Phase II of Lenalidomide After Salvage Therapy in R/R Non-Hodgkin T-cell Lymphoma

Inclusion Criteria: 1. The following subtypes of T-cell lymphoma histologically diagnosed based on WHO classification: * Peripheral T-cell lymphoma, not otherwise specified * Angioimmunoblastic T-cell lymphoma * Anaplastic large cell lymphoma, ALK-/+ * Enteropathy-associated T-cell lymphoma * Monomorphic epitheliotropic intestinal T-cell lymphoma * Subcutaneous panniculitis-like T-cell lymphoma * Cutaneous T-cell lymphoma including mycosis fungoides and sezary syndrome 2. Relapse or progression after one or more previous therapies. 3. Partial response or more to a salvage therapy and at least 4 cycles of that salvage therapy at the time of participation in the clinical study. 4. Where autologous stem cell transplantation is unattainable due to poor physical conditions over 65 years of age or secondary transplantation is unattainable due to relapse after primary autologous stem cell transplantation. 5. Non-pregnant female patients who satisfy the following: \- Natural menopause for at least 24 consecutive months before registering for the study or patients who had undergone hysterectomy or bilateral oophorectomy. 6. Male patients who can satisfy the following even if they are surgically infertile (with vasectomy): * Men must use an effective method of contraception during participation in the clinical test and for up to 4 weeks after administration. * Men must use condoms during administration of clinical drug, during temporary suspension of dosage, and for up to 4 weeks after administration if their partners are pregnant and not using an appropriate form of contraception (even after vasectomy). * Men must not donate their sperms during administration of clinical drug and for up to 4 weeks after administration and must immediately notify the researchers if their partners are pregnant during administration of clinical drug or right after suspending administration. * Must comply with the control plans for Lenalidomide (Appendix G). 7. 0 - 2 points in performance ability based on the classification of the eastern Cooperative Oncology Group (ECOG). 8. Appropriate condition of bone marrow, kidney, and liver. * White blood cells ≥ 4,000/μL * Neutrophes ≥ 1,500/μL * Platelets ≥ 75,000/μL (possible if ≥ 50,000/μL in case of intrusion in bone marrow) * Hemoglobin ≥ 9.0 g/dL (examination value is possible after correction through blood transfusion.) * Total bilirubin ≤ 1.5 x normal max. * AST/ALT ≤ 2.5 x normal max. * Creatinine clearance ≥ 50 mL/min (Cockcroft-Gault formula) 9. If the impact of all toxicity from the previous therapy is below Grade 1 based on Common Terminology Criteria for Adverse Events, Version 4.03. 10. Patients who are thought to perform and comply with the clinical test plan based on researcher's judgment. 11. Patients who have voluntarily agreed to participate in the clinical test and signed the consent. 12. Patients who have agreed to donate tissue slides and peripheral blood samples for participation in the clinical study. 13. In case of healthy Type B hepatitis carriers, patients are participatory if they can also undergo preventive antiviral treatment. Exclusion Criteria: 1. Anyone classified into a histological subtype outside the selection criteria; 2. When autologous or allogenic stem cell transplantation is planned after salvage therapy; 3. Patients with symptomatic or uncontrolled angina pectoris or congestive heart failure, arrhythmia requiring chemotherapy, or major hazards anticipated due to clinically significant myocardial infarction that occurred 6 months in prior to participating in this clinical test; 4. In case of an infection exceeding Grade 2 under Common Terminology Criteria for Adverse Events, Version 4.03; 5. Anyone with an accompanied disease that is severe and uncontrolled; 6. Anyone with uncontrolled active Type B or C hepatitis (excluding healthy Type B hepatitis carriers who can be controlled by preventive antiviral agents); 7. Anyone infected with human immunodeficiency virus (HIV); 8. Anyone with allogenic organ transplantation or allogenic stem cell transplantation; 9. Anyone with history of a malignant tumor excluding the following diseases: * Anyone who has not received treatment for the target tumor or has not had any disease at least for the past 5 years; and * Anyone who has spent at least 1 year since complete removal of basal cell carcinoma/squamous cell carcinoma or successful treatment of cervical intraepithelial neoplasia; 10. Serious gastrointestinal bleeding exceeding Grade 2 under Common Terminology Criteria for Adverse Events, Version 4.03 within 30 days before screen; 11. Thrombosis or embolism within 6 months before screen; 12. If it is impossible to administer the clinical drug due to intrusion into the central nervous system (except for cases where the drug can be administered; 13. Any patient who is hypersensitive to this drug or a substance in this drug (ex: angioedema, Stevens-Johnson syndrome, toxic epidermal necrolysis, etc.); 14. Anyone with genetic problems, including galactose intolerance, Lapp lactase deficiency, and glucose-galactose malabsorption; 15. Anyone in an unstable state that may harm a patient's safety and compliance with the test; 16. Any patient with seizure disorder that requires drug administration; 17. Any drug abuse or medical, mental, or social disorder that may affect a patient's participation in clinical test or evaluation of clinical test results; and 18. Women who may be pregnant: * Anyone who has not undergone hysterectomy or bilateral oophorectomy and has not reached natural menopause for at least 24 consecutive months (not including no menstruation after anti-cancer treatment) (in that words, had menstruation anytime within the past 24 months).