Dose-finding of Lenalidomide as Maintenance in Multiple Myeloma

Inclusion Criteria: * Understand and voluntarily sign 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 * Multiple myeloma patients who received allogeneic stem cell transplantation (100 to 180 days ago) * No active acute GvHD (grade II - IV) * No active infectious complications * ECOG performance status of \< 2 at study entry * Laboratory test results within these ranges: * Absolute WBC count \> 3.0 x 10\^9/l * Platelet count \> 80 x 10\^9/l * Serum creatinine \< 1.5 mg/dl * Total bilirubin \< 1,5 mg/dl * AST (SGOT) and ALT (SGPT) \< 3 x ULN * Females of childbearing potential must agree to use two reliable forms of contraception simultaneously or to practice complete abstinence from heterosexual intercourse for at least 28 days before starting study drug, while participating in the study and at least 28 days after discontinuation from the study. * male subjects must agree to use a latex condom during sexual contact with females of childbearing potential while participating in the study and for at least 28 days after discontinuation of study drug * 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 Exclusion Criteria: * Any serious medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from signing the informed consent form * pregnant or breast feeding females * use of any other experimental drug or therapy within 28 days of baseline * known hypersensitivity to thalidomide * concurrent use of other anti-cancer agents or treatments * known positive for HIV of infectious hepatitis, type A, B, or C