OBJECTIVES: There are few studies of treatment patterns among elderly, newly diagnosed Stage IV breast cancer (BC) patients receiving human epidermal growth factor receptor 2- (HER2-) targeted therapy.   METHODS: Women aged 65+ with an incident diagnosis of Stage IV BC (index) and no history of other cancer were identified from 2006-2010 linked Surveillance, Epidemiology, and End Results (SEER) and Medicare data. Continuous enrollment from 1 year pre-index (baseline) through disenrollment, death, or the end of the data (follow-up) was required.  Patients were required to receive HER2-targeted therapy (trastuzumab or lapatinib) during follow-up.  Treatment therapies during follow-up were evaluated, as was the distribution of treatment combinations.  Initial treatment regimens were evaluated based on the treatment(s) received after index. A 42-day gap in therapy or the addition of a biologic therapy was used as a marker for a subsequent regimen.    RESULTS: