Evaluate the efficacy and safety of T-DXd in patients with HER2-positive and HER2-low metastatic breast cancer

The DESTINY-Breast trials established trastuzumab deruxtecan (T-DXd) as a treatment significantly improving outcomes in human epidermal growth factor receptor 2 (HER2)-positive and HER2-low metastatic breast cancer (MBC). However, real-world effectiveness is susceptible to confounding factors. This multicenter, real-world study aims to systematically evaluate the efficacy and safety of T-DXd in patients with HER2-positive and HER2-low MBC. Key clinicopathological parameters were to be integrated to develop an individualized prognostic prediction model, facilitating precision medicine implementation in clinical practice.

Inclusion Criteria:

1. female patients aged ≥18 years;
2. histologically confirmed HER2-positive (IHC 3+ or IHC 2+/FISH+) or HER2-low (IHC 1+ or IHC 2+/FISH-) disease;
3. radiologically confirmed recurrent or metastatic disease;
4. completion of ≥2 cycles of T-DXd therapy;
5. comprehensive medical documentation;
6. Eastern Cooperative Oncology Group (ECOG) performance status ≤3;
7. measurable target lesions according to RECIST 1.1

Exclusion Criteria:

1. history of interstitial lung disease
2. incomplete medical records
3. concurrent malignancies;
4. pregnancy or lactation
5. psychiatric disorders compromising treatment adherence

Patients with HER2-positive or HER2-low expressing, locally advanced or metastatic breast cancer were eligible and received therapy. DXd was administered intravenously at 5.4 mg/kg every 3 weeks (21-day cycles) until disease progression or unacceptable toxicity. Dose adjustments were performed according to clinical status and treatment tolerance. Complete blood count with hepatic and renal function parameters were monitored before each cycle. Tumor response assessment via RECIST 1.1 criteria was conducted radiologically every two cycles.