Résumé : Background The development of trastuzumab is considered to be one of the greatest improvements in breast cancer treatment in recent years. This study aims to evaluate changes in the uptake of trastuzumab over the last 12 years and to determine whether its use is proportional to patient needs in the European Union and the USA. Methods Using national registry data, the number of new cases of HER2-positive breast cancer patients per year was estimated. The number of likely trastuzumab treatments per year was estimated using trastuzumab procurement data for each country. Results Western Europe and the USA show increasing procurement level of trastuzumab over the years studied, reaching proportional of use of trastuzumab few years after its marketing authorization in the early 2000's. After the approval in the adjuvant setting, in the year 2006, it was observed underuse of trastuzumab given the increase of the number of patients in need of treatment. Proportional use was shortly met after a couple of years. Few countries in Eastern Europe acquired the needed quantity of trastuzumab, with procurement levels starting to increase only after approval in the adjuvant setting in 2006. Conclusion Significant differences in trastuzumab procurement are observed between Western Europe, the USA and Eastern Europe, with the latter geographic region acquiring insufficient amounts of the drug required to treat all patients in need.