Productivity of ¹⁸ F-FDG-PET/CT diagnostic tool in the management of pediatric lymphoblastic lymphoma

BACKGROUND: Lymphoblastic lymphoma (LL) comprises approximately 20% of childhood non-Hodgkin lymphoma (NHL); however, few studies had investigated the role of 18 F-FDG-PET/CT in pediatric LL patients. We aim in this study to assess the role of 18 F-FDG-PET/CT in the initial staging of newly diagnosed pediatric patients with LL as well as in the assessment of response after induction chemotherapy. PATIENTS AND METHODS: A prospective study enrolled biopsy proven newly diagnosed pediatric LL patients presenting in the Children Cancer Hospital Egypt (CCHE) during the period from October 2014 to October 2016. 18 F-FDG-PET/CT was done initially before therapy and after induction chemotherapy in all patients. The patients were followed until the end of April 2018 (mean 23.5 months). RESULTS: All lymphoma involvement lesions (n = 43) were FDG avid and the intensity of nodal FDG uptake was variable. Two patients (11%) had bone marrow (BM) involvement by < 25% blast cells with corresponding positive BM focal uptake in 18 F-FDG-PET/CT (SUVmax = 4 and 4.5). Evaluation post induction phase; CT detected 8 residual lesions in 8 patients (44.4%), while 18 F-FDG-PET/CT detected only 3 Deauville-positive residual lesions in 3 patients (16.6%). No intensification of therapy was done in all post-induction positive patients. Repeated 18 F-FDG-PET/CT at week 18 for post-induction patients revealed cleared all Deauville-positive residual lesions. On the other hand, repeated CT at week 18 detected regression but still residual in 4/8 (50%) post-induction CT lesions with clearance of the rest (50%). CONCLUSION: In initial staging, 18 F-FDG-PET/CT is a useful tool for disease extent evaluation of pediatric LL. Moreover, it could provide a diagnostic hint for BM involvement. 18 F-FDG-PET/CT done after induction therapy has a good negative predictive value with higher specificity than CT alone, but is not an indication for treatment intensification due to false positive results. However, larger sample size is required for better conclusion.