Serum Vitamin D Levels and Peripheral Neuropathy Among Multiple Myeloma Patients

Inclusion Criteria: * Voluntary written informed consent before performance of any study-related procedure not part of normal medical care, with the understanding that consent may be withdrawn by the subject at any time without prejudice to future medical care. * Prior diagnosis of multiple myeloma based on standard criteria (Durie 1986) * Received consecutive, prior treatment for MM with a regimen consisting of at least 16 consecutive weeks of bortezomib or 16 consecutive weeks of thalidomide prior to the Day of Assessment * The 16 weeks of consecutive treatment must have included at least one of the following doses and schedules: * Bortezomib: ≥ 1.0 mg/m² dosed 3 or more times per each 4-week period * Thalidomide: ≥ 50 mg/day dosed daily * The qualifying regimen may include both bortezomib and thalidomide. However, the above inclusion requirements need only be satisfied by either one of the agents. * Age ≥18 years at the time of signing the informed consent form * Able to adhere to the study visit schedule and other protocol requirements Exclusion Criteria: * Plasma cell dyscrasia with polyneuropathy, organomegaly, endocrinopathy, monoclonal protein (M-protein) and skin changes (POEMS) syndrome (Bardwick 1980) * Plasma cell leukemia * Primary amyloidosis * Vitamin D level assessment occurring within the 12 months preceding the Day of Assessment * Vitamin D non-dietary oral supplementation \> 1200 IU per day for \> 30 total days within the 12 month period preceding the Day of Assessment * Serious medical or psychiatric illness likely to interfere with participation in this clinical study. * Any serious medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from signing the informed consent form * Any condition, including the presence of laboratory abnormalities, which places the subject at unacceptable risk if he/she were to participate in the study or confounds the ability to interpret data from the study.