OBJECTIVES: Although higher density chemotherapy regimens could improve treatment outcomes, febrile neutropenia and its related complications often limit the density of chemotherapy administration to a suboptimal level. Filgrastim-enabled chemotherapy regimens administered at a high density were shown to increase survival among breast cancer patients in a recent clinical trial (Citron et al, 2003). The high costs of filgrastim and time loss of patients and caregivers due to frequent administration, motivated an economic analysis to compare the cost-effectiveness of dose-dense therapy with filgrastim vs. conventional chemotherapy in breast cancer patients. METHODS: Target Population: Women with node-positive breast cancer. Time Horizon: Twelve cycles of chemotherapy with lifetime follow up. Perspective: Societal. Data Sources: The Intergroup Trial C9741 was the primary source of treatment efficacy, rates of febrile neutropenia with and without hospitalization, and other major toxicities. Direct health care cost components and indirect costs of patient and caregiver time loss were obtained from literature review. Measurements: Discounted lifetime costs were estimated based on a decision model. Discounted quality-adjusted life years (QALYs) was estimated based on the DEALE method. Incremental cost-effectiveness ratios (ICERs) were calculated for each age group at 5-year interval. RESULTS: Under the base case assumptions, dose-dense chemotherapy incurred cost $25,530 higher than conventional therapy over lifetime, and the average discounted survival benefits were 1.400 QALYs per patient. This resulted in an average cost-effectiveness ratio of $19,940 per QALY saved. ICERs were $13,672/QALY in age group 30-34, and this ratio increased with age to $34,418 /QALY in age group 75-80, indicating a more favorable cost-effectiveness in younger women. Results of the model were relatively stable when the parameters changed within a reasonable range. CONCLUSIONS: From a societal prospective, dose-dense chemotherapy with filgrastim in breast cancer patients is a cost-effective improvement compared to conventional chemotherapy.