Utility of FDG-PET in predicting the histology of relapsed or refractory lymphoma.

18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) is a valuable prognostic tool in modern lymphoma care. In this study, we explored the use of quantitative FDG-PET parameters in predicting the histology of suspected relapsed or refractory (R/R) lymphoma. We retrospectively analyzed 290 FDG-PET scans performed for suspected R/R lymphoma. FDG-PET parameters measured were maximum and mean standardized uptake value (SUVMax and SUVMean), total metabolic tumor volume, and total lesion glycolysis (TLG). Receiver operating characteristic curve analysis was used to obtain the optimal thresholds that best discriminate (1) benign vs R/R lymphoma, (2) indolent vs aggressive non-Hodgkin lymphoma (NHL), and (3) aggressive transformation of indolent NHL. We found that although all 4 FDG-PET parameters discriminated R/R lymphoma from benign histology, TLG was the best performing parameter (optimal cut-off ≥245, sensitivity 63%, specificity 86%, positive predictive value [PPV] 97%, negative predictive value [NPV] 30%, area under the curve [AUC] 0.798, and P < .001). SUVMax discriminated aggressive from indolent NHL with modest accuracy (optimal threshold ≥15, sensitivity 46%, specificity 79%, PPV 82%, NPV 38%, AUC 0.638, and P < .001). In patients with a prior diagnosis of indolent NHL, SUVMax was a modest predictor of transformation (optimal cut-off ≥12, sensitivity 71%, specificity 61%, PPV 50%, NPV 78%, AUC 0.676, and P .006). Additionally, SUVMax ≥25 and an increase in SUVMax (ΔSUVMax) from baseline ≥150% were highly specific (96% and 94%, respectively). These FDG-PET thresholds can aid in identification of suspected R/R lymphoma cases with higher likelihood of R/R disease and aggressive transformation of indolent NHL, guiding the necessity and urgency of biopsy.