End-of-Treatment Positron Emission Tomography After Uniform First-Line Therapy of B-Cell Posttransplant Lymphoproliferative Disorder Identifies Patients at Low Risk of Relapse in the Prospective German PTLD Registry

Background. Fluorine-18 fluorodeoxyglucose (18F-FDG)-positron emission tomography (PET) is a recommended standard in the staging and response assessment of 18F-FDG-avid lymphoma. Posttransplant lymphoproliferative disorder (PTLD) can be detected by 18F-FDG-PET at diagnosis with high sensitivity and specificity. However, the role of response assessment by end-of-treatment (EOT) PET has only been addressed in small case series. Methods. We performed a retrospective, multicenter study of 37 patients with CD20-positive PTLD after solid organ transplantation treated with uniform, up-to-date, first-line protocols in the prospective German PTLD registry who had received EOT 18F-FDG-PET between 2006 and 2014. Median follow-up was 5.0 years. Any nonphysiological 18F-FDG uptake (Deauville score greater 2) was interpreted as PET-positive. Results. By computed tomography (CT) final staging, 18 of 37 patients had a complete response, 18 had a partial response and 1 patient had stable disease. EOT PET was negative in 24 of 37 patients and positive in 13 of 37 patients. The positive predictive value of EOT PET for PTLD relapse was 38%, and the negative predictive value was 92%. Time to progression (TTP) and progression-free-survival were significantly longer in the PET negative group (P = 0.019 and P = 0.013). In the 18 patients in a partial response by CT staging, we noted highly significant differences in overall survival (P = 0.001), time to progression (P = 0.007), and progression-free survival (P < 0.001) by EOT PET. Conclusions. Even without baseline imaging, EOT PET in PTLD identifies patients at low risk of relapse and offers clinically relevant information, particularly in patients in a partial remission by CT staging