Other outpatient care, which included systemic and anticancer treatments administered in the outpatient setting, accounted for the largest component of total all-cause and breast cancer-related expenditures in HER2-targeted and no HER2-targeted cohorts (48.6% of total breast cancer-related costs for HER2-targeted agent users and 48.1% for no HER2-targeted agent users), while inpatient costs were the largest cost component for no treatment patients. Here, ERBB2 is linked to breast cancer.