Abstract 3034: 18F-FDG-positron emission tomography (PET)/CT enables the identification of checkpoint inhibitor immunotherapy (CIT) responders by determination of CIT-induced metabolic changes in secondary lymphatic organs

Although the majority of patients with metastatic melanoma achieve a prolongation of overall survival by using checkpoint inhibitor based immunotherapy (CIT), there is still a larger number of patients who do not benefit from this therapy. As a CIT-induced systemic immune response is required to promote the anti-tumor effect we analyzed the glucose metabolism in secondary lymphoid organs such as the spleen by 18F-FDG-Positron Emission Tomography (PET). In preclinical studies, we were able to distinguish responders from non responders by focusing on the spleen 18F-FDG-uptake of mice with CIT in experimental tumor models. Thus, we aimed to gain deeper insights into impact of CIT on the metabolism in secondary lymphatic organs to identify responders and to stratify patients for differential treatment strategies. We retrospectively analyzed 18F-FDG-PET/CT scans (baseline and post-therapy) of 38 patients with metastatic melanoma with CTLA-4 or PD-1 Ab treatment as third line therapy (21 responder: 5x nivolumab; 7x pembrolizumab; 9x ipilimumab; 17 non-responder: 2x nivolumab; 11x pembrolizumab; 4x ipilimumab). Spleen regions of interest (ROI) were defined in the CT data, copied to the coregistered PET and analyzed semiquantitatively. Total lesion glycolysis (TLG) was calculated by multiplication of the spleen volume and the SUVmean. We determined in the baseline 18F-FDG-PET/CT-scans (prior to CIT), no significant differences in spleen volume (221±18 cm3 vs. 209 ±22 cm3) and in the spleen 18F-FDG-uptake (SUVmean: 1,74±0,06vs.1,72±0,05; TLG: 384±37 vs. 359±36) between responders and non-responders. In the follow up 18F-FDG-PET/CT-scans 110±68 days after onset of CIT we measured a similar increase in spleen volume in responders (+8±6%) and non-responders (+7±5%). 15 out of 21 responders revealed an enhanced spleen 18F-FDG uptake when compared to the baseline 18F-FDG-PET/CT-scans. The mean standard uptake values in the spleen of responders increased by +10±9% SUVmean. In sharp contrast, we determined hardly any change in the spleen 18F-FDG uptake of non-responders (SUVmean -1,3±2,6%). Additionally, the total lesion glycolysis (TLG) in the CIT-responders increased stronger (+25±22%) than in non-responders (+6±6%). Our results suggest that CIT-induced metabolic changes in secondary lymphatic organs are associated with therapy responds. Thus, non invasive 18F-FDG-PET/CT investigations might represent a powerful tool to monitor CIT-induced systemic immune responses in patients. Consequently, preclinical research is prerequisite to uncover the exact mode of action of CIT-induced systemic immune response in secondary lymphatic organs. Moreover, prospective clinical studies are essential to evaluate the prognostic value of our method. Citation Format: Johannes Schwenck, Barbara Schörg, Francesco Fiz, Kilian Wistuba-Hamprecht, Andrea Forschner, Thomas Eigentler, Benjamin Weide, Claus Garbe, Martin Röcken, Christina Pfannenberg, Bernd J. Pichler, Christian la Fougere, Manfred Kneilling. 18F-FDG-positron emission tomography (PET)/CT enables the identification of checkpoint inhibitor immunotherapy (CIT) responders by determination of CIT-induced metabolic changes in secondary lymphatic organs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3034.