T-cell Non-Hodgkin's lymphomas are a group of cancers that are usually treated with chemotherapy, radiation therapy, or occasionally surgery. T-cell lymphomas are relatively uncommon and therefore not well studied. Treatment approaches are patterned after the more common B-cell lymphomas. T-cell lymphomas are more likely to relapse following standard therapy than are B-cell lymphomas. New therapies are needed for T-cell lymphomas. In this study, we will administer the drug called lenalidomide as a pill to patients with T-cell lymphoma. The goals are to determine if the drug can induce regression of the cancer, and to determine if the treatment is well tolerated in this patient group. This study will take place at six cancer centres across Canada.