A Study of ARRY-520 in Patients With Relapsed or Refractory Multiple Myeloma

Key Inclusion Criteria (Part 3): * Patients should have received at least two prior treatment regimens. * Confirmed refractory MM (measurable disease) or PCL. Patients must be refractory to treatment with both lenalidomide/dexamethasone and bortezomib/dexamethasone (or to treatment with bortezomib/lenalidomide/dexamethasone), defined as documented progressive disease on therapy or within 60 days of completing treatment with these regimens. * Previously received adequate alkylator therapy. * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1. * Adequate hematology laboratory values without transfusion support within 2 weeks of screening. * Adequate liver and renal function. * Additional criteria exist. Key Exclusion Criteria (Part 3): * Primary amyloidosis. * Concomitant malignancies or previous malignancies with less than a 3-year disease free interval at the time of enrollment (patients with adequately resected basal or squamous cell carcinoma of the skin, carcinoma in situ of the cervix or Stage A low grade prostate cancer may enroll irrespective of the time of diagnosis). * Autologous or allogeneic stem cell or bone marrow transplant within 3 months prior to first dose of study drug. * Cytotoxic therapy or monoclonal antibodies within 21 days prior to first dose of study drug. * Radiotherapy within 21 days prior to first dose of study drug (if the radiation portal covered ≤ 5% of the bone marrow reserve, the patient may be enrolled irrespective of the end date of radiotherapy). * Corticosteroid doses \> 10 mg/day of prednisone or equivalent within 2 weeks prior to first dose of study drug. * Known positive serology for the human immunodeficiency virus (HIV), hepatitis B and/or active hepatitis C. * Additional criteria exist.