OBJECTIVES: The goal of this study was to estimate the budget impact of lapatinib with letrozole as a therapy for metastatic breast cancer with HER2+ status into Brazilian Public healthcare system (SUS). METHODS: Epidemiological data were from Ferlay, et al., 2013. Drugs costs were from Health Price Bank (BPS) of Brazilian Ministry of Health (MOH), a public purchasing database. The analysis looked into 5 years under the perspective of MOH. Only drug costs were considered for analysis. We have also performed sensibility analyses, in parameters of prices (ex-factory, Maximum price for MOH, and negotiated prices) and taxes from different states perspectives. RESULTS:  The budget impact was estimated to a population of 86,789, considering 50% limitation (43,395 and 38,293) of women for the 5^th year, , with ages from 50-64 years old, diagnosed with breast cancer HER2 +. The budget impact analysis under the reference case (market share of 100% of letrozol), in five years, would represent U$18 MI, allowing for an annual growth rate of the total number of patients. The adoption of the newer strategy, for the lapatinib and letrozol (3 alternative scenarios lapatinib + letrozol, scenario 1 (25% of market share), scenario 2 (45%) and scenario 3 (65%)), adjusted for the inflation, represent a budget impact of approximately, US$ 941 milhões. This increase of 307% would occur in the 5 years perspective. CONCLUSIONS: Under the perspective of Brazilian SUS the incorporation of lapatinib and letrozol is not recommended due to high budget impact to SUS. Further, cost effectiveness and budget impact studies can give stronger evidence to decision making.