Background: Most patients diagnosed with breast cancer will have early stage (stage I or II) disease, with low chance of distant metastases. Thus most guidelines, including Choosing Wisely, recommend against imaging tests for distant metastases in asymptomatic early stage breast cancer. Despite this, most (86%) of these patients in Ontario received these tests from which they are not likely to benefit and may result in investigations that can be invasive and delay treatment. Publicly reported indicators, such as those in Ontario’s Cancer System Quality Index (CSQI), can bring research findings to action by identifying areas for improvement and facilitating ongoing assessment. In practice, this can be challenging due to limitations in administrative data. Moreover, relatively few quality improvement indicators focus on efficiency, the dimension of quality looking at best use of resources to achieve desired outcomes. We sought to examine trends in the use of imaging tests in early stage breast cancer and to drive quality improvement efforts via public reporting. Methods: Data from the Ontario Cancer Registry, the Discharge Abstract Database and the Ontario Health Insurance database was used to identify how many Ontario breast cancer patients diagnosed with early stage breast cancer received staging tests from 2012–2014. Imaging tests included were ultrasound, CT scan, MRI, x-ray and bone scan. The results were subsequently shared with the Regional Cancer Centres and publically released in the CSQI. Results: From 2012 to 2014, 75.1, 72.7 and 71.3% respectively of early stage breast cancer patients received at least one imaging test for staging. This is much higher than the 5-10% of patients expected to need tests due to symptoms or comorbidities. While the regional variation ranged from 47-80%, the rates were high across the province with no clear pattern. Conclusions: Public reporting may be having some effect on overtesting, but rates remain high. Following outreach by the Cancer Quality Council of Ontario and Cancer Care Ontario, targeted regional interventions are being developed and implemented, the impact of which will be assessed and reported in future releases of the CSQI.