VI. FDG-PET as a biomarker in lymphoma: from qualitative to quantitative analysis.

Metabolic imaging with [18] Fluorine Fluorodeoxyglucosepositron emission tomography/computed tomography (FDG-PET/CT) provides a simple imaging biomarker capable to evaluate the glucose metabolism in fluorodeoxyglucose (FDG)-avid lymphoma tumours before treatment and for response assessment. Therefore, FDG-PET/CT has been very soon recognized as the more valuable imaging tool in FDG-avid lymphoma for response assessment by its property to image the residual metabolic activity irrespective of residual volume. The 2007 International Harmonized project criteria, the Deauvillle criteria in 2009, the Lugano classification and the recommendations of the International Conference on Malignant Lymphoma (ICML) imaging and clinical working groups in 2014 have set rules for harmonizing visual positron emission tomography (PET) reporting for response evaluation [1–4]. This was necessary for minimizing risk of reporting any residual uptake observed after treatment as an evidence of a residual tumour with resulting false positive studies. The interpretation key proposed by the ICML imaging group for both interim (iPET) and end of treatment PET (eotPET) is the Deauville 5-point scale (5P-S) using the classical visual assessment. However, it has been recommended by the group to investigate other quantitative approaches for response assessment. Similarly, ICML recommendations encourage investigating the quantitative analysis of FDG-PET/CT at staging. Indeed, new treatments have improved outcome in the most frequent types of lymphoma, but classic prognostic factors fail to select the small percentage of patients with high risk of relapse and treatment failure. For those reasons, we need new prognostic and predictive factors, a precise determination of initial tumour burden and an accurate and early assessment of responsiveness to therapy. FDG-PET/CT is by nature a quantitative imaging technique from which new metrics to measure tumour burden can be derived such as total metabolic tumour volume