Second, the 15-year span of patient inclusion was very long; but the patients in different treatment era between the two groups were comparable, and the influences of the changes in the diagnosis and treatment of BC over this period between the two groups were similar, e.g. the proportion of the patients who had HER2 - positive disease but did not received trastuzumab-targeted therapy was comparable after IPTW between the two groups. Here, ERBB2 is linked to breast cancer.