Patient characteristics and confounders: Patient characteristics (demographics, comorbidities); Disease-related characteristics (duration, myeloma stage and risk, details regarding previous therapy and response, functional status, quality of life); Other drugs (Number of drugs, pills and potential interactions with lenalidomide). We will use an adaptation of the questionnaire from the "BRIGHT" study (which assesses barriers to immunosuppressive medication adherence in heart transplant recipients) to assess barriers to adherence in this patient cohort.