Residual FDG‐PET metabolic activity in metastatic melanoma patients with prolonged response to anti‐PD‐1 therapy

Abstract

18-Fluorodeoxyglucose positron emission tomography (FDG-PET) scans were performed on 27 patients with unresectable stage IIIC or IV melanoma after prolonged treatment with anti-PD-1 antibodies to examine the hypothesis that patients with prolonged response to treatment may have metabolically inactive lesions by FDG-PET. Scans were performed at a median of 15.2 months (range 12-29 months) after starting treatment. Overall, 15 of 27 (56%) patients had a positive FDG-PET scan. Eight patients with positive scans underwent biopsy; 5 of 8 (62%) were melanoma and 3 of 8 (38%) were immune cell infiltrates. Of the 12 patients with negative FDG-PET scans, six had residual computerized tomography-visible lesions, five have ceased treatment, and none have recurred with follow-up of 6-10 months. Patients with residual metastases after a prolonged period without progression on anti-PD-1 therapy may have metabolically inactive lesions. Isolated metabolically active lesions in clinically well patients may reveal immune cell infiltrates rather than melanoma.

In Vivo Molecular Imaging for Biomedical Analysis and Therapies

“…42,43 However, since [ 18 F]FDG accumulates in the immune activated region, it may not be easy to predict the therapeutic effect in some patients. 44 In some cases, a combination of several imaging agents might be effective for prediction and monitoring the therapies.…”

Nuclear Molecular Imaging Strategies in Immune Checkpoint Inhibitor Therapy

“…Two patients were initially classified as having stable metabolic disease (SMD), while the late scan (after four cycles) showed progressive metabolic disease (PMD), and two patients, who ended up having partial metabolic response (PMR) on the late scan, were originally wrongly classified as having PMD on the early scan [32]. Similarly, a study from Australia in 27 melanoma patients undergoing prolonged treatment with a PD-1 inhibitor found that, amongst those with residual disease on CT, 43% had negative FDG PET scans and that none of the patients with negative FDG PET scans progressed within the 6–10 months follow-up period [33]. …”

The new era of cancer immunotherapy: what can molecular imaging do to help?

“…Only very limited data are available for the evaluation of immunotherapy by means of 18 F-FDG-PET. Two clinical experiences have been made in 49 patients [6, 7], demonstrating the inability of 18 F-FDG PET/CT make a differential diagnosis between patients with pseudo-progression (due to inflammatory infiltrate) from those with a real progression, during immunotherapy. In fact, it has been reported that the initial increase in tumor size, later followed by tumor volume reduction in part of the patients treated with immune checkpoint inhibitors, is due to inflammatory cell infiltrates [2, 6, 7].…”