OBJECTIVES: Trastuzumab, a monoclonal antibody, is administered intravenously as monotherapy or in combination with chemotherapy in patients with metastatic breast cancer (MBC) whose tumors over express HER2. This study assessed the cost components of providing trastuzumab-based combination IV therapies to women with MBC. METHODS: An administrative claims database of >60 multi-specialty medical practices/clinics in the US was used to identify women with MBC (ICD-9 code 174 including 196 -198) between January 01, 2003 and May 31, 2006 and receiving trastuzumab plus another IV therapy. Allowable amounts for a claim, which closely represents the actual payments to providers, were used to estimate costs cost per IV administration visit. Billable cost components were categorized based on published literature. RESULTS: A total of 151 patients with 1292 clinic visits receiving any of 7 trastuzumab-based combination IV therapies were identified. The total mean cost per visit across all trastuzumab-based combinations was $3511 of which 70% was accounted for by drugs, 11% by administration of the IV and 19% for other visit-related services, which include supplies and equipment, evaluation and management services, and other concomitantly administered IV or oral drugs. Trastuzumab plus paclitaxel was the most commonly used combination with non-drug costs accounting for 32% ($1072) of total costs ($3341) per visit. The non-drug costs associated with administration of the second most commonly used combination, trastuzumab plus vinorelbine, were 24% ($612) of total costs ($2563) per visit. CONCLUSION: Excluding drug costs, costs associated with IV administration of trastuzumab-based combination therapies and other visit-related services are approximately 30% of total costs. Effective oral therapies for treatment of breast cancer could help offset some of these costs in addition to providing patient benefits such as fewer clinic visits for IV administration.