OBJECTIVES: Recent evidence suggests that many breast cancer patients discontinue their hormonal therapy treatment regimen before the end of the recommended treatment period, but reasons for treatment discontinuation are not well understood. Therefore, we examined reasons for hormonal therapy discontinuation in a European treatment cohort of female breast cancer (BC) patients. METHODS: Female patients ages 21+ with a diagnosis of BC between January 2006 and December 2008 were identified within IMS Oncology Analyzer™ which provides retrospective, cross sectional, cancer-treatment data from 14 countries including France, Germany, Italy, Spain, and the United Kingdom and encompasses over 60,000 de-identified BC patient records from a physician panel of nearly 800 doctors in the EU5. Patients within the EU5 with early stage BC (stages I-IIIa) who received hormonal therapy and for whom their physician provided a reason for discontinuing first course of therapy were included in the study. Patients enrolled in clinical trials were excluded.  Reasons for discontinuation of therapy include course completion, progression of disease, stabilization of disease, adverse events, terminal outlook, poor performance, and patient’s choice. RESULTS: 10,949 patients were identified. Approximately 57.2% discontinued their first course of hormonal therapy prior to course completion.  Of these patients, the top reasons for early discontinuation included progression of the disease (59.5%), adverse events (21.7%) and patient choice (10.1%).  Mean duration of therapy for all patients was 95.4 months (range 45.5–152.1). Time to discontinuation was significantly shorter for those who quit due to AEs than those who quit by choice (36.2 months vs. 57.8 months, p<0.0001). Of patients that discontinued due to AEs, hot flushes (46.1%), pain (19.1%) and nausea and vomiting (14.0%) were the most commonly reported events.  CONCLUSIONS: This analysis in a real world setting provides new insight into reasons for early discontinuation of hormonal therapy in the EU5.