Does 18F-Fluorodeoxyglucose Outperform 18F-Fluorothymidine When Using Positron Emission Tomography in Predicting Transformation of Indolent Non-Hodgkin's Lymphoma,
Authors: Wondergem Marielle , Zijlstra Josee , Hoetjes Nikie , Chamuleau Martine ED , Zweegman Sonja , Huijgens Peter C. , Boellaard Ronald , Hoekstra Otto s 
Published: October 2019

Abstract
Abstract 3658
Introduction Patients (pts) with transformed NHL have an extremely poor prognosis. However when diagnosed at an early stage outcome may be better, making early diagnosis crucial. Nowadays, transformation is diagnosed using biopsy of a lymph node when it starts growing rapidly or when the patient develops B symptoms or hypercalcemia. These pts often have advanced disease and diagnosis may be delayed because the lymph node biopsied is not representative. Positron emission tomography (PET) might be of value here: the commonly used tracer 18F-fluorodeoxyclucose (FDG)-PET can distinguish between indolent and aggressive lymphoma, but with considerable overlap in Standard Uptake Values (SUV). However, 18F-fluorothymidine (FLT) is thought to more directly reflect proliferation. We performed a head-to-head comparison of FDG and FLT PET in pts with indolent and transformed lymphoma to explore which tracer qualifies best for future research in timely diagnosis of transformation.
Materials and methods Pts were selected based on histology: either follicular lymphoma or transformed lymphoma (defined as diffuse large B cell lymphoma diagnosed in a patient with former or simultaneous diagnosis of follicular lymphoma in a lymph node).In each patient two PET scans were made, one with FDG and one with FLT, maximum one week apart, before any treatment.Scans were made on the Philips Gemini TF PET-CT camera, 1 hour after injection of 185 MBq of FDG or FLT.Uptake (we present data as SUVmax normalized to body weight) was measured in all lymph nodes ≥ 2 cm (minimizing partial volume effects).
Results 17 pts with indolent lymphoma and 10 with transformed lymphoma were included. Median age was 59 years (range 35–81) and a median of 9 lymph nodes were measured per patient (range 2–23). Between patients, SUVmax in the lymph node with the highest uptake for both FDG (p=0.01) as well as FLT (p=0.04) uptake was significantly higher in transformed lymphoma. For FDG values ranged from 4,9 to 19,6 in indolent and from 9,6 to 29,9 in transformed lymphoma, for FLT values were respectively 3,6 to 16,6 and 5,45 to 16,3. Accordingly, between patients, we found considerable overlap between highest values for indolent and transformed lymphoma with either tracer, making the determination of a cut off level for transformation difficult. The data suggest that, at least for FDG, the range between the lymph node with the highest and the lowest uptake within one patient was the best criterium to identify the transformed lymphomas, with significantly higher ranges for transformed lymphoma (p<0,001; ranges from 0,34 to 11,3 for indolent and from 5,1 to 20,2 for transformed lymphoma). A cut off value of 7 (highest SUVmax minus lowest SUVmax) has a positive predictive value of 90% for transformation.
Conclusion Uptake of both FDG and FLT are significantly higher in transformed lymphoma than in indolent lymphoma. However, FDG-PET may better distinguish between indolent and transformed lymphoma. For further research, intrapatient heterogeneity of FDG uptake qualifies as a potential marker of transformation, ultimately to facilitate timely diagnosis of transformation and improved patient outcome.

Disclosures:
No relevant conflicts of interest to declare.