Background: Disease Pathway Management (DPM) is used by Cancer Care Ontario (CCO) to set priorities for cancer control, plan cancer services, and improve the quality of care in Ontario by promoting standardization. The DPM approach applies a framework to examine the performance of the entire system from prevention to end of life care, and to identify any gaps within the system. In 2014, DPM began its breast cancer pathway initiative by mapping the patient journey, depicting evidence-based best practice along the breast cancer care continuum, identifying where further guidance is needed for clinical decision making, and identifying gaps in quality of care and performance measurement indicators. Objective: To evaluate the impact of DPM on quality assessment of breast cancer care in Ontario. Methods: DPM convened a multidisciplinary breast cancer working group (WG) of 40 experts from across Ontario. The WG held 12 meetings and used guidelines developed by CCO’s Program in Evidence Based Care (or other sources as needed) to generate pathways for the prevention, screening and diagnosis, treatment, and follow-up care for breast cancer. The pathways were used as a framework to review the existing inventory of provincial breast cancer quality indicators, and to identify areas where evidence based guidance is needed. The pathways were subjected to an extensive review process before publication. Results: The expert WG identified 28 priority areas, including opportunities to develop guidance in areas where it is lacking (e.g. role of perioperative breast MRI; indications for contralateral prophylactic mastectomy) and system barriers that may hinder optimal care (e.g. biomarker assessment). The WG also used the pathways as a framework for evaluating performance measurement indicators by mapping 48 existing quality indicators for breast cancer to the pathway. Conclusions: The CCO DPM Breast Cancer pathways facilitated a province-wide, multidisciplinary process to promote quality standards, to identify gaps and overlaps in performance and quality measurement, and to recommend additional indicators more relevant to the quality of breast cancer care in Ontario.