Abstract Background: Breast cancer exhibits significant molecular, pathological, and clinical heterogeneity. Current clinicopathological evaluation is imperfect for predicting outcome, which results in overtreatment for many patients, and for others, leads to death from recurrent disease. Therefore, additional criteria are needed to better personalize care and maximize treatment effectiveness and survival. To address these challenges, large-scale population-based studies are needed to develop and evaluate new predictive biomarker tests under real-world conditions. Methods: In 2010 we initiated the Sweden Cancerome Analysis Network - Breast (SCAN-B) multicenter prospective study (ClinicalTrials.gov identifier NCT02306096) with longsighted aims to 1) analyze breast cancers with next-generation genomic technologies for translational research in a population-based manner and integrated with healthcare; 2) decipher fundamental tumor biology from these analyses; 3) utilize genomic data to develop and validate new clinically-actionable biomarker assays; and 4) establish real-time clinical implementation of molecular diagnostic and treatment-predictive tests. Eligibility criteria are suspicion or confirmed diagnosis of primary breast cancer. Eligibility will be extended to recurrent breast cancer in late 2016. For all patients, tumor biopsy and/or surgical tumor specimen and baseline blood samples are collected, as well as follow-up blood samples at defined intervals, and clinical data are obtained from regional and national databases. From all samples, DNA, RNA, and protein fractions are isolated, and tissue arrays are constructed. In the first phase, we focus on molecular profiling of tumor tissue by next-generation RNA-sequencing. Results: From August 2010 through May 2016, we have consented and enrolled 8,669 patients with primary breast cancer at 9 hospital sites in Sweden, representing approximately 85% of eligible patients in the catchment area. Preoperative blood samples have been collected for 8,288 (96%) patients and primary fresh-frozen tumor specimens collected for 6,129 (71%) patients. All tumors have been RNA-sequenced, and newly enrolled cases are analyzed in “real-time” within an average of 7 days after biopsy/surgery. Herein we describe the study infrastructure and protocols and present initial proof of concept results from prospective RNA-sequencing including tumor molecular subtyping, detection of driver gene mutations, and determination of ER, PgR, HER2, Ki67, and tumor grade from RNA-seq data. Prospective patient enrollment is ongoing and pilot clinical reports are being evaluated at multidisciplinary breast cancer conferences. Conclusions: We demonstrate that population-based collection and real-time RNA-sequencing analysis of breast cancer is feasible at large-scale. The SCAN-B Study should significantly reduce the time to discovery, validation, and clinical implementation of novel molecular diagnostic and predictive tests. We welcome the participation of additional comprehensive cancer treatment centers. Citation Format: Saal LH, Hegardt C, Vallon-Christersson J, Häkkinen J, Ehinger A, Manjer J, Larsson C, Loman N, Rydén L, Malmberg M, Borg Å. The SCAN-B study: 5-year summary of a large-scale population-based prospective breast cancer translational genomics platform covering a wide geography of Sweden (NCT02306096) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-07-17.