OBJECTIVES: Considering the increasing number of treatment options for metastatic breast cancer (MBC), it is important to develop high-quality methods to assess the cost-effectiveness of new anticancer drugs. This study aims to develop a global economic model that could be used as a benchmark for the economic evaluation of new therapies for MBC. METHODS: The Global Pharmacoeconomics of Metastatic Breast Cancer (GPMBC) model is a Markov model that was constructed to estimate the incremental cost per quality-adjusted life years (QALY) of new treatments for MBC from a Canadian healthcare system perspective over a lifetime horizon. Specific parameters included in the model are cost of drug acquisition, survival outcomes, and incidence of treatment-related adverse events (AEs) whereas global parameters are patient characteristics, health states utilities, disutilities and costs associated with treatment-related AEs, as well as costs associated with drug administration, medical follow-up, and end-of-life care. The GPMBC model was tested and validated in a specific context, by assessing the cost-effectiveness of lapatinib plus letrozole compared with other widely used first-line therapies for postmenopausal women with hormone receptor-positive (HR+) and epidermal growth factor receptor 2-positive (HER2+) MBC. RESULTS: When validated, the GPMBC model leaded to incremental cost-utility ratios of CA$131,811 per QALY, CA$56,211 per QALY, and CA$102,477 per QALY for the comparison of lapatinib plus letrozole vs. letrozole alone, trastuzumab plus anastrozole, and anastrozole alone, respectively. Results of the model validation were quite similar to those obtained by Delea et al., who also assessed the cost-effectiveness of lapatinib in combination with letrozole in HR+/HER2+ MBC in Canada, thus suggesting that the GPMBC model can replicate results of well-conducted economic evaluations. CONCLUSIONS: The GPMBC model can be very valuable as it allows a quick and valid assessment of the cost-effectiveness of any new treatments for MBC in a Canadian context.