This pilot Phase II study is designed to evaluate the efficacy and tolerability of crenolanib in two cohorts of AML patients with FLT3 activation mutations (patients whose leukemia has recurred after prior chemotherapy not including a FLT3 TKI and patients whose leukemia has progressed after prior therapy with a FLT3 TKI).

This is a Phase II open label study of crenolanib besylate. This study will enroll subjects with relapsed acute myeloid leukemia (AML) with FLT3 activating mutations. Two cohorts of patients will be enrolled: those whose AML has recurred after prior chemotherapy without a FLT3 TKI, and those whose AML has progressed after prior therapy with FLT3 TKIs. Subjects will take Crenolanib besylate at 100 mg TID until disease progression, death, or unacceptable toxicities. Concurrent hydroxyurea is permitted during the first 28 days of study therapy.

Inclusion Criteria:

• Confirmed primary AML relapsed or refractory after prior therapy, AML secondary to antecedent chemotherapy or radiation therapy, or AML due to prior myelodysplastic syndrome (MDS)/ myeloproliferative neoplasm (MPN) as defined by WHO criteria with presence of either FLT3 ITD and/or other FLT3 activating mutations
• Patients with secondary AML should have failed no more than two (2) prior regimens
• Patients with antecedent MDS/MPN, defined by WHO criteria, without any prior therapy for AML, regardless of the number of therapies for MDS/ MPN
• Patients with primary AML should have received no more than two (2) prior cytotoxic containing salvage regimens. Reinduction with the same regimen or stem cell transplant will not be considered a separate salvage regimen. Change of drugs will be considered a salvage regimen. Unlimited FLT3 TKI therapy (even in combination with cytotoxics/hypomethylating agents) is allowed for patients enrolled in cohort B
• Patients must have tested positive for FLT3-ITD and /or other FLT3 activating mutations within 30 day screening period
• Males and females age ≥18 years
• ECOG PS 0-2
• Adequate liver function, defined as bilirubin ≤1.5x ULN, ALT ≤3.0x ULN, and AST ≤3.0x ULN
• Adequate renal function, defined as serum creatinine ≤1.5x ULN
• Recovery from non-hematological toxicities of prior therapy (including HSCT) to no more than grade 1 (except alopecia)
• Subjects should have received no anti-leukemic therapy (except hydroxyurea) prior to the first dose of crenolanib as follows: for 14 days for classical cytotoxic agents and for five times the t1/2 (half-life) for FLT3 inhibitors and antineoplastic agents that are neither cytotoxic nor FLT3 inhibitors (e.g. hypomethylating agent or MEK inhibitor)
• Negative pregnancy test for WOCBP
• Able and willing to provide written informed consent.

Exclusion Criteria:

• Absence of a FLT3 activating mutation
• <5% blasts in blood or marrow at screening
• Concurrent chemotherapy, or targeted anti-cancer agents, other than hydroxyurea
• Patient with concurrent severe and/or uncontrolled medical conditions that in the opinion of the investigator may impair the participation in the study or the evaluation of safety and/or efficacy
• HIV infection or active hepatitis B (defined as hepatitis B surface antigen positive) or C (defined as hepatitis C antibody positive)
• Known clinically active central nervous system (CNS) leukemia
• Patients less than 30 days post HSCT
• Subjects who have clinically significant graft versus host disease requiring treatment and /or have >grade 2 persistent non hematological toxicity related to transplant
• Prior crenolanib treatment for a non-leukemic indication
• Major surgical procedures within 14 days of Day 1 administration of crenolanib.
• Unwillingness or inability to comply with protocol.