Multiple Myeloma/drug therapy; Practice Guidelines as Topic; Thalidomide/analogs & derivatives; Anemia/chemically induced; Anemia/physiopathology; Anemia/therapy; Antineoplastic Agents/administration & dosage; Antineoplastic Agents/adverse effects; Antineoplastic Combined Chemotherapy Protocols; Atrial Fibrillation/chemically induced; Atrial Fibrillation/physiopathology; Atrial Fibrillation/therapy; Dose-Response Relationship, Drug; Gastrointestinal Diseases/chemically induced; Gastrointestinal Diseases/physiopathology; Gastrointestinal Diseases/therapy; Humans; Infections/chemically induced; Infections/physiopathology; Infections/therapy; Lenalidomide; Multiple Myeloma/physiopathology; Neutropenia/chemically induced; Neutropenia/physiopathology; Neutropenia/therapy; Renal Insufficiency/chemically induced; Renal Insufficiency/physiopathology; Renal Insufficiency/therapy; Thalidomide/administration & dosage; Thalidomide/adverse effects; Thrombocytopenia/chemically induced; Thrombocytopenia/physiopathology; Thrombocytopenia/therapy; Treatment Outcome; Venous Thromboembolism/chemically induced; Venous Thromboembolism/physiopathology; Venous Thromboembolism/therapy