Interim fluorodeoxyglucose positron emission tomography for early response assessment in diffuse large B cell lymphoma: where are we now?

Fluorodeoxyglucose (FDG)-positron emission tomography (PET) has been established in response assessment after treatment of diffuse large B cell lymphoma (DLBCL) and has been incorporated in the International Workshop Criteria (IWC). Early response assessment is increasingly being used in trials and clinical practice with the hope that it has a greater power to discriminate between good and poor prognosis patients at an earlier point in time. Early data have been very promising and suggest that PET after two to three cycles predicts progression-free survival with high accuracy. Early prediction of prognosis has the potential of enabling early treatment tailoring according to the individual prognosis. Studies are yet to be done to examine the effect of changing therapy early on the basis of poor metabolic response. However, the prognosis of responders/non-responders has been different in various studies, with few recent studies casting some doubt on the value of interim PET. Some of these differences are due to variability in patient populations and treatment protocols. However, there are also important factors related to the methodology of PET scanning and the criteria used to assess response. There is a need for a consensus on a uniform methodology for the use of interim PET both in clinical trials and routine clinical practice. This article critically reviews the current status and suggests future questions for further research.