The Role Of 18F-FDG PET/CT For Staging and Response Assessment To Chemotherapy In Marginal Zone Lymphoma.
Authors: Mercado Marta Ruiz , Cruz Estrella Carrillo , Vicente Fátima de la Cruz , Marín-Oyaga Víctor A , Rodríguez María Solé , Borrego-Dorado Isabel , Tocino Ildefonso Espigado , Vázquez-Albertino Ricardo , Pérez-Simón Jose Antonio 
Published: October 2019

Abstract

Introduction
Marginal Zone Lymphoma (MZL) is an indolent lymphoma in which the use of PET/CT is poorly explored and also controversial due to the heterogeneous 18F- FDG avidity described in these types of lymphoma. Our aim in the present study is to evaluate the role of 18F-FDG-PET/ CT (PET/CT) in comparison to CT with intravenous contrast enhancement at initial staging and response assessment to chemotherapy in these patients.

Methods and Materials
A retrospective single-center study that included 34 patients, diagnosed of MZL between 1998 and 2012, with at least one PET/CT available. A total of 55 PET/ CT were performed: 25 at initial diagnosis, 19 for first- line response assessment, 6 in relapse and 5 after relapse- treatment. Locations of involved areas were registered comparing staging CT and PET/CT and were classified as discrepancy or not.

Results
Patients´ baseline characteristics are shown in table 1. At diagnosis, all patients presented with at least one abnormal focal FDG uptake except for one, which reflected a sensitivity of 96%. Median SUVmax was higher in nodal marginal zone lymphoma (NMZL) and extranodal marginal zone lymphoma (ENMZL): 6,1 (4- 8,4) and 6,9 (2- 13,8) respectively, in comparison to splenic marginal zone lymphoma (SMZL) 3,4 (3,2- 3,6) p=0,3. SUVmax was much higher in a patient with histological transformation to a DLBCL (SUVmax 37). Among 17 patients with both radiological imaging at the time of diagnosis, there were 8 patients (47%) with more involved areas demonstrated by PET/ CT than by CT alone, 75% of them were extranodal lesions. PET/CT upstaged 5 patients but in only 2 of them entailed a change in therapeutic management. Four patients did not show FDG avidity by PET/CT in some areas suspected to be involved by CT, what generated a CT sensitivity of 76%.
Overall, CR was attained in 24 patients (66%) with 5-y OS 78%. Among 19 patients with a PET/CT available for first-line response assessment, responses were: 12 CR, 2 PR, 1PD and isolated residual lesions in 4 patients. Progression was documented in 2 of the 4 patients with residual lesions which were considered positive, and in 2 patients who maintained remission, the image was interpreted as a false positive (FP). The response assessment was performed by both radiological imaging in 13 patients. Discrepancies were found in 4 cases: CT showed CR in 3 patients while PET/CT detected localized residual disease and in another patient, CT showed stable disease whereas PET/CT demonstrated CR.
Overall, none of the patients in CR by PET/CT relapsed. Five-year OS was 100% in contrast to 64% for those patients with a positive PET/CT after completing treatment (p=0,2), with a mean follow-up of 50 months (10-152). The NPV was 100% and PPV was 71% (5/7).
Relapse was detected in 9 patients (37.5%). Six patients had PET/CT for re-staging and 5 for response assessment. All re-staging PET/CT had FDG-avidity with a median SUVmax of 9.9 (4.6-17.2). PET/CT for response after salvage treatment demonstrated 3 CR and 2 localized residual lesions. The NPV and PPV was 100% and 50%, respectively.

Conclusions
MZL shows higher 18F- FDG avidity in NMZL y ENMZL subtypes. PET/CT is more sensitive than CT at initial staging, chiefly in identifying extranodal involvement. Response assessment PET/CT had a NPV of 100% and PPV of 71 and 50% after first and second-line treatment, respectively.

Disclosures:
No relevant conflicts of interest to declare.