Page 34 - Wondergem

Chapter 2
Abstract
Considering the different treatment strategy for transformed follicular lymphoma (TF) as opposed to follicular lymphoma (FL), diagnosing transformation early in the disease course is important. There is evidence that 18F-FDG has utility as biomarker of transformation. However, quantitative thresholds may require inclusion of homogeneous NHL subtypes to account for differences in tracer uptake per subtype. Moreover, since proliferation is a hallmark of transformation, 18F-FLT might be superior to 18F-FDG in this setting. To define the best tracer for detection of transformation of FL, we performed a prospective a head-to-head comparison of 18F-FDG and 18F-FLT in patients with FL and transformed FL.
Methods: 18F-FDG- and 18F-FLT-PET scans were performed in 17 patients with FL and 9 patients with transformed lymphoma. We measured highest SUVmax, defined as the lymph node with the highest uptake per patient and SUVrange, defined as the difference between the SUVmax of the lymph node with the highest and lowest uptake per patient. To reduce partial volume effects only lymph nodes larger than 3cc (A50 isocontour) were analyzed. Scans were made 1 hour after injection of 185 MBq of 18F-FDG or 18F-FLT. To determine the discriminative ability of SUVmax and SUVrange of both tracers for transformation of FL, ROC curve analysis was performed.
Results: Highest SUVmax was significantly higher for TF compared to FL for both 18F-FDG and 18F-FLT (p<0.001). SUVrange was significantly higher for TF as compared to FL for 18F-FDG (p=0.029) and not for 18F-FLT (p=0.075). The ability of 18F-FDG to discriminate between FL and TF was superior to that of 18F-FLT for both the highest SUVmax (p=0.039) and SUVrange (p=0.012). The cut-off value for highest SUVmax of 18F-FDG aiming at 100% sensitivity with a maximum specificity was found to be 14.5 ( corresponding specificity 82%). For 18F-FLT these values were 5.1 and 18%, respectively. When applying the same method to SUVrange, cut-off values were 5.8 for 18F-FDG (specificity 71%) and 1.5 for 18F-FLT (specificity 36%).
Conclusion: our data suggest that 18F-FDG PET is a better biomarker for transformed FL than 18F-FLT PET. The proposed thresholds of highest SUVmax and SUVrange should be prospectively validated.
(this trial was registered: NTR code 1487)
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