Incidentally detected 18F-FDG PET-CT-avid thyroid nodules in patients with advanced malignancy: long-term oncological outcomes from a single-centre retrospective cohort.

Thyroid nodules are frequently detected incidentally on 18F-fluorodeoxyglucose PET-computed tomography (18F-FDG PET-CT) studies and may prompt, further, often invasive investigation for malignancy. Published malignancy rates in thyroid nodules incidentally detected on 18F-FDG PET-CT range from 15 to 80%. The vast majority of these nodules are clinically nonsignificant, well differentiated microcarcinomas with no impact on morbidity or mortality. This is a very important consideration in patients with established non-thyroidal malignancies. In this retrospective study, we evaluate the clinical outcomes in patients undergoing 18F-FDG PET-CT for their principal malignancy. From 162 incidental thyroid nodules, 50 were investigated with ultrasound. Of these, 37 patients underwent fine needle aspiration (FNA) (average of 1.3 FNA attempts) with a total of six patients having incidental thyroid cancer. All were indolent papillary cancers without any impact on treatment or survival. Our study demonstrates that the clinical outcomes of patients with an established primary malignancy are determined by their primary cancer and not by incidentallydetected thyroid cancer. Therefore, a watch-and-wait approach may be considered more appropriate in such patients.