Inclusion Criteria:

- Cohort 1: Patients must be age >18 and < 65 with relapsed or refractory AML or high
risk myelodysplastic syndrome (MDS); high risk MDS is defined as international
prognosis scoring system (IPSS) score of 1.5 or higher; eligible patients will have a
score of 1.5 or higher at any time from diagnosis to screening

- Cohort 2: Patients must be age > 18 with previously untreated AML; favorable
risk AML patients < 60 years of age are excluded; these are defined as core
binding factor (CBF) AML patients and characterized by cytogenetic or molecular
evidence of CBF leukemia; untreated AML patients < 60 years of age must be
negative on screening for CBF leukemia by cytogenetic or molecular analysis
(Note: Prior therapy for MDS is permitted)

- Patients with secondary AML or therapy-related AML are eligible

- No granulocytic sarcoma as the sole site of disease

- No advanced malignant solid tumors or additional active hematologic malignancies

- No active central nervous system (CNS) disease

- Eastern Cooperative Oncology Group (ECOG) performance status 0-2

- Total bilirubin < 2.0 mg/dL

- Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) < 2.5 times upper
limit of normal

- Creatinine < 2.0 mg/dL AND creatinine clearance > 50 mL/min

- Left ventricular ejection fraction (LVEF) ≥ 40%

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective double-method contraception (one highly effective
method and one additional effective method) for ≥ 28 days before, during, and for ≥
28 days after completion of study treatment

- Patients with active infection are eligible provided the infection is under control

- Patients with uncontrolled infection may be enrolled after the infection is
treated and brought under control

- Patients with a comorbid medical illness are eligible provided their life expectancy
attributed to the illness is > 6 months

- No comorbidities that would preclude safety evaluation of study treatment

- No uncontrolled concurrent illness including, but not limited to, any of the
following:

- Symptomatic congestive heart failure

- Unstable angina pectoris

- Serious cardiac arrhythmia

- Psychiatric illness or social situations that would limit compliance with study
requirements

- Myocardial infarction within the past 6 months

- NYHA class III-IV heart failure

- Severe uncontrolled ventricular arrhythmias

- Electrocardiographic evidence of acute ischemia or active conduction system
abnormalities

- No serious medical or psychiatric illness that would interfere with study
participation

- No known HIV positivity

- No history of medically serious allergic reactions or non-hematologic toxicities
attributed to the agents in this study such as lenalidomide or thalidomide or
compounds of similar chemical or biologic composition that are not easily managed, or
patients with a history of cerebellar toxicity to cytarabine

- No history of neurologic toxicity with cytarabine

- Prior lenalidomide, cytarabine, and/or idarubicin allowed provided that the
combination of the 3 agents has never before been administered and that no
lenalidomide has been administered for ≥ 6 months

- Recovered from the adverse events due to agents administered > 4 weeks ago

- More than 2 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin C)
or radiotherapy

- At least 14 days since prior and no other concurrent investigational agents

- No concurrent palliative radiotherapy

- No other concurrent commercial agents or therapies administered with the intent to
treat the patient's leukemia