Abstract Accurate recruitment in performing clinical trials is crucial to avoid delays in the availability of potential beneficial treatments for patients. However, optimal strategies to improve it remain elusive and highly variable. The aim of this study was to identify the factors affecting recruitment from a multi-professional approach. Methods: A convergent mixed method study was used, including key informant in-depth interviews (n=13), 5 focus groups (n=40) and a 209-item Likert-scale survey for the measurement of a whole array of variables of interest (i.e. job attitudes, job satisfaction, job stressors and social status). A purposive sample of professionals from thirty-three clinical trial sites in Spain were targeted. Qualitative data were analyzed alongside quantitative data to document patterns and modifiers of recruitment performance. Audio material was recorded, transcribed verbatim and analyzed using the framework method. Findings: Pattern observed in qualitative data was confirmed in quantitative analysis. A total of 32 key barriers to successful patient recruitment were identified and clustered in three categories. The most commonly reported barriers and facilitators regarding a multifactorial approach were: System/organization: Counting on experienced recruiters and having a strong team-workforce awareness (92,3%); automated recruitment software, scientific culture, recruiting philosophy, adequate workload demands (88%); high stimuli and interprofessional trust (84%). However, lack of time devoted to clinical research in favor of assistance demands, excessive workload and bureaucratic tasks were the most salient stressors to fulfill professional research and recruitment responsibilities (54%). Working team conditions: Insufficient workforce support as well as high employee turnover contributed to emotional exhaustion and depersonalization and to a lower personal accomplishment (15%). Interpersonal relations affected not only motivation and performance but professionalism satisfaction with outcomes. Professional recruiter characteristics: Professionals with a high level of expertise and academic specialization (>5 years), greater active involvement in relevant clinical trials just as interprofessional prestige and recognition showed a greater satisfaction. Consequently, they were prompted to intensify their efforts to fulfill recruitment. The more effective clinical research settings were those better aligned with attributes for becoming high recruiters and with better multi-professional articulation. Suggestions to improve recruitment included providing professionals with devoted time for research, setting up collaborative research agreements, building a clinical research network, collaborative tumor registries, clinical trials data sharing resources, multidisciplinary functional units and committees, flexible staffing models and empowering oncologists/managers leadership. Conclusions: This study provided useful understanding of how to maximize patient recruitment at clinical research sites. Strong team-workforce and adequate workload were the most important identified factors for achieving it. Results will be used to inform professionals and stakeholders of the next steps needed and to engage them to fulfill accurate recruitment. Citation Format: Casas A, Gonzàlez X, Capelán M, Morales J, Fabián M, Ciruelos E, Gabriele G. Overcoming barriers to achieve a successful breast cancer patient recruitment: Professionals' views [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-13-05.