Abstract
1347
Objectives: Nivolumab is an immune checkpoint inhibitor that targets programmed death-1 (PD-1) and re-activates the immune system to fight cancer cells. FDG-PET has been utilized for monitoring the effects of treatment in cancers but the role of this imaging modality in the assessment of response to nivolumab is still being investigated. Our goal was to evaluate the metabolic response to this treatment in NSCLC patients by adopting novel quantitative FDG-PET techniques that allows measuring global disease activity.
Methods: We reviewed the FDG PET imaging data from 16 patients with NSCLC who received nivolumab. A total of 72 whole body FDG-PET scans including: two scans before starting treatment and two scans following treatment were evaluated. Additionally, 8 subjects had a mid-treatment scan that was also included in this analysis. The images were analyzed using an adaptive thresholding system (ROVER software; ABX GmbH, Radeberg, Germany). All active lesions including those in the lungs, lymph nodes and distant sites were analyzed. The partial volume corrected total lesion glycolysis (pvc TLG) was measured by multiplying the total active lesion volume as determined by this software and pvc SUVmean of the lesions. The PET scan before the initiation of nivolumab was considered as the baseline scan and the pvc TLGs of different time-points were normalized by dividing each value by that of the baseline scan. Linear graphs were plotted to demonstrate the changes of normalized pvc TLG during the course of the treatment. Furthermore, percent changes between the baseline scan, mid-treatment and the first post treatment scan were calculated (Δpvc TLG).
Results: The pvc TLG in all 8 subjects (100%) who had a mid-treatment scan had a decrease compared to the baseline scan (average Δpvc TLG = -68%). Among the 16 subjects, only one subject (6%) had a complete response to nivolumab after finishing the treatment. Seven patients (43%) had a partial response to nivolumab by a mean drop of 60%. Progression on FDG was observed in eight patients (50%) with the mean increase in pvc TLG by +377%.
Conclusions: Global disease assessment with FDG-PET is a powerful quantitative technique to assess treatment response and evaluate disease progression in NSCLC patients receiving nivolumab. Quantitative response assessment provides a clear metric for evaluating the course of the patients’ disease, and may provide ordering physicians more meaningful data for clinical decision-making as compared with the existing qualitative measures of response. In addition, it provides a simple metric that allows for automated testing of hypotheses related to patterns of treatment response in patient’s receiving immunotherapy.