FDG-PET predicts metastatic melanoma outcomes better than CT imaging
medwireNews: Using 18F-fluorodeoxyglucose–positron emission tomography (18F-FDG–PET) to measure immunotherapy response at 1 year in patients with metastatic melanoma may better predict long-term outcomes than standard computed tomography (CT), research shows.
With improved prediction of outcomes, PET may also “help guide discontinuation of therapy,” write Alexander Menzies (The University of Sydney, New South Wales, Australia) and colleagues in the Annals of Oncology.
The retrospective study included 104 patients (median age 65 years, 67% men) with metastatic melanoma who were treated with immunotherapy targeting programmed cell death protein 1 (PD-1) and underwent 18F-FDG–PET and CT imaging at the start of treatment and 1 year later.
According to RECIST criteria, 28% of patients had a complete response (CR) on CT imaging, 66% had a partial response (PR), and 6% had stable disease (SD) at the 1-year analysis.
By comparison, the complete metabolic response (CMR) rate, assessed using EORTC criteria for PET, was 75%, the partial metabolic response (PMR) rate was 16%, and the rate of stable or progressive metabolic disease (SMD/PMD) was 9%.
Of note, the majority (68%) of patients with a PR on CT imaging had a CMR when assessed by 18F-FDG–PET.
For patients with a CMR on 18F-FDG–PET but a PR or SD on CT, the most common residual sites on CT that were not avid on PET were the lung and lymph nodes.
After a median follow-up period of 30.1 months from treatment initiation, 102 (98%) patients were alive and 90 (87%) were progression-free.
Progression-free survival (PFS) at 1 year after repeat imaging was similar between patients with a CR and those with a PR or SD, with the median not reached in either group.
It was significantly better, however, in patients with a CMR, where the median was not reached, compared with a median of 12.8 months for those with no CMR. The proportions of patients who were progression-free at 1 year postimaging were 100% and 57%, respectively.
Similarly, median PFS was not reached for patients with a PR on CT and a CMR on 18F-FDG–PET, but it was 12.8 months in those with a PR but no CMR, a difference that was statistically significant.
The researchers point out that around a third of patients in both the CMR and non-CMR groups discontinued therapy within a year, but with better outcomes in the CMR group.
“Our results therefore suggest that as with the previous long-term analysis of the Keynote-001 trial that demonstrated cessation of therapy after CR on CT was safe, cessation of therapy after CMR on 18F-FDG PET may similarly be safe,” they remark.
Menzies and co-authors conclude: “Prospective evaluation of 18F-FDG PET scans is warranted,” adding that “the best timing of PET is yet to be determined.”
By Laura Cowen
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