False-Positive Results and Incidental Findings with Annual CT or PET/CT Surveillance in Asymptomatic Patients with Resected Stage III Melanoma

Objective The aim of this study was to quantify false-positive and incidental findings from annual surveillance imaging in asymptomatic, American Joint Committee on Cancer stage III melanoma patients. Methods This was a cohort study of patients treated at Melanoma Institute Australia (2000–2015) with baseline computed tomography (CT) or positron emission tomography (PET)/CT imaging and at least two annual surveillance scans. False-positives were defined as findings suspicious for melanoma recurrence that were not melanoma, confirmed by histopathology, subsequent imaging, or clinical follow-up, while incidental findings were defined as non-melanoma-related findings requiring further action. Outcomes of incidental findings were classified as ‘benign’ if they resolved spontaneously or were not seriously harmful; ‘malignant’ if a second malignancy was identified; or ‘other’ if potentially harmful. Results Among 154 patients, 1022 scans were performed (154 baseline staging, 868 surveillance) during a median follow-up of 85 months (interquartile range 56–112); 57 patients (37%) developed a recurrence. For baseline and surveillance imaging, 124 false-positive results and incidental findings were identified in 81 patients (53%). The frequency of these findings was 5–14% per year, and an additional 181 tests, procedures, and referrals were initiated to investigate these findings. The diagnosis was benign in 109 findings of 124 findings (88%). Fifteen patients with a benign finding underwent an unnecessary invasive procedure. Surveillance imaging identified distant metastases in 20 patients (13%). Conclusion False-positive results and incidental findings occur in at least half of all patients undergoing annual surveillance imaging, and the additional healthcare use is substantial. These findings persist over time. Clinicians need to be aware of these risks and discuss them with patients, alongside the expected benefits of surveillance imaging.