ERBB2 and breast cancer: T-DXd showed unparalleled efficacy in metastatic HER2+ BC previously exposed to other standard anti-HER2 therapies.8-12 Although T-DXd has massively entered our daily practice based on excellent results of prospective clinical trials, the safety, feasibility, and antitumor efficacy of T-DXd in a real-world population of patients with HER2+ mBC remains unknown.