This study was performed to quantify the economic burden and identify drivers of direct costs of mBC. In a retrospective study of a de-identified administrative claims database of privately insured patients, women between 18 and 64 years of age were included if they had at least one claim with a diagnosis of breast cancer and subsequently one or more claims with a diagnosis of secondary malignancy between January 1, 2003 and December 31, 2009. The study sample was further classified into the following subgroups: (1) Endocrine therapy, (2) HER-2 targeted therapy, (3) Concomitant HER-2 targeted and endocrine therapy, (4) Cytotoxic chemotherapy, and (5) No-systemic therapy. Costs for medical resource utilization were calculated on a per patient per month (PPPM) basis. A total of 7,698 mBC patients were identified from 2003 to 2009 with an average age at index of ~52 years, and average follow up of 2.2 years. The average total direct medical costs for 7,698 mBC patients were $9,788 PPPM. Outpatient costs accounted for the majority of overall PPPM costs. Examining the five different mBC therapeutic subgroups revealed that patients who received no-systemic therapy had the highest costs at $13,926 PPPM, while patients who received systemic endocrine therapy had the lowest costs at $5,303 PPPM. This study demonstrated that mBC is associated with substantial healthcare costs in a non-Medicare patient population. Assuming average PPPM costs of $9,788 and an average life expectancy of 2.2 years, the total average expenditure to treat mBC would be ~$250,000 per patient.