The prognostic value of 18-FDG positron emission tomography in T cell non-Hodgkin lymphoma

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) scans are typically positive in patients with T cell non-Hodgkin lymphoma (T-NHL) and can assist in the diagnosis and staging of this uncommon malignancy. Previous studies have suggested that FDG-PET is a useful tool in initial staging of T-NHL; however, there is relatively little evidence for the role of the post-treatment FDGPET in this patient population. Some published studies support the role of a negative post-treatment PET in predicting progression-free survival (PFS) and overall survival (OS), while other studies have found that a negative interim or posttreatment PET does not predict outcome. Recently published guidelines remain ambivalent about the utility of the PET scan in T-NHL, stating ‘there is no clearly defined role for FDG-PET in this disease group’. We aimed to evaluate the predictive value of interim and post-treatment PET scans in T-NHL to determine their effect on PFS and OS. Patients who underwent a PET scan for a diagnosis of T-NHL from 2002 to May 2016 were retrospectively identified by a search of the medical records and NSW Cancer Registry in a single tertiary hospital. Demographics, treatments and survival outcomes were recorded in a de-identified database. Final PET results were correlated with PFS and OS outcomes. Ethics approval was obtained for the study. Kaplan−Meier survival analysis and the log− rank test were used to assess the difference in survival with a P-value of o0.05 to indicate statistical significance. A total of 47 patients were identified as eligible for inclusion, 29 were male (62%), with an average age of 52 years at diagnosis. Out of the total patients, 45 (96%) had an initial PET, 26 (62%) had an interim PET, and 39 (83%) had a post-treatment PET. The majority of patients had advanced disease at diagnosis, with an Ann Arbor stage of III or IV (70%) and an international prognostic index score of 2 or above (60%). The frequency of specific T cell histologies were anaplastic large cell, ALK-1 positive (15%), ALK-1 negative (24%), and unspecified (2%); peripheral T cell lymphoma not otherwise specified (28%); angioimmunoblastic T cell lymphoma (11%); subcutaneous panniculitis-like T cell lymphoma (4%); mycosis fungoides (4%); and others (6%). The majority of patients were treated with CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone, 66%), with other chemotherapy regimens including CHOP with etoposide, HyperCVAD (cyclophosphamide, doxorubicin, vincristine, dexamethasone, methotrexate and cytarabine), SMILE (dexamethasone, methotrexate, ifosfamide, L-asparaginase and etoposide), and cyclosporine with prednisone. Radiotherapy alone was given in 6% of cases. Patients were followed up for a mean of 33.8 months. During the follow-up period, 22 patients progressed (47%) and 20 died (43%). Those with a positive post-treatment PET scan (n= 11) had a median OS of 27.9 months (Figure 1). OS was not reached for those with a negative post-treatment scan (P= 0.0017). The median PFS for those with a positive post-treatment PET scan was 5.2 months, with PFS not reached for those with a negative scan (P= 0.0012; Figure 2). The interim PET scan did not appear to be significant in predicting PFS or OS in our cohort. The post-treatment PET scan appears to be of value in predicting both PFS and OS in T-NHL. Our study is limited by the low patient numbers due to disease rarity and the inherently heterogenous behaviour of the different subtypes of T-NHL. The retrospective, single-centre nature of the study is also an inherent limitation. Nevertheless, this study adds to the growing body of evidence supporting the importance of the post-treatment PET scan in predicting outcomes in T-NHL.