Negative Interim FDG-PET Scan Is Predictive of Superior Outcome in T Cell Lymphoma.
Authors: Casulo Carla , Zelenetz Andrew D. , Moskowitz Craig H , Horwitz Steven M. 
Published: October 2019

Abstract
Abstract 1956
Poster Board I-979

Background:
Fluoro-deoxy-glucose positron emission tomography (FDG-PET) is a required staging study for diffuse large B-cell lymphoma and Hodgkin lymphoma. Numerous studies have demonstrated that FDG-PET performed after one to four cycles of multiagent chemotherapy (interim restaging) is predictive of outcome, with relapse rates much higher in patients with positive FDG-PET scans at interim restaging. The prognostic role of FDG-PET in T-cell lymphoma however is unclear and has yet to be well defined. Small retrospective studies have demonstrated FDG-PET avidity of T-cell lymphoma. Our experience confirms that the great majority of patients with mature T or NK lymphomas have FDG-PET avid disease. We hypothesized that the interim FDG-PET (int FDG-PET) may have prognostic importance in patients with T-cell lymphomas as they do in diffuse large B-cell lymphoma and Hodgkin lymphoma.

Methods:
We reviewed our T-cell lymphoma database to identify patients with mature T or NK lymphomas who had FDG-PET scans as part of complete staging at initial diagnosis as well as repeat PET imaging as part of restaging. Inclusion criteria required FDG-PET avid disease at baseline and treatment administered with curative intent.

Results:
We reviewed fifty four patients who met the above criteria. Histologies were as follows: peripheral T-cell lymphoma NOS (N=18), angioimmunoblastic T-cell lymphoma (N=5), anaplastic large cell lymphoma ALK-1- (N=15), anaplastic large cell lymphoma ALK-1+ (N=3), and other subtypes (N=13). Patients received a variety of initial chemotherapy regimens including CHOP (N=18), EPOCH (N=6), CHOP/ICE (N=20) or other treatments provided with curative intent. Twenty two patients were consolidated with high dose therapy and either autologous (N=18), or allogeneic (N=4) SCT. Fifty nine percent were PET negative at interim restaging (32/54), 7.4% were positive (4/54), 22 % were not available (12/54), and 11% had equivocal scans (6/54). Median follow up was 17 months. Median PFS for the entire group was 15 months. Median OS for the entire group was 40 months. The median OS of patients with negative int FDG-PET has not been reached, compared to the OS of patients with positive int FDG-PET of 10.2 months (p<.001). Patients with equivocal int FDG-PET had a median OS of 62 months, which was statistically superior to patients with positive int FDG-PET (p=.02). There was no significant difference in median OS in patients with negative versus equivocal int FDG-PET. Similar to what was observed in OS, the median PFS of patients with negative int FDG-PET has not yet been reached, compared to the PFS of patients with a positive int FDG-PET of 4.8 months (p=<.001). Patients with equivocal int FDG-PET had a statistically improved PFS of 16 months when compared to those with a positive int FDG-PET (p<.01). Patients with equivocal int FDG-PET had similar outcomes to patients with a negative int FDG-PET, and superior to those with a positive int FDG-PET, whose results were very poor.

Conclusions:
In this dataset, interim PET scans are strongly predictive of outcome. Patients with negative int FDG-PET enjoyed significantly longer remissions and better overall survival. Patients with negative int FDG-PET were more likely to receive consolidative therapy, which may contribute to their superior outcomes. This may be a potentially confounding factor. Nonetheless, achievement of a negative int FDG-PET appears to be a reliable predictor of outcome in patients with T-cell lymphomas and may have similar prognostic importance in these patients as they do in diffuse large B-cell lymphoma and Hodgkin lymphoma. It is reasonable to consider int FDG-PET in the restaging of patients with T-cell lymphomas.

Disclosures:
Zelenetz: Millenium Advisory board: Membership on an entity's Board of Directors or advisory committees. Horwitz:Allos Therapeutics, Inc: Consultancy, Research Funding.