Comparison of Pixantrone + Rituximab With Gemcitabine + Rituximab in Patients With Aggressive B-cell Non-Hodgkin Lymphoma or Follicular Grade 3 Lymphoma Who Have Relapsed After Therapy and Are Not Eligible for Stem Cell Transplant

Eligible patients will be randomized to treatment with pixantrone plus rituximab or gemcitabine plus rituximab in up to six 28-day cycles. At the time patients experience progressive disease during study treatment, early follow- up, or intermediate follow-up, they enter the survival follow up period. Patients who complete study treatment or discontinue study treatment for any other reason will participate in the follow-up periods. Early Follow-Up: After treatment completion or discontinuation, patient will enter a 24-week follow-up period. Intermediate Follow-Up: After completing the 24-week early follow-up period, patient will enter an additional 72-week follow-up period. Survival Follow-Up: All patients will be monitored for survival.