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.