Interim PET-driven strategy in de novo diffuse large B-cell lymphoma: do we trust the driver?

F-18-Fluorodeoxyglucose-positron emission tomography (FDG-PET) has become a central tool for both accurate initial staging and determination of prognosis after treatment of diffuse large B-cell lymphoma (DLBCL). However, the role of PET during treatment (iPET) in daily practice remains a matter of significant debate. This perspective reviews the published studies on iPET in DLBCL, including the methods used to analyze iPET, its timing, and studies of iPET-driven therapy to illuminate where daily practice may benefit from the use of iPET. When performed after 2 and/or 4 courses of immunochemotherapy, iPET has a very good negative predictive value, utilizing both visual (qualitative) and semiquantitative methods. The visual method accurately predicts outcome for patients with limited disease. The semiquantitative method, eg, the change of the difference of maximum standardized uptake value (Delta SUVmax), is for patients with advanced DLBCL, for whom iPET identifies patients with very good outcome with continuation of standard therapy. A low Delta SUVmax also helps identify patients with a risk for relapse averaging 50% and warrants review of their scheduled therapy. To date, no trial has demonstrated the superiority of an iPET-driven strategy in DLBCL. However, the very good negative and good positive predictive values of iPET support its use in daily practice as a better predictive tool than contrast-enhanced computed tomographic scan for therapeutic decision making.