ABSTRACT Latinx childhood cancer survivors have an increased risk of cardiometabolic dysfunction. While physical activity (PA) is associated with lower risk of cancer recurrence, cardiometabolic dysfunction, and higher quality of life, 57% of Latinx survivors are inactive. Culturally tailored interventions to increase PA for Latinx AYA survivors do not currently exist despite their urgent need. We will address this critical gap by efficiently leveraging the infrastructure in the Children’s Oncology Group (COG) created by our ongoing StepByStep randomized controlled trial (RCT; U01CA246665) that investigates a mHealth PA intervention in AYA childhood cancer survivors among English-speakers. Despite the COVID-19 pandemic, we have been successful in enrolling patients from COG, conducting assessments and intervention components remotely. Because the U01 StepByStep RCT is limited to English speakers, we propose (1) to apply a cultural centering process for behavioral interventions, using the general StepByStep intervention as a starting point, to create a novel intervention and (2) to test the resulting culturally tailored intervention in a short term efficacy RCT. We will efficiently extend our established study infrastructure within COG to recruit Latinx survivors who speak Spanish and/or English. In response to PAR-21-190 (Modular R01), we propose the following Specific Aims: 1. Use an iterative approach to develop a novel, culturally tailored multilevel remote-based physical activity intervention among 20 Latinx AYA childhood cancer survivors whose preferred language is Spanish or English. The iterative process will combine 3 rounds of testing of the intervention components alternating with qualitative interviews to obtain participant feedback to guide intervention modifications. 2. Conduct a RCT to test the novel culturally tailored remote-based physical activity intervention to demonstrate efficacy over 12 weeks among a separate group of 160 Latinx AYA childhood cancer survivors whose preferred language is Spanish or English (n=80 per randomization arm) and who do not meet PA guidelines. The control group will receive a Fitbit only. We will test the following hypotheses (H): H1: Intervention participants will have greater increases in moderate-to-vigorous PA (primary outcome) than controls as assessed by accelerometry. H2. Intervention participants will have greater improvements in cardiopulmonary fitness and resting heart rate than controls as assessed by the 2-minute step test and heart rate monitor (exploratory outcomes). H3: Intervention participants will have greater improvements in global, physical, and social functioning and fatigue than control patients as assessed by validated self-report instruments (exploratory outcomes). 3. Conduct two rounds of post-trial qualitative interviews, n=30 for the intensive intervention phase and n=30 for the maintenance intervention phase, to determine acceptability of and guidance on improving both intervention phases in preparation for a fully powered, longer term RCT.

PROJECT NARRATIVE Most Latinx childhood cancer survivors do not attain recommended amounts of physical activity and are generally sedentary, which increases their risk of chronic health conditions. This project in adolescent and young adult Latinx childhood cancer survivors whose preferred language is Spanish or English will culturally tailor and the test the efficacy of a new physical activity intervention consisting of a physical activity tracker integrated with individualized goal setting and a private social media group to improve physical activity, cardiovascular health, and quality of life. If efficacious, this portable and scalable intervention will fill a critical gap to reduce complications from cancer treatment among Latinx survivors.