It has been approved in the United States for the treatment of adult patients with unresectable or metastatic hormone receptor (HR)-negative, HER2-low breast cancer, and more recently, for those with unresectable or metastatic HR-positive, HER2-low or HER2-ultralow breast cancer, some of whom would be considered as triple-negative [10, 11]. Here, ERBB2 is linked to breast cancer.