Incidence of post-treatment PET-positivity and relapse in Hodgkin lymphoma patients with a negative interim FDG-PET

Abstract

Background: 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), used for assessment of early response in Hodgkin’s lymphoma (HL) patients, is an accurate predictor of progression-free survival. Is has been suggested that end-treatment PET (PETe) is unnecessary if interim PET (PETi) results are negative. The purpose of this study was to evaluate the incidence and clinical characteristics of HL patients with PETi-negative and PETe-positive scans. Material and Methods: For this purpose we retrospectively analyzed data from HL patients enrolled in seven different nuclear medicine centers worldwide. Scans were read by at least one board certified nuclear physician. PETi-negative was defined as no pathologic FDG uptake at any site, including all sites of previously increased pathologic uptake. PETi minimal residual uptake (MRU) was defined as low-grade FDG uptake, although PETi-MRU scans were considered as PETi-negative scan for the purpose of the analysis. A study was considered PETi-positive in case of focal FDG uptake that could not be attributed to physiological distribution. There was no modification in treatment based on PETi results. The incidence of a PETi-negative scan in combination with a PETe-positive scan was calculated. Results: A total of 868 patients were analysed and after two or three cycles of chemotherapy, 643/868 (74.1%) patients were PETi-negative, and 225/868 (25.9%) were PETi-positive. Of the 643 PETi-negative patients, 7.2% (46/643) showed PETe-positive scans. HL was confirmed in 5.1% (33/643) patients, while 2.2% (14/643) were false positive results. Four of those patients died during follow-up, due to HL complications, with a median follow up of 47 (±24.1) months. Clinical characteristics of the 33 early relapsed patients were investigated (sex; age; pathological subtype; B symptoms; Bulky diseae; Clinical stage; International Prognostic Score). Of those patients, 81.8% (27/33) were treated with ABVD. Radiotherapy was administrated in 12 (33.6%) patients. Of the 13 patients with early stage disease, six (46.1%) were submitted to combined therapy. Of the 14 patients with advanced disease, six (42.8%) were submitted to combined therapy. Conclusion: We conclude that, although a rare occurrence, a small number of HL patients will show recurrent signs of disease at the end of treatment, despite a negative PETi. Thus, there is at present not evidence for the omission of PETe. PETe should still be performed as part of the patient's management plan , in order to identify these patients who need additional therapy.