<qa>  What is the name of the study that is designed to explore the safety, maximum tolerated doseThis is a 5-part, open-label, Phase 11b multicenter, dose escalation study in pediatric patients with relapsed refractory solid tumors; 2 primary CNS tumors; 3 neuroblastoma; 4 non-neuroblastoma, extracranial solid tumors with NTRK123, ROS1 or ALK gene rearrangements; and 5 patients who are otherwise eligible but unable to swallow capsules. The study is designed to explore the safety, maximum tolerated dose MTD or recommended Phase 2 dose RP2D, pharmacokinetics, and antitumor activity of entrectinib. 