The Role of 18-FDG PET/CT in Managing Unclassifiable Mediastinal B-Cell Lymphoma -Gray Zone Lymphoma

Abstract

Introduction: Gray zone lymphoma (GZL) is a recently described disease entity. The clinical features and treatment of GZL remain to be defined because of its recent identification and rarity. Positron Emission Tomography (PET) has become the gold standard for response assessment in most FDG-avid lymphomas. Clinicians currently consider PET the gold standard in managing LZG, exhibiting excellent sensitivity and specificity. Objectives: The study aimed to highlight the contribution of 18FDG PET in the management of gray zone lymphoma. Materials and Methods: A retrospective descriptive and analytical study of 4 patients with GZL was conducted, followed up in the Hematology Department at Farhat Hached University Hospital of Sousse, who underwent 18 FDG PET scans in the Nuclear Medicine Department at Sahloul University Hospital in Sousse. Four patients were included in the study. All patients were adults, ranging from 19 to 33 years. The study was conducted between December 2018 and October 2023. The FDG-PET scans were scored according to the 5-point Deauville scoring (DS) system. Results: The discovery circumstances were variable, mainly a tumor syndrome. Two patients had B symptoms at diagnosis. The 9 PET scans were performed for the 4 patients: 2 baseline scans, 1 interim scan, 4 for end-of-treatment assessment, and 2 for post-treatment salvage assessment. SUV max values for lymphomatous lesions on PET scans ranged from 5.1 to 21.2. One patient was down-staged by baseline PET-CT. At the end of the treatment, all patients with PET-CT scans were evaluated. This resulted in four scans, two showing complete metabolic response and two showing progressive disease. Conclusion: Positron Emission Tomography – Computed Tomography (PET-CT) plays a crucial role in the intermediate evaluation of lymphomas, enabling better detection of residual or recurrent lesions, even where the distinction between active disease and post-therapy fibrosis is difficult. This contributes to a more accurate assessment of response to treatment, i.e., chemosensitivity. Furthermore, using PET-CT frequently provides better sensitivity than standard CT, leading to the detection of small or occult lesions. The study also highlights the importance of baseline PET scans in interpreting interim and post-therapy PET scans. Furthermore, continued characterization of the pathology, biology, and clinic of GZL is required, and new therapeutic regimens need to be investigated, including the integration of novel and rational therapeutic agents.