Myelofibroses

This is a phase I, open-label, dose-escalation study to determine the MTD of selumetinib when combined with the standard dose of azacitidine. Treatment will begin within 28 days of screening procedures. Treatment will continue indefinitely, provided that the patient continues to derive benefit. A patient will be taken off study for reasons described in detail in section 3.12 including disease progression, unacceptable toxicity, inter-current illness, withdrawal of consent, or at the discretion of the investigator. Patients will be followed for 12 weeks after the last dose of study drug, until any study treatment related toxicities have stabilized, or until death. The total duration of the study is expected to be approximately 24 months.