PURPOSE: This study aimed to identify preferences of patients with high-risk hormone receptor positive/human epidermal growth factor receptor 2 negative (HR + /HER2-) early breast cancer (EBC) related to adjuvant endocrine therapy (ET) using the Adaptive Choice-Based Conjoint (ACBC) method. METHODS: A stepwise multimodal study was conducted in Germany between October 2021 and March 2022 consisting of desk research, qualitative interviews, and quantitative online surveys. Included patients had a high risk of recurrence at the time of their HR + /HER2- EBC diagnosis, completed primary therapy (surgery ± radiation + (neo)adjuvant chemotherapy), and were prescribed or undertaking adjuvant ET. In the desk research phase, online resources, patient material, and existing studies were reviewed. In the qualitative phase, interviews were conducted with 6 gynaecologists, 6 oncologists, 20 patients, and 5 caretakers. In the quantitative phase, 85 patients completed the ACBC analysis survey. RESULTS: Included patients were aged 49.4 years (mean) among which 69.4% were still working. In the ACBC absolute rating, diarrhoea, arthralgia, and nausea were least relevant attributes to patients. Relative assessment of ET attributes against each other revealed that achieving the ET goal, namely the reduction of risk of tumour recurrence, had the highest relevance, while avoiding side effects and maintaining quality of life were less relevant. Overall, 35% have considered taking a break or discontinuing adjuvant ET due to side effects. CONCLUSION: Reduction of tumour recurrence was the attribute of highest relative importance for patients with high-risk HR + /HER2- EBC followed by side effect avoidance and quality-of-life maintenance, reflecting their importance in treatment decisions.