Clinical trials in pediatric oncology over the past 30 years have led to the situation today where most children with newly diagnosed cancer can be treated effectively, and many are cured. Despite this dramatic improvement in outcome for many children diagnosed with cancer, about 30–40% of children will die of their disease . Although some attempts have been made to improve outcome by increasing the dose intensity of existing therapies, intolerable side effects and marginal increases in cancer cell kill limit this approach. Clearly, effective new anti-cancer agents are necessary to significantly improve the survival and quality of life in children with cancer. Well-organized pediatric Phase I trials to establish the maximum tolerated dose (MTD), and Phase II trials to establish efficacy, are critical to the identification of new anti-cancer agents.