Pharmacokinetic (PK) and pharmacodynamic (PD) assessments of ABC294640 will be conducted on Day 1 of Cycle 1. Bone marrow biopsy will be obtained prior to the initiation of ABC294640, at the end of cycle #3 and at the end of cycle #6. In addition to serum protein electrophoresis (SPEP), urine protein electrophoresis (UPEP) and serum free light chain measurement, correlative studies will be performed to measure sphingosine kinase 2 (SK2) activity, sphingosine metabolites, and additional biomarkers in CD138+ myeloma cells.