A Study of PRO95780 in Combination With Rituximab in Patients With Non-Hodgkin's Lymphoma That Has Progressed Following Previous Rituximab Therapy (APM4083g)

Inclusion Criteria: * Signed Informed Consent Form * Age ≥ 18 years * Diagnosis of follicular, CD20-positive B-cell NHL * Progression of disease after an objective response or stable disease lasting \> 6 months following completion of the most recent rituximab-containing regimen * Measurable disease * Life expectancy of \> 3 months Exclusion Criteria: * Grade 3b follicular lymphoma (according to the WHO classification) or histologic transformation from follicular lymphoma to aggressive lymphoma * Prior radiotherapy to a lesion(s) that will be used to assess response unless that lesion(s) shows clear evidence of lymphoma progression at baseline * Radiotherapy to a peripheral lesion within 14 days prior to Cycle 1, Day 1 or radiotherapy to a thoracic, abdominal, or pelvic field within 28 days prior to Cycle 1, Day 1 * Concurrent systemic corticosteroid therapy * Other invasive malignancies within 3 years prior to first study drug administration except for adequately treated basal or squamous cell skin cancer, in situ carcinoma of the cervix, in situ breast cancer, in situ prostate cancer, limited-stage bladder cancer, or other cancers from which the patient has been disease-free for at least 3 years. * History or evidence on physical examination of central nervous system (CNS) disease * Prior treatment with agonistic DR4 or DR5 antibodies or Apo2L/TRAIL