Patients' daily reporting of symptoms via mobile application reveals a significant difference between patients' perceptions and doctors' interpretations.

Purpose: Electronic patient-reported outcomes (ePROs) are gaining importance. The aim of this study was to investigate the difference in the reporting of symptoms between patients via mobile application (m-app) and doctor assessments. Additionally, usability and satisfaction with the use of the m-app were assessed. Methods: In this single-center prospective cohort study, we analyzed ePROs in 46 patients receiving (neo)adjuvant chemotherapy for early breast cancer. Patients recorded the occurrence and intensity of symptoms via the Android-based m-app daily. Three-monthly, patients completed validated quality of life questionnaires (EORTC C30 and BR23). For the 10 most common symptoms reported by patients, we compared the frequencies and grades between patients and doctors. Additionally, we compared daily symptom reports with questionnaire results. Finally, the usefulness of and level of satisfaction with the m-app by patients and doctors were evaluated. Results: During the study, patients recorded almost twice as many different symptoms through the m-app as doctors did in the electronic health records (75 Conclusion: This study revealed a significant discrepancy between patients' daily symptom reports via the m-app and doctors' assessments, indicating that healthcare professionals may not fully capture patients' experiences. This underscores the importance of integrating PROs to accurately evaluate patients' conditions. Our m-app serves as a promising tool for reporting and managing side effects during systemic treatment of breast cancer.