This paper describes a project employing decision-centered design to develop a decision support application called the Screening & Surveillance App (SSA) to aid primary care providers in tracking and managing colorectal cancer (CRC) screening for their patients. This paper details the path from cognitive task analysis (CTA) to a decision support application. We conducted ethnographic observations and CTA interviews to identify common elements of clinical workflow across health systems and articulate decision requirements. We describe three design iterations that emerged over the course of CTA and software development. Findings from a beta test evaluating the SSA suggest that it saves time, increases accuracy in responding to CRC-related patient-specific questions, and is perceived to reduce workflow as compared to participants' current electronic health records (EHR). Usability and usefulness ratings for the SSA as measured by the Health ITUES were above 4 on a 5-point scale where 5 was most positive.