The purpose of this study is to determine whether people have genes that make them more likely to respond to chemotherapy and/or have side effects from chemotherapy for diffuse large cell lymphoma.

Upon enrollment in the study, patients will have a blood sample collected for genotyping of the FCGR3A gene (immunoglobulin Fc G receptor IIIa), the ABCB1 gene (ATP Binding Cassette Beta 1; also called MDR1), and other candidate genes. Patients will be treated with R-CHOP for six cycles, which is standard therapy for advanced stage DLCL. Response will be monitored by an FDG-PET scan performed after 2 cycles of R-CHOP and restaging exams performed upon completion of chemotherapy. Gene polymorphisms will be analyzed to establish which polymorphisms predict response to R-CHOP.

Inclusion Criteria:

• Histologically proven diffuse large B-cell non-Hodgkin's lymphoma according to the WHO classification, with measurable or evaluable disease
• No prior therapy for NHL. Patient may be enrolled in this study after the first cycle of R-CHOP if all screening evaluations were performed prior to the first cycle of chemotherapy.
• Ann Arbor stage 3 or 4
• Age greater than or equal to 18 years
• Patient must give written informed consent.
• A patient enrolled in another clinical trial may also enroll in this study if the other trial has an R-CHOP treatment arm and the patient is randomized to the R-CHOP only arm. Registration to this study must occur after randomization in the other trial.

Exclusion Criteria:

• CNS involvement
• Known HIV positive
• T-cell lymphoma or history of indolent NHL
• Patients who will be treated with radiation therapy