Abstract Background The lifetime risk of developing breast cancer is 1 in 8 for women in the Netherlands. Breast cancer care in the Netherlands is of high quality, resulting in low 5-year local recurrence rates of 1.5% after breast conserving therapy and 2.7% after mastectomy. Although good endpoints of breast cancer treatment are obtained, it is expected that further improvement of care can be achieved since unexplained variation in a number of treatment aspects was found between hospitals in the Netherlands. Clinical audits provide an important tool for quality assessment. Worldwide, only a few nationwide clinical audits for breast cancer care are currently running. In the Netherlands, a nationwide multidisciplinary clinical audit started three years ago. Material and methods The multidisciplinary national NABON Breast Cancer Audit (NBCA) started collecting data of all Dutch hospitals in 2011, facilitated by Comprehensive Cancer Centre the Netherlands (IKNL) and Dutch Institute for Clinical Auditing (DICA). The NBCA has several purposes: nation-wide evaluation of quality parameters, evaluation of guideline adherence, and providing weekly updated feedback to participating institutions. Results All Dutch hospitals (n=92) participate by providing data regarding delivered breast cancer care resulting in a database of more than 42.000 breast cancer patients (5.745 DCIS and 36.396 invasive carcinomas) in three years time. Eighty-nine percent of invasive breast cancer patients were treated with primary surgery of which 62% (n=19.885) with breast conserving surgery. Within three years time, several quality assessments improved such as guideline compliance for pre- and postoperative multidisciplinary team meetings, percentage of patients starting surgery within five weeks (see table). The percentage of patients that were treated with preoperative systemic treatment (12%; 95% CI: 0 – 47%) and patients receiving an immediate reconstruction after ablative surgery (19%; 95% CI 0 – 73%) still remained low with a large variation between hospitals. At the conference, results will be substantiated by funnelplots. Other quality indicators will be presented as well. Table 1. Quality indicator results and their improvement over years.20112013Preoperative MDT81%96%Postoperative MDT90%98%Time to operation ≤5 weeks (immediate reconstruction after mastectomy excluded)80%85%Tumor positive margins invasive breast cancer (without PST)6.1%5.0%Tumor positive margins DCIS25%20%PST for invasive breast cancer10%12%Immediate reconstruction after ablative surgery for invasive breast cancer15%19%Immediate reconstruction after ablative surgery for DCIS39%44%MDT= Multi-disciplinary team meeting; PST= Primary Systemic Treatment; DCIS= Ductal Carcinoma In Situ Conclusions The continuous cycle of registration and providing feedback by clinical auditing provides a powerful tool for quality monitoring and improving breast cancer care. Improvements of monodisciplinairy surgical and pathological aspects of care have been reached in a relatively short time period. However, for more complicated multidisciplinary issues like the use of primary systemic treatment and immediate reconstruction, detailed analyses of the variation between hospitals is needed to further improve these aspects of breast cancer care. Citation Format: Annelotte C van Bommel, Marie-Jeanne T Baas-Vrancken Peeters, Margriet van der Heiden - van der Loo, Thijs van Dalen, Emiel J Rutgers, Michel W Wouters, Marc B Lobbes, Ruud M Pijnappel, Marc A Mureau, Pieter J Westenend, Bart de Vries, Carolien H Smorenburg, Agnes Jager, John H Maduro, Henk Struikmans, Carol Richel, Marga Schrieks, Maike Schepens, Sabine Siesling, Vivianne C Tjan-Heijnen. The NABON breast cancer audit; quality improvement in three years' time [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-07-18.