This is an open-label, multicenter, Phase Ib study to be conducted at approximately eight sites in Europe and the U.S. designed to evaluate the safety, pharmacokinetics, and activity of SGN-40 when combined with bortezomib in patients with multiple myeloma that is relapsed or refractory after at least one prior systemic treatment regimen.

Inclusion Criteria:

• Age ≥ 18 years
• Documented pathologic diagnosis of multiple myeloma that has relapsed or failed to respond after treatment with at least one prior systemic therapy (other than corticosteroid monotherapy)
• Measurable disease
• At least one prior systemic therapy other than single-agent corticosteroids
• European Union patients must have had prior bone marrow transplant (autologous) or be ineligible for transplant
• If previously received bortezomib, demonstration of clinical response of any duration or stable disease with progression-free interval of ≥ 6 months from the start of that therapy
• If previously received bortezomib, must have recovered from bortezomib-related toxicities and must have a peripheral neuropathy score of Grade ≤ 1, according to the NCI CTCAE v3.0
• If applicable, completion of autologous transplant ≥ 12 weeks prior to Day 1
• Discontinuation of previous anticancer or investigational therapy for ≥ 21 days prior to treatment, or ≥ 90 days prior to treatment for previous monoclonal antibody administration

Exclusion Criteria:

• Prior allogeneic bone marrow transplant
• Other invasive malignancies within 3 years prior to Day 1 except for adequately treated basal cell or squamous cell skin cancer; carcinoma in situ of the cervix, breast, or prostate; or other cancer of which the patient has been disease-free for ≥ 3 years
• Prior anaphylactic reaction to human immunoglobulin administration
• Symptomatic hyperviscosity syndrome
• Active infection requiring parenteral antibiotics within 14 days of Day 1
• Major surgical procedure or significant traumatic injury within 28 days prior to Day 1, or anticipation of need for major surgical procedure during the course of the study
• Clinically significant cardiac dysfunction or other significant organ dysfunction