RecruitingPhase 2Drug trialSirolimus in Combination With Metronomic Chemotherapy in Children With High-Risk Solid TumorsThe primary objective of this study is to improve the 2-year progression-free survival in children with high-risk solid tumors who are administered a maintenance regimen with continuous sirolimus administered on a backbone of metronomic chemotherapy following the completion of "standard" therapy, as compared to high-risk solid tumor patients treated with observation alone following completion of "standard" therapy.