Uptake Patterns of Untreated Primary Gastrointestinal Extranodal Lymphomas on Initial Staging 18F-FDG PET/CT and Metabolic Tumor Parameters

Non-Hodgkin’s lymphomas arising from tissues other than primary lymphatic sites are classified as primary extranodal lymphomas (PEL). PELs of the gastrointestinal system (PGISL) originate from the lymphatic tissues within the gastrointestinal tract. The prognostic value of 18F-FDG PET/CT in lymphomas is high in terms of both overall survival (OS) and disease-free survival (DFS). Our aim was to investigate the uptake patterns and properties of low-grade and high-grade PGISL on primary staging 18F-FDG PET/CT, as well as the prognostic significance of metabolic tumor parameters in high grade PGISL. Methods: Thirty-nine patients with PGISL were enrolled in this retrospective cohort study between 2004-2015. Primary staging 18F-FDG PET/CT have been performed and quantitative parameters of SUVmax, SUVmean, metabolic tumor volume (MTV), total lesion glycolysis (TLG) have been calculated for all patients prior to treatment. Low-grade and high-grade PGISL were compared in terms of metabolic tumor parameters. Cox regression models were performed to determine factors that correlate with DFS in high-grade PGISL.Results: There were statistically significant differences between high-grade and low-grade PGISL in terms of SUVmax, SUVmean, MTV, TLG, recurrence, mortality, DFS and OS. None of the potential risk factors (sex, age, site, SUVmax, SUVmean, MTV, TLG) for recurrence and metastasis in high grade PGISL was identified as a risk factor on univariate and multivariate Cox regression analysis. Conclusion: Metabolic tumor parameters are not predictive markers in high-grade PGISL, especially in diffuse large B cell variant and primary gastric lymphoma. The first implications suggest they will not play a role in patient management.