Statistical Analysis
We compared patient demographics between histologic subtypes using
frequencies and central tendency measures. Chi-squared tests determined
differences in proportions between histologic subtypes for lymph node
sampling and lymph node metastases. We calculated unadjusted survival
estimates for OS by histologic subtype using Kaplan-Meier (KM) curves
with log-rank statistics and Gehan-Breslow-Wilcoxon tests when hazards
crossed. Multivariate Cox proportional hazard models estimated the
hazard of death by lymph node sampling and lymph node metastasis
statuses. Models adjusted for known prognostic indicators of OS in
pediatric NRSTS patients, including tumor size and grade, neoadjuvant
chemotherapy, and surgical margins. Histologic subtype significantly
modified the relationship between lymph node sampling and OS, thus we
stratified this regression model by histology. For all regression
models, we confirmed proportional hazards by testing global goodness of
fit for the correlation between Schoenfeld residuals and time. A
Bonferroni corrected p-value <0.0125 was applied for multiple
comparisons amongst stratified histological subtypes; otherwise
p<0.05 was considered significant. All statistical analyses
were performed using R v3.6.1 (R Core Team 2017).16