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Background: POSNOC is a UK-ANZ multicentre, non-inferiority, randomised trial comparing systemic therapy alone with systemic therapy plus Axillary Treatment (Axillary radiotherapy or ALND) for women with ≤2 macrometastases at SNB. The primary outcome is axillary recurrence within 5 years. This paper describes screening, recruitment and compliance data. Methods: Sites were requested on a monthly basis to upload screening data and provide reasons for non-recruitment of eligible patients into the trial. Sites entered in the online database whether the patients were compliant with their randomisation allocation. Results: The study opened in July 2014 and completed target recruitment of 1900 women (24% of those screened) in July 2021, at 95 sites in the UK and 20 sites in Australia and New Zealand. The reason for non-enrolment was unknown in 1300 women. Of the remaining 4774 women with known reasons, who were screened but not randomised, the most common reasons for non-recruitment were due to either patients (n=2219, 46.5%) or their clinicians (n=782, 16.4%) favouring axillary treatment, or patients (n=490, 10.3%) or their clinicians (n=170, 3.6%) not wishing to have axillary treatment. Over the course of the study, there was an increase in the proportion of patients wanting axillary treatment and declining the trial (Mean % patients declined 2015 – 17.9%, 2021 – 39.1%). Mean number of participants recruited per site per month was 0.24 (SD 0.18) overall, 0.25 (SD 0.19) in the UK, and 0.19(SD 0.15) in ANZ. The mean was < 0.3 in 79 sites and >0.9 in only one site. Recruitment rate remained consistent throughout the study (mean 25.3 per month) except for during the first 6 months of recruitment (5.7) and during the COVID pandemic Apr-Sep 2020 (7.5). Of 89 (4.8%) participants non-compliant with allocation, n=45 (50.6%) received systemic therapy alone and n=44 (49.4%) received systemic therapy plus axillary treatment. There was no fluctuation in the direction of non-compliance during the study duration. There was increasing uptake of axillary radiotherapy to treat the axilla instead of ALND over the course of the study in patients receiving axillary treatment (Number who had ART of all who had axilla treatment2014-2017 - 248/454 (54.6 %); 2018-2021 – 315/449 (70.2%)). Conclusion: Recruitment and compliance with randomised allocation remained consistent over a seven-year period. POSNOC with in-built radiotherapy QA will provide definitive data on axillary management in patients undergoing mastectomy or BCS with ≤2 macrometastases on SNB. Citation Format: Amit Goyal, Cydney Bruce, Shabina Sadiq, Mickey Lewis, Alan Montgomery, G Bruce Mann, Heath Badger, Kathryn Monson, Valerie Jenkins, Lesley Fallowfield, Malcolm Reed, David Dodwell, Patricia Fairbrother, Tara Homer, Luke Vale, Roeum Butt, Elizabeth Miles, Shelley Dowey, Lucy Matthews, Hugh Jarrett, Juliet Jackson, Arfan Ali. Recruitment, clinical equipoise, patient acceptance and compliance in the UK-ANZ POSNOC trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-01-07.