Response Assessment After Induction Therapy in Diffuse Large B Cell Lymphoma (DLBCL): Role of Fluorodeoxyglucose-Positron Emission Tomography (FDG-PET) in Comparison with Computed Tomography (CT).
Authors: Puccini Benedetta , Rigacci Luigi , Pregno Patrizia , Chiappella Annalisa , Alterini Renato , Carrai Valentina , Vitolo Umberto , Bosi Alberto 
Published: October 2019

Abstract
Abstract 4995

Background
The response evaluation is performed by computed tomography (CT) as a standard tool in DLBCL. The introduction the FDG-PET performed for post treatment response assessment of aggressive Non Hodgkin's Lymphoma (NHL) is advised by the Revised International Workshop Criteria (IWC). We explored the predictive value by FDG-PET scan performed at the end of therapy in patients (pts) with DLBCL treated with rituximab-containing regimens .

Patients
From 2003 at 2008 were included 86 pts with DLBCL treated with Rituximab and CHOP or CHOP-like regimens. The FDG-PET and CT was mandatory at baseline and at the end of therapy to include pts in the study. We evaluated the progression free survival (PFS) of pts starting from the time of diagnosis to early relapse or disease progression or last follow-up.

Results
Median age was 60 years (28-78), 40 pts were female and 46 male, 38 pts presented stage I-II and 48 stage III-IV. The International Prognostic Index (IPI) was low in 20% of pts, low-intermediate in 50%, intermediate-high in 28% and high risk in 2%; bulky was reported in 24 pts. Seventy-seven pts attained complete remission (CR) (89%), 8 pts (9%) partial remission (PR) and 1 pts progression disease (2%).
The FDG-PET and CT performed at the end of therapy were both negative in 61 pts (71%); both positive in 9 pts (10%). In the remaining pts the FDG-PET and CT scan performed post therapy were discordant in particular in 13 pts (15%) FDG-PET was negative and CT was positive and in 3 pts (4%) FDG-PET was positive and CT was negative.
Thus the positive predictive value of a FDG-PET at the end of therapy was 63% and the negative predictive value was 87%. The sensitivity and specificity of FDG-PET at the end of therapy were 41% and 94% respectively. The positive predictive value and the negative predictive value of a CT at the end of therapy were 43% and 87% respectively. The sensitivity of CT at the end of therapy was 53% and the specificity was 83%.
Fifthteen out seventy-four patients (20%) with negative FDG-PET progress or relapse within 6 months (median 4 months). Five out twenty (25%) FDG-PET negative bulky disease pts progress or relapse within 6 months moreover four out seventeen (24%) CT negative bulky disease pts progress or relapse. With a median follow-up of 20 months (range 7-83) the overall survival was 86%, and with a median follow-up of 15 months (range 2-78) the PFS was 76%.

Conclusions
FDG-PET shows an high specificity but a very low sensibility in DLBCL. An high rate of false negative FDG-PET was observed in bulky disease patients. We have observed that pts with negative FDG-PET presented a rapid relapse or progression therefore we can consider that probably in non-Hodgkin's lymphoma PET should be performed after four months from the end of therapy to reduce false negative. Obviously larger study are needed but at the moment CT remain the most sensible instrument to define CR in non-Hodgkin's lymphoma.

Disclosures
Vitolo: Roche:.