This is a randomized trial to estimate the activity of R-ICE plus SGN-40 vs. R-ICE plus placebo in patients with DLBCL. The study will assess safety and tolerability and will measure any additional clinical benefit observed in patients receiving SGN-40.

Inclusion Criteria:

• Confirmed diagnosis of de novo or transformed DLBCL, or follicular grade 3b lymphoma.
• Received at least four cycles of first-line therapy with R-CHOP, or equivalent.
• Best clinical response to first-line therapy of stable disease, partial response, or complete response.
• At least one measureable lesion that is both greater than or equal to 1.5cm by radiographic imaging and by positive FDG-PET scan.

Exclusion Criteria:

• Leptomeningeal or central nervous system lymphoma.
• Received any therapy for relapsed or progressive disease except for local radiation, steroids, or rituximab.
• Received a hematopoietic stem cell transplant.