Abstract Purpose: Hospitals face many challenges in effective care coordination for post-surgery breast cancer patients, especially with scarce resources and limited availability of nurse navigators for care transition and post-hospitalization follow up. Mobile health provides an inexpensive and convenient means of real time care monitoring and communication between patients and care providers. Nevertheless, most current health apps focus on individual consumers and gather information from their daily lives, but do not integrate with clinical workflow or capture physiological and activity data into electronic medical record for real-time monitoring, patient surveillance, and professional care. To fill this gap, we have developed and implemented MOCHA (MethOdist Hospital Cancer Health Application), a coordinated care mobile app for post-hospitalization breast cancer patients from the perspective of a primary care institution. Methods: MOCHA supports both iOS and Android platforms and contains two main modules: health care monitoring and data communication, designed together with the physicians and nurses of the Houston Methodist Cancer Center. The Health care monitoring module aims to support real-time monitoring of the post-discharge medical state of breast cancer patients. Physicians can monitor the daily food intake and activities for patients and provide advice to patients in real-time. The data communication module was developed to safely exchange the care coordination data with the hospital electronic medical record or data warehouse. Communication between the patient and the physician can be via an in-house protocol or an open data exchange standard Fast Healthcare Interoperability Resources (FHIR), that describes data format and elements for exchanging electronic health records. Our communication module uses https-based protocol to exchange the structured data with the FHIR resource server. Implementation: To validate the MOCHA app, we collaborated with the oncologists and dietitians at the Houston Methodist Cancer Center, who provided breast cancer patients for post-surgery care coordination. Our app exchanges health care data in real time with our hospital's clinical data warehouse. MOCHA searches Nutritionix food database for nutritional information and uses personal trackers such as Fitbit for patients' daily activities with their authorization. The app sends patients' daily burned calories into our clinical data warehouse. During the evaluation period, the physician communicates with cancer patients daily. In addition, every patient has a bi-weekly physical examination, and all examination results are shown in the app. After the experimental evaluation, the physician will access the data warehouse and analyze the test data in order to improve the quality of care coordination. The experimental clinical evaluation is ongoing, and we will report the results once the study is completed. Conclusion: MOCHA app provides health care monitoring and secure communication functions with interface with clinical data warehouse. The technical evaluation shows that the proposed methods are robust and efficient in support of care coordination for post-surgery cancer patients. Citation Format: He T, Ogunti R, Yu X, Puppala M, Chen S, Mancuso J, Stephen W. MOCHA: An institution-based care coordination app for post-hospitalization breast cancer patients [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 P5-11-12.