The Phase 1 part of the study employs a 6+4 design (no DLT in 6 patients or 1 DLT in 10 patients) and incorporates additional PK information before escalating to the next dose level. If there is unacceptable toxicity or if PK results have exceeded the acceptable exposure levels for the adult equivalent dose, further dose escalation will be prohibited. The Recommended Phase 2 Dose (RP2D) is defined as the dose that results in equivalent(approximately 20% of the adult values) PK exposure to 500 mg/day in adults and with 0 of 6 or <2 DLTs observed out of 10 evaluable patients with Ph+ CML and resistance or intolerance to prior TKI therapy. The 95% CI for DLT-risk with The phase 2 part of the study will enroll the following patient populations.

• Newly diagnosed (ND): newly diagnosed Ph + CML patients in chronic phase (CP) Bosutinib in pediatric CML: ITCC-054/AAML1921
• Resistant/intolerant (R/I): chronic phase or advanced (accelerated (AP) or blast phase (BP) Ph+ CML patients with resistance or intolerance to at least 1 prior TKI.