Objectives <p>Despite significant potential adverse health outcomes, many cancer survivors continue smoking. Few smoking cessation interventions have demonstrated efficacy above standard treatment for this population. Through a rigorous iterative process, we developed a prototype smartphone app that addresses both general and cancer-specific relapse risks in real time, incorporating cancer survivors’ feedback. We report findings from two studies: (1) Qualitative interviews and brief surveys to inform intervention development and (2) Usability testing of the prototype app in a 4-week single-arm pilot trial.</p> Method <p>Cancer survivors (Study 1: <i>n</i> = 20; Study 2: <i>n</i> = 12) who had smoked at least one cigarette within the past 30&#xa0;days were enrolled. Study 1 participants completed a 50-minutes Zoom interview and survey to inform intervention content and the app design. Subsequently, a prototype app was developed and tested for usability in Study 2, which included ecological momentary interventions (EMIs), three telehealth counseling sessions, and nicotine patches. Baseline and end-of-treatment (EOT) surveys and interviews were completed.</p> Results <p>Key findings in Study 1 included high perceived helpfulness of mindfulness and EMIs for managing cravings and cancer-related stress, and a reported strong willingness to use the app. In Study 2, eleven participants used the app and completed counseling sessions. Participants reported high treatment acceptability, app usability, and ease of use. A key suggested improvement was adjusting the timing of app notifications.</p> Conclusions <p>Results support continued investigation of this app. Next steps include testing the feasibility and acceptability of the app for smoking cessation.</p> Preregistration <p>Study 2 is registered in ClinicalTrials.gov (NCT06476548).</p>