An interactive activity designed for use on an iPhone, this program estimates the risk of recurrence I gastrointestinal stromal tumor (GIST)—a GI cancer—using various assessment methodologies. The application features 4 representative GIST patients and allows you to select input for key tumor-related prognostic factors. The recurrence risk is then calculated utilizing 3 of the leading risk assessment tools, which were developed in conjunction with government institutes and major cancer organizations. It is intended as an educational exercise for use by oncologists and other healthcare professionals who are involved in the evaluation of patients after resection of a primary GIST. This easy-to-use application underscores not only the importance of assessing the risk of recurrence, but also how the estimated risk is influenced by tumor factors such as size, site, and mitotic rate, as well as the selected assessment approach. Clinicians are encouraged to use this application to further their understanding of risk stratification in GIST to enhance their clinical decision making.