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Surveillance imaging with FDG-PET in the follow-up of melanoma patients at high risk of relapse.
Background: In the modern era of melanoma treatment, approaches to imaging surveillance following surgery require reconsideration. The aim of this study was to evaluate disease sub-stage specific schedules of positron emission tomography (PET) surveillance for resected stage III melanoma. Methods: Between 2009-2013, patients at the Peter MacCallum Cancer Centre with fully resected AJCC stage III melanoma underwent serial whole body PET/CT scans according to schedules based on Bayesian disease sub-stage relapse probabilities. Schedules were stage IIIA: 6, 18 months; IIIB: 6, 12, 18, 24, 36, 48, 60 months; IIIC: 6, 12, 18, 24, 36 months. Descriptive statistics and contingency table analyses were used to evaluate outcomes for each schedule. Results: Eighty-six patients underwent PET surveillance according to schedule (IIIA: 11; IIIB: 50; IIIC: 25). In total, 232 PET scans were performed over a median follow-up of 28 months after surgery. Relapses were identified in 25 (29%) patients (IIIA: 4%; IIIB: 56%; IIIC: 40%), of which 20 (80%) were asymptomatic at the time of scanning. Incidental secondary malignancies were found in 6 (6.5%) patients. Stage IIIA/B relapses were more likely than stage IIIC to be loco-regional (IIIA/B: 42%; IIIC: 10%; p = NS). Nine (36%) relapsed patients underwent potentially curative resection (IIIA: 1; IIIB: 6; IIIC: 2), with 5 (IIIA: 1; IIIB: 4) free of disease after a median 32 months follow-up. The positive and negative predictive values (PPV, NPV) of an individual PET scan for detecting disease relapse at the same time point were: stage IIIB – PPV 69% (CI: 43-87%) and NPV 99% (CI: 95-100%), stage IIIC – PPV 73% (CI: 39-94%) and NPV 97% (CI: 90-100%). The PPV and NPV of each surveillance protocol for detecting any disease relapse were: stage IIIB – PPV 68% (CI: 43-87%) and NPV 97% (CI: 83-99%), stage IIIC – PPV 73% (CI: 39-94%) and NPV 86% (CI: 57-98%). The sensitivity and specificity of the overall approach of sub-stage specific PET/CT surveillance for detecting disease relapse were 88% (CI: 69-97%) and 84% (CI: 72-92%), respectively. Conclusions: FDG-PET is effective in detecting asymptomatic metastases and thus facilitating early treatment in patients who relapse after resection of stage III melanoma.