Role of interim and end of treatment positron emission tomography for response assessment and prediction of relapse in posttransplant lymphoproliferative disorder.

Fluorine-18-fluorodeoxyglucose positron emission tomography (PET) has an established and central role in diagnosis, staging and response evaluation of lymphoproliferative diseases. It has shown a high sensitivity and specificity at diagnosis in posttransplant lymphoproliferative disorders (PTLDs). However, little is known about the performance of interim and end of treatment (EOT) PET in PTLD patients with regards to response assessment, relapse prediction and outcome. We performed a single-center retrospective study in which we analyzed consecutive patients diagnosed with CD20-positive PTLD after solid organ transplantation between 2008 and 2017, who all received risk-stratified sequential treatment according to the PTLD-1 phase II trial. Interim and EOT PET studies were scored according to the Deauville criteria. Forty-one patients were included with median follow-up of 41.5 months (range 1-108). Positive and negative predictive values for disease recurrence were 13% and 85% for interim and 33% and 87% for EOT PET, respectively. There was no significant difference in overall survival, progression-free survival nor time to progression between negative versus positive patients on interim and EOT scans. Negative interim and/or negative end of treatment PET identify PTLD patients with low risk of disease recurrence.