Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Osteosarcoma (OS) is the most common form of bone cancer in children and displays a peak incidence that coincides with the pubertal growth spurt. Consequently a number of studies have investigated whether cases are taller at diagnosis than the general pediatric population; a recent analysis which pooled seven such studies found that cases were disproportionately in the 51st-89th and especially the >90th percentiles of height-for-age (HFA). However, no study to our knowledge has examined whether OS patients exhibit greater HFA at earlier ages. During 2008-2010 we enrolled 290 OS cases <20 years of age diagnosed at Children's Oncology Group institutions in the United States and Canada in a genetic epidemiologic study. In addition to collecting buccal cell samples for genetic analysis we requested permission to obtain length/height data from medical records from birth to diagnosis. Records were obtained for 153 male and 111 female participants. Anthropometrics and date of measurement were doubly entered into a custom database, and inconsistencies were resolved by a third abstraction. Between 1 and 46 measurements (median = 11) were recorded up to the earlier of diagnosis or 12 years of age. Mixed effects cubic spline models were applied to length/height to produce individual growth curves using Stata. Sex was included as a main effect and as interactions with the model slope terms to account for gender differences in growth. Individual estimates of length/height at every three months of age between birth and age two years, and at each year of age thereafter, were computed and transformed to Z-scores according to the CDC 2000 reference. OS cases of both sexes were consistently longer or taller than reference data at all ages, as at no age did the 95% confidence interval around mean Z-score include 0 (i.e. the population mean and median). Under 2 years of age length was examined; mean Z-score at birth was 0.56 (71st %ile), rose to 0.72 (76th %ile) at 0.5 years, and fell to 0.31 (62nd %ile) at 2 years. Over 2 years of age height was examined; mean Z-score was 0.48 (68th %ile) at 4 years, dipped to 0.33 (63rd %ile) at 8-9 years, and rose to 0.49 (69th %ile) at 12 years. No differences in mean Z-score at each age were observed by age at diagnosis (sex specific inter-quartile range of age at diagnosis vs. other), location of tumor (long bone of the lower limb vs. other), or race (White non-Hispanic vs. other). Our data clearly indicate that pediatric OS patients are substantially longer/taller than the United States national norm at all ages before puberty. Citation Format: Logan G. Spector, Kathryn Ritter, Ellen W. Demerath, Charles Sklar, Julie A. Ross, Mark Krailo, Rajaram Nagarajan, David Malkin, Tracy L. Bergemann, Sharon A. Savage, William Johnson. Pediatric osteosarcoma patients are taller than average from birth to age twelve: a report from the Children's Oncology Group. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2532. doi:10.1158/1538-7445.AM2013-2532