Newly diagnosed DLCL patients will have baselne FDG-PET as part of initial staging (PET-1). Patients will then undergo 2 cycles of chemotherapy with R/CHOP. 14 to 21 days following cycle 2 of R/CHOP, patients will undergo repeat FDG-PET scan (PET-2). They will then complete therapy as planned. Following completion of therapy, standard response assessment will be performed, including CT scans of the chest, abdomen and pelvis and FDG-PET scan (PET-3).

Inclusion Criteria:

• Patients must have histologically or cytologically confirmed diagnosis of CD20+ diffuse large B cell lymphoma (LBCL) of any stage, including subtypes mediastinal large B cell, centroblastic, immunoblastic, T cell rich B cell and anaplastic B cell lymphoma
• Patients must have received no prior anti-lymphoma therapy.
• Age >18 years.
• Patients must have a treatment plan to include R/CHOP or R/CHOP followed by radiotherapy.
• Ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

• Patients who have known HIV infection.
• Patients who are, in the opinion of their treating oncologist, unable to undergo R/CHOP chemotherapy.

Newly diagnosed diffuse large b cell lymphoma patients planning to receive 6-8 cycles of R/CHOP chemotherapy.