BACKGROUND: We aimed to identify demographic and health-related predictors of declining physical activity levels over a four-year period among participants in the Childhood Cancer Survivor Study. METHODS: Analyses included 7,287 ≥5-year childhood cancer survivors and 2,107 siblings who completed multiple follow-up questionnaires. Participants were classified as active if they met the Centers for Disease Control and Prevention guidelines for physical activity. Generalized linear models were used to compare participants whose physical activity levels declined from active to inactive over the study to those who remained active. In addition, selected chronic conditions (CTCAE v4.03 Grade 3 and 4) were evaluated as risk factors in an analysis limited to survivors only. RESULTS: The median age at last follow-up among survivors and siblings was 36 (range, 21-58) and 38 (range, 21-62) years, respectively. The rate of decline did not accelerate over time among survivors when compared with siblings. Factors that predicted declining activity included body mass index ≥30 kg/m(2) [RR = 1.32; 95% confidence interval (CI), 1.19-1.46, P \u3c 0.01], not completing high school (RR = 1.31; 95% CI, 1.08-1.60, P \u3c 0.01), and female sex (RR = 1.33; 95% CI, 1.22-1.44, P \u3c 0.01). Declining physical activity levels were associated with the presence of chronic musculoskeletal conditions (P = 0.034), but not with the presence of cardiac (P = 0.10), respiratory (P = 0.92), or neurologic conditions (P = 0.21). CONCLUSIONS: Interventions designed to maximize physical activity should target female, obese, and less educated survivors. Survivors with chronic musculoskeletal conditions should be monitored, counseled, and/or referred for physical therapy. IMPACT: Clinicians should be aware of low activity levels among subpopulations of childhood cancer survivors, which may heighten their risk for chronic illness
