ERBB2 and breast cancer: Similarly, trastuzumab duocarmazine showed an ORR of 28% (95% CI 13.8–46.8) in patients with HER2-low/HR+ MBC (n = 32) and of 40% (95% CI 16.3–67.6) in patients with HER2-low/HR- breast cancer in phase I [12].