BACKGROUND: Worldwide, many clinical trials are performed using clinical outcomes and surrogate outcomes as endpoints. Surrogate outcomes are used, for instance, if there is not enough follow-up time to measure the outcome of interest. Surrogate outcomes might not be patient-relevant, however. This study assesses to what extent patient-relevant outcomes are measured in clinical trials for breast cancer drugs. RESEARCH DESIGN AND METHODS: A cross-sectional comparative analysis was conducted in which patient preferences for outcomes derived from the literature were compared to outcomes measured in phase III breast cancer trials conducted between 2014 and 2024. RESULTS: Patients prefer outcomes addressing survival benefits, treatment effectiveness, adverse events and health-related quality of life. Minor improvements in survival benefits are greatly valued. The majority of patients are willing to accept some side effects for a positive outcome. The primary outcome used most frequently in trials is progression-free survival. The most common secondary outcomes are adverse events, mortality, overall response rate and health-related quality of life. CONCLUSION: Phase III trial outcomes appear to align largely with breast cancer patients' preferences. Nevertheless, patients and trial designers emphasize different outcomes. Improvement is therefore needed to enhance the relevance of trial data for patients.