Patterns of metabolic response in patients receiving commercial CAR T-cells for relapsing/refractory aggressive B cells lymphoma

CAR T-cells is an innovative treatment for relapsed/refractory aggressive B cell lymphomas, initially proposed as third-line therapy and beyond, now allowed as soon as second-line treatment for patients with early relapse after first-line treatment. FDG PET/CT remains the modality of choice to evaluate response to this therapeutic strategy, to detect or confirm treatment failure, and allow for salvage therapy if needed. Correct classification of patients regarding response is thus of the utmost importance. In many cases, metabolic response follows classical known patterns, and Deauville score and Lugano criteria yield accurate characterization of patient status. However, given its specific mode of action, it can result in delayed response or atypical patterns of response. We report here a few examples of response from our experience to illustrate the existence of tricky cases. These atypical cases require multidisciplinary management, with clinical, biological, imaging, and pathological work-up.