recurrentlesions;

• 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.