Abstract Introduction Patient-Reported Outcome Measures (PROM’s) are important tools that can enhance symptom management and patient quality of life in cancer treatment. Despite well-documented benefits, they are not often employed in routine care. This study aims to investigate the feasibility and acceptance of the integration of a dedicated mobile app for real-time symptom tracking and intervention using PROM’s among patients undergoing neoadjuvant or adjuvant chemotherapy for breast cancer. Methods We developed a dedicated mobile app for tracking PROM’s utilizing the NCI PRO-CTCAE to monitor 12 common chemotherapy-related symptoms. We aimed to evaluate patient acceptance and clinical feasibility of the app. Patient responses were directed to a personalized dashboard for designed for the clinical treatment team. We determined self-reported grade 3 or 4 vomiting, diarrhea, constipation, shortness of breath, cough, or peripheral neuropathy and grade 4 mucositis, nausea, or pain as symptoms severe enough to trigger an automatic alert requiring a phone call from our nursing staff for support. Each questionnaire generated up to 1 alert regardless of the number of severe symptoms. Symptomatic patients also received personalized automated instructions and video links for symptom management regardless of the severity of their symptoms. In response to staff feedback during the study, we added an additional assessment to determine whether patients with severe symptoms were interested in direct contact from the clinical staff when alerts were triggered. At baseline patients reported if they felt they were skillful at using smartphone apps. Quality of life, psychological and emotional health measures were collected at baseline, and weeks 6, 12, and 18. Categorical variable were described using percentages and compared using the chi squared test. Statistical analyses were performed by SPSS. Results: At the time of this analysis, 58 patients were recruited and found eligible for the study. All 58 patients self-reported as skilled with the use of smartphone apps. Eighteen patients (31%) withdrew from the study after receiving at least one questionnaire and their data was included up to their point of withdrawal. The different chemotherapy regimens given in the study are shown in table 1. Out of 772 questionnaires sent, 404 were returned, resulting in a 52% completion rate. These 404 completed questionnaires generated 126 (31%) alerts. After including feedback on the interest of direct contact from our nursing staff to manage alarming symptoms, only 23/102 (22.5%) alerts required clinical contact. Twenty-one patients (36%) did not complete even a single questionnaire. For the 37 (64%) patients who completed at least 1 questionnaire the completion rate was 74%. There was no significant difference in the alert rate of completed questionnaires between patients receiving TCHP, TC-AC-Pembro, and AC-T (38%, 38%, 29% p=NS). TC triggered significantly less alerts than AC-T (11% vs 29% p=0.01). Conclusion: The interim results of our ongoing study highlight the potential of a mobile app in real-time monitoring of chemotherapy-related symptoms. Our results suggest symptom monitoring using a dedicated mobile app is both acceptable and feasible for both patients and clinical personnel. The digital approach also seems effective in triggering alerts for severe symptoms, facilitating timely intervention. However, most alerts did not necessitate direct clinical contact, underscoring the role these interventions may play in allowing for patient self-care. However, over a third of patients did not utilize the app at all, emphasizing the need for further research examining the factors influencing the utilization of this technology for symptom monitoring. As the study continues, we hope to gain insights that can simplify and improve patient and clinician interaction with this tool, potentially improving symptom management for adjuvant breast cancer. Table 1 Chemotherapy Regimens DD AC-T dose dense doxorubicin cyclophosphamide paclitaxel, TCHP docetaxel carboplatin trastuzumab pertuzumab, TC-AC-Pembro paclitaxel carboplatin doxorubicin cyclophosphamide pembrolizumab, TC docetaxel cyclophosphamide,DD AC-T weekly dose dense doxorubicin cyclophosphamide paclitaxel weekly, TH paclitaxel trastuzumab, AC-THP doxorubicin cyclophosphamide paclitaxel trastuzumab pertuzumab, AC-TC doxorubicin cyclophosphamide paclitaxel carboplatin Citation Format: Opher Globus, Tal Sella, Amit Itay, Tali Shapira, Raisa Gold, Tami Modiano, Cecilia Oedegaard, Maya Krikli, Michal Bakalenik-Gavry, Beatrice Shaham, Alex Galper, Einav Nili-Gal Yam. An App-Based Approach to Monitor Chemotherapy Symptoms [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-13-01.