Although trastuzumab-based therapy is considered the standard of care among patients with early or metastatic HER2-positive breast cancer, observational studies on real-world treatment patterns suggest that 12% to 54% of patients across regions of United States, Europe and China did not receive trastuzumab or any other HER2-targeted agent as first and/or later line treatment. Here, ERBB2 is linked to breast cancer.