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.