Abstract Appreciation of the barriers and drivers affecting enrolment in RCTs is important for future trial design, communication and information provision. Although trials may address pertinent scientific questions, not all RCTs are equally attractive to patients. Many factors influence likely participation and include patients’ perceptions that novel treatments, or more treatment given for longer, must, in the context of life-threat, be better. Lack of awareness of such issues can lead to overly optimistic predictions of likely enrolment numbers and slow recruitment. Speedy completion of RCTs is required for drug approvals and timely introduction of efficacious therapies into clinics. We examined the barriers and drivers affecting recruitment to breast cancer trials in UK women. Method: As part of an intervention to facilitate effective multidisciplinary team communication about RCTs, patients who had discussed a trial with a doctor and/or research nurse completed study-specific questionnaires. Reasons for either accepting or declining trial entry were explored and patients indicated how strongly 16 separate statements had influenced their decision-making. Results: 152 women, median age 60, completed questionnaires about their reasons for participation or not in one of 16 different RCTs; 12 of these were chemoprevention, perioperative and adjuvant systemic or radiotherapy trials, 4 were for patients with advanced/metastatic disease. 113/152 (74%) patients consented to enrolment. Overall the primary reason 58/108 (54%) for trial acceptance was altruism- “I feel that others with my illness will benefit from the results of the trial”. Acceptors’ and decliners’ responses to 9/16 statements concerning decisions about trial participation differed significantly (p<0.02). In particular, ‘wanting to help with the doctor's research’ influenced 100% acceptors compared to 61% of decliners (p<0.001). Decliners were more likely to be ‘worried about randomisation’ (38% v 20%; p<0.016) and to ‘want the doctor to choose treatment rather than be randomised’ (49% v 30%; p<0.20). Irrespective of adjuvant or metastatic setting, trial design appeared to influence recruitment. Table 1: acceptance rates for different trial designsTrial designExampleAcceptanceperioperativePOETIC - 2 weeks perioperative endocrine therapy pre and post-surgery15/18 (83%)standard therapy versus standard + novel drugBETH - chemotherapy and trastuzumab +/- bevacizumab15/19 (79%)standard versus new therapy or regimenPERSPHONE - 12 versus 6 months trastuzumab43/57 (75%)placebo controlledREACT - double blind RCT celecoxib versus placebo29/42 (69%) Conclusion: A majority of respondents accepted RCT entry citing altruistic motivations as primary drivers for participation. Randomisation is a barrier and needs careful, reassuring justification. Trial design did seem to deter some, especially if one arm appeared to be offering less or no treatment. Explanations that longer treatment durations or regimens that include additional novel drugs may not necessarily enhance outcomes are especially important. Our findings may have implications for trial design, communication and the information provided during trial recruitment. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-11-03.