RecruitingBehavioural interventionUsing Tailored mHealth Strategies to Promote Weight Management Among Adolescent and Young Adult Cancer SurvivorsThe AYA WELL study is a 2-arm randomized clinical trial to test the efficacy of a theory-based, mHealth weight management intervention adapted specifically for adolescent and young adult cancer survivors compared to a self-guided arm. Participants, diagnosed with cancer between ages 15-39, currently age 18-39, post-treatment at least 6 months, and who have overweight or obesity will be randomized to receive either: 1) a comprehensive mHealth weight management program (intervention) or 2) digital tools + health education + peer support (self-guided) over 12 months. Outcomes will be assessed at 3, 6, and 12 months.