Background: Fear of cancer recurrence (FCR) is prevalent, persistent and a common unmet need. Patients indicate desire to discuss FCR with their oncologists, however most clinicians are not trained to manage FCR. Our team developed a novel clinician-driven educational intervention to help patients manage FCR (the Clinician Intervention to Reduce Fear of Recurrence (CIFeR) intervention). In earlier work, we demonstrated the feasibility, acceptability, and efficacy of CIFeR in reducing FCR in breast cancer patients.¹ This study aimed to explore the barriers and facilitators to implementing this low-cost brief intervention within routine oncology practice. Methods: This multicentre, single-arm Phase I/II implementation study recruited medical/radiation oncologists and surgeons who treat women with early-stage breast cancer. Participants completed online CIFeR training on importance of doctor-lead discussions and 5 steps on how to discuss FCR with video demonstration. Participants then incorporated CIFeR in consultations with suitable patients for the next 6 months. Questionnaires were administered at baseline (T1), immediately post-training (T2), then 3 month (T3) and 6 month (T4) after training to assess confidence addressing FCR and implementation outcomes. The primary outcome of CIFeR_2 was adoption (percentage of clinicians who offer CIFeR to at least one patient in routine practice within 3-months after training). Secondary outcomes were clinician self-efficacy in FCR management, perceived acceptability, feasibility, costs, barriers and facilitators of implementation. Results: 52 clinicians (30 medical oncologists, 13 radiation oncologists and 9 surgeons) consented to the study, of whom 35 completed CIFeR training and T2 questionnaires and 28/31 completed T3 and 20/24 completed T4 questionnaires. Mean age was 43±8.6, 75% were female. CIFeR was adopted by 86% of participants, and was utilised on average 4 (range 0-10) times by trained clinicians by T3. Participants reported CIFeR taking on average 7 minutes (range 2-15min) to deliver. CIFeR was deemed acceptable, appropriate and feasibile by participants at T3. Self-efficacy in managing FCR improved significantly across all domains from T1 to T2 (n = 35, p < 0.001). Perceived difficulty with managing FCR decreased from 2.5 to 2.1 (p = 0.009) from T1-T3. Lack of time was the greatest barrier to CIFeR_2 implementation. Conclusions: A structured brief, low-cost clinician intervention to reduce FCR is useful, acceptable and improved self-efficacy with FCR management in clinicians. FCR training should be incorporated in communication skills training of oncologists and surgeons. CIFeR is currently being adapted to address fear of progression in patients with advanced cancer. Liu J, et al (2021) JCO Oncology Practice 17(6):e774-784. Clinical trial information: ACTRN12621001697875.