Background: Nonadherence to prescribed medications occurs frequently in patient with breast cancer (BC) and can affect BC outcomes as well as outcomes for comorbid conditions. We implemented a process to screen for medication adherence in the electronic health record (EHR) in an urban outpatient BC clinic. Methods: Plan-Do-Study-Act (PDSA) methodology was used to implement a screening process for medication adherence for all patients seen in the outpatient breast oncology clinic. At check-in (via the patient portal or clinic based kiosks), patients were asked to complete an EHR adherence screener. Two PDSA cycles were completed. During cycle one (2/16/22-5/17/22), patients were asked if they received ≥1 prescribed medication; if yes they were asked to complete the questionnaire (y/n); if yes a 3-item questionnaire was used to screen for adherence to all medications over the prior 7 days. Adherence was defined as 3 of 3 responses “none of the time” to “I have missed my medicine;”“I have skipped a dose of my medicine;” and “I did not take a dose of my medicine.” During cycle two (5/17/22-6/5/22) the screener was simplified. Patients were no longer asked to complete the survey; and the survey was modified to 1-item “I did not take a dose of my medicine”, adherence was defined as response of “none of the time”. We evaluated response rate and self-reported non-adherence rate. Results: During PDSA cycle 1 (2/16/22-5/17/22), 2840 visits occurred and 722 (25%) responses were received; 80% noted prescription of ≥1 medication, 38% agreed to complete the survey; and 87% reported adherence to all prescribed medications while 13% reported non-adherence. During PDSA cycle 2 (5/17/22-6/5/22), 512 visits occurred and 172 (33%) responses were received. Of those, 73% reported prescription of ≥1 medication; of those 66%-reported adherence to all prescribed medications, 21% reported non-adherence, and 17% preferred not to answer. Conclusions: This EHR screener is a simple and scalable tool to rapidly screen for medication adherence. Up to a quarter of patients who completed screening reported non-adherence. Further tools are needed to assess adherence among patients who lack access to the patient portal or clinic kiosk, or are uncomfortable checking in with these mechanisms. Future interventions are necessary to further screen potentially non-adherent patients and for interventions to improve adherence once vulnerable patients are identified.