Inclusion Criteria:

- Understand and voluntarily sign an informed consent form.

- Age >=18 years at the time of signing the informed consent form.

- Able to adhere to the study visit schedule and other protocol requirements.

- AML (>/= 20% blasts) including secondary (s)AML (after radio-chemotherapy) with
karyotype abnormalities involving monosomy 5 or del5q or MDS and sMDS RAEB-1 and
RAEB-2 with karyotype abnormalities involving monosomy 5 or del5q or MDS and sMDS
type RA(+/-RS) or RCMD(+/-RS) only with complex karyotype abnormalities involving
monosomy 5 or del5q

- in complete hematological remission documented by bone marrow aspiration within 8-12
weeks after allogeneic HSCT

- All previous cancer therapy, including radiation, hormonal therapy and surgery, must
have been discontinued at least 4 weeks prior to treatment in this study.

- ECOG performance status of
- Laboratory test results within these ranges:

- Absolute neutrophil count >= 1.0 x 10 9/L

- Platelet count >= 100 x 10 9/L

- Serum creatinine <= 2.0 mg/dL

- Total bilirubin <= 1.5 mg/dL

- AST (SGOT) and ALT (SGPT) <= 5 x ULN

- Females of childbearing potential (FCBP)† must agree to use two reliable forms of
contraception simultaneously or to practice complete abstinence from heterosexual
intercourse during the following time periods related to this study: 1) for at least
28 days before starting study drug; 2) while participating in the study; and 3) for
at least 28 days after discontinuation from the study. The two methods of reliable
contraception must include one highly effective method (i.e. intrauterine device
(IUD), hormonal [birth control pills, injections, or implants], tubal ligation,
partner's vasectomy) and one additional effective (barrier) method (i.e. latex
condom, diaphragm, cervical cap). FCBP must be referred to a qualified provider of
contraceptive methods if needed.

- Disease free of prior malignancies for >= 5 years with exception of currently treated
basal cell, squamous cell carcinoma of the skin, or carcinoma "in situ" of the cervix
or breast

- Able to take aspirin (ASA) 100mg daily as prophylactic anticoagulation in case of
concomitant steroid treatment (patients intolerant to ASA may use low molecular
weight heparin).

Exclusion Criteria:

- Any serious medical condition, laboratory abnormality, or psychiatric illness that
would prevent the subject from signing the informed consent form.

- active uncontrolled acute GVHD overall grade 3-4

- Pregnant or breast feeding females. (Lactating females must agree not to breast feed
while taking lenalidomide).

- History of arterial or venous embolism or stroke

- Any condition, including the presence of laboratory abnormalities, which places the
subject at unacceptable risk if he/she were to participate in the study or confounds
the ability to interpret data from the study.

- Use of any other experimental drug or therapy to treat MDS or AML within 28 days of
baseline (patients within a clinical trial evaluating new conditioning regimens are
allowed to participate in the LENAMAINT study)

- Known hypersensitivity to thalidomide or lenalidomide.

- history of erythema nodosum if characterized by a desquamating rash while taking
thalidomide or similar drugs.

- Known positive for HIV or infectious hepatitis, type A, B or C.