Advances in treatment have fortunately led to a growth in the number of childhood cancer survivors in the US. Unfortunately, these survivors are at-risk for negative late effects from treatment, including cardiovascular disease and early death. Physical inactivity can exacerbate these risks. Adolescent survivors of childhood cancers in particular have reported significant declines in physical activity that persist following treatment Katie Devine Recuay, PhD, seeks this career development award to become an independent investigator in pediatric cancer survivorship, specializing in the concerns of adolescent and young adult (AYA) survivors. Her long-term goals are to promote healthy behaviors and enhance quality of life for AYA survivors of childhood cancers. Short-term goals include specialized training in: (1) the use of mobile health "mHealth" technology for implementing behavioral interventions, (2) biological and clinical aspects of AYA cancer survivorship, (3) the conduct of multi-site randomized clinical trials (RCTs) using behavioral interventions, and (4) exercise physiology and methods of assessment. Along with her mentors and advisory team, she has developed a training plan with specific activities to reach these goals through a combination of formal coursework, seminars, hands-on training in the assessment of cardiovascular and physical fitness, and a research project mentored by a multidisciplinary team of experts in cancer control, behavioral sciences, and exercise science. The proposed research project involves the creation of a cancer-specific mobile application (app) that complements a group-based weekly fitness program, and pilot testing of the effectiveness of this technology- enhanced program. The app will be developed based on input from AYA survivors and preliminary work she has done in this area. In the pilot RCT, 88 AYA survivors will be randomized to either the technology-enhanced fitness program or waitlist control. The primary outcome is objectively measured cardiovascular fitness. Secondary outcomes include muscle strength, health-related quality of life, and fatigue. We hypothesize that participants in the intervention group will demonstrate greater improvement across primary and secondary outcomes compared with the waitlist control. This project is innovative in its use of mHealth technology and the specificity of the intervention to AYA survivors of childhood cancers. The proposed career development plan will facilitate Dr. Devine's transition to an independent investigator with expertise in AYA survivorship concerns and the use of mHealth technology in behavioral interventions.