Inclusion Criteria:

- Relapsed primary AML or AML secondary to myelodysplastic syndrome with an expected
survival of 3 months or greater

- Presence of a FLT3-D835 activating mutation irrespective of presence of other
mutations like FLT3-ITD

- Age ≥18 years

- ECOG PS 0 - 2

- Adequate liver function, defined as total or direct bilirubin ≤1.5x ULN, ALT ≤3.0x
ULN, AST ≤3.0x ULN. Exceptions for ALT and AST restrictions will be made in the
setting of documented liver involvement with leukemia.

- 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)

- In the absence of rapidly progressing leukemia, subjects should have received no
anti-leukemic therapy (except hydroxyurea) for 2 weeks (for classical cytotoxic
agents and FLT3 inhibitors; 4 weeks for radiation) prior to first dose of crenolanib.

- Negative pregnancy test for women of childbearing potential.

- Able and willing to provide written informed consent.

Exclusion Criteria:

- Absence of FLT3-D835 activating mutation

- <5% blasts in blood or marrow at screening

- Concurrent chemotherapy, systemic immunosuppressants, 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 or C

- Subjects who have had HSCT and are within 60 days of an allogeneic or autologous
transplant, and/or have clinically significant graft-versus-host disease requiring
systemic treatment.

- Unwillingness or inability to comply with protocol.