The evolving role of F-FDG PET scans in patients with aggressive non-Hodgkin's lymphoma.

Functional imaging by (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) is being increasingly incorporated into the evaluation of patients with aggressive non-Hodgkin lymphoma (NHL). Its use for the initial staging in combination with computed tomography has now become standard. PET has recently been included in consensus criteria for response after therapy for Hodgkin lymphoma and aggressive NHL. At the end of therapy, PET has a high positive and negative predictive value (PPV, NPV) for relapse in the pre-rituximab era. However, in the rituximab era, there appears to be a higher rate of false-positive PET scans, making the PPV lower, while the NPV remains high. Interim PET scans are an attractive concept for early evaluation of response, and possibly to guide intensification or de-escalation of therapy. Similar to the end-of-therapy scans, the PPV for mid-therapy scans appears to be low in the rituximab era. Trials testing the modification of therapy based on an interim PET scan are ongoing. For surveillance of patients in remission from aggressive NHL, there is as yet no convincing data that monitoring with PET is superior to traditional surveillance. The evidence to date suggests that a positive PET scan during or after rituximab-based therapy for aggressive NHL should be confirmed by a biopsy if major treatment decisions will be made using the results.