Tailoring Treatment for B Cell Non-hodgkin's Lymphoma Based on PET Scan Results Mid Treatment

This is a phase II trial investigating tailoring first-line therapy for advanced stage diffuse large B-cell NHL (DLBCL) based on a mid-treatment 18F-FDG- positron-emission tomography (PET) scan result. More than half of all patients with DLBCL can be cured with 6-8 cycles of standard R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone). Patients who are not cured with R-CHOP have a very poor prognosis. This study will assess whether patients who are likely to fail R-CHOP, as predicted by a mid-treatment PET scan, can have an improved outcome if switched to a standard salvage regimen R-ICE (rituximab, ifosfamide, carboplatin, etoposide). Objectives: * To assess the efficacy of tailoring first-line therapy based on a mid- treatment PET scan result for patients with advanced stage DLBCL. * To assess the progression-free survival (PFS) in patients with advanced stage DLBCL who have a negative mid-treatment PET scan and receive standard therapy with six cycles of CHOP-R and patients with a positive mid-treatment PET scan who receive four cycles of CHOP-R followed by four cycles of R-ICE chemotherapy. * To assess the overall survival (OS) in patients with advanced stage DLBCL who have a negative mid-treatment PET scan and receive standard therapy with six cycles of CHOP-R and patients with a positive mid-treatment PET scan who receive four cycles of CHOP-R followed by four cycles of R-ICE chemotherapy.