Importance of [18F]fluorodeoxyglucose-positron emission tomography scanning for the monitoring of responses to immunotherapy in follicular lymphoma

We prospectively investigated the use of [F-18]fluorodeoxyglucose (FDG)-positron emission tomography (PET) to kinetically monitor cell activation in six follicular lymphoma patients vaccinated with tumor lysate-pulsed autologous dendritic cells. PET revealed additional initial nodes suggestive of lymphoma, that were of less than 10 mm, of diameter on computed tomography, and documented disease progression with sensitivity, even within loci with no significant variations of CT findings. Although tracer fixation was not observed in the inguinal nodes draining the dendritic cell intradermal injection sites in the six patients, a transient marked increase in FDG uptake within malignant nodes was observed early after vaccine administration in a patient who achieved complete remission. In non-responding patients, we observed a continuous increase of FDG uptake associated with an increase in the size and number of pathological nodes/locus, or of involved loci. FDG-PET is a non-invasive imaging procedure that might be of crucial interest to detect cell responses induced by immunotherapies.