Case Report: Trastuzumab deruxtecan combined with fulvestrant in a patient with HR+/HER2-low metastatic breast cancer.

Breast cancer is the most common malignancy among women worldwide, and hormone receptor-positive (HR+)/human epidermal growth factor receptor 2 (HER2)-low breast cancer poses significant challenges once resistance to endocrine therapy and CDK4/6 inhibitors develops. We present a 45-year-old female patient with HR+/HER2-low metastatic breast cancer who progressed on standard-of-care treatments. The combination of trastuzumab deruxtecan and fulvestrant demonstrated significant clinical efficacy and favorable tolerability, achieving a progression-free survival of 26 months with no grade 3 or higher adverse events observed. This case suggests that this combination may represent a promising therapeutic strategy for patients with advanced, treatment-refractory HR+/HER2-low breast cancer, offering a useful reference for clinical practice.