Abstract Background: Safe and effective use of two new treatments, T-DXd or olaparib, in breast cancer (BC) requires awareness, education and co-ownership by patients and care teams. It is hypothesized that a patient-centered digital app that provides disease and treatment-specific guidance and symptom reporting functionality while collecting specific data could positively impact patients’ confidence, self-monitoring of symptoms and experience of care. This study will develop and assess two new treatment-specific versions of the accredited OWise app to evaluate how BC patients accept and use the app and how use in routine care appears to impact patients and their experience of care in relation to monitoring symptoms. As a novel element, this study will explore the feasibility of combining treatment-specific real-world data collection with digital health support to understand how treatment patterns and characteristics in the real-world setting. OWise is a specific BC app that has been endorsed by NHS digital and is widely available through NHS app library in UK and in Netherlands. It currently has over 18K registered users. Trial Design: The study involves two workstreams which include several sources for data collection. Workstream 1 involves collection of participants OWise data (including patient entered data as well as usage statistics) and a brief survey for participants to provide feedback on their experience using OWise every three months for up to 18 months. Survey questions are focused on their perceptions of the usefulness of the app for monitoring their health changes and communicating with their care team. Workstream 2, will launch approximately three months after the launch of Workstream 1 and will include qualitative interviews with two groups of people: 1) a small number of participants who are already enrolled in Workstream 1 and 2) clinicians (and multidisciplinary team/nurses) to further understand the perceived benefits of the app. The study’s duration will be 21 months Eligibility Criteria: The patients must be prescribed either T-DXd or Olaparib and be at least 18 years of age, be able to create an OWise account (e.g., mobile or web application) and have activated the unique study code for the treatment specific version of OWise and be able to provide online consent for study participation Aims: Primary objectives are to evaluate the feasibility, acceptability, and perceived impacts on patient experience, treatment use, and quality of care of two treatment specific OWise apps in routine BC care. Secondary objectives will focus on prescribing patterns, concomitant medicine use in UK practice, understanding strategies used in the real-world setting to manage AE and demographic and clinical characteristics of patients treated in the UK Statistical methods: Aggregated Participant-level quantitative data and usage data will be analyzed for response frequencies, means, standard deviations (SD), medians, ranges, and confidence intervals (CI). Descriptive statistics and advanced statistics will be used to identify core variables and trends, investigate data distribution links between data, test significant differences between datasets according to profile/status. Target Accrual: 300 patients T-DXd and 150 olaparib using the OWise app and being part of the real-world study. The prescription decision is independent of the study enrolment. Contact: Dr Sophie McGrath. sophie.mcgrath@rmh.nhs.uk Citation Format: Sophie McGrath, Peter Hall, Michael Acquadro, Soren Skovlund, Parveen Jayia, Stuart McIntosh, David Cameron. RELATE 2: A real-world observational study assessing feasibility, acceptability, perceived impacts of digital apps for patients receiving olaparib or trastuzumab deruxtecan (T-DXd) as part of routine clinical practice [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 PO4-17-07.