For each subject, the study consists of three phases: Pre-randomization phase (14 days), Treatment Phase (12 weeks) and an extension phase where subjects have the opportunity to receive lenalidomide treatment as long as benefit is derived from the drug. Subjects who complete all 12 weeks of the treatment phase may be eligible to initiate (subjects randomized to receive placebo in the treatment phase) or continue to receive lenalidomide therapy (subjects randomized to receive lenalidomide in the treatment phase) in the extension phase. Subjects may continue in the extension phase as long as a benefit is derived from the drug.