Retrospective analyses of 18FDG-PET/CT thyroid incidentaloma in adults: incidence, treatment and outcome in a tertiary cancer referral center.

Introduction A thyroid incidentaloma (TI) is an unexpected, asymptomatic thyroid lesion discovered during the investigation of an unrelated condition. The aim of the present study is to examine the incidence of 18FDG-PET TI, the associated management strategies and the outcomes in a tertiary cancer referral center over the last 10 years. Methods This study involves a retrospective cohort study of 1003 patients with TI depicted on 18FDG-PET/CT scans performed between January 2010 and January 2020 for a non-thyroid cancer. The Kaplan-Meier method was used for survival analyses in patients concerning an underlying malignancy with a prevalence of 5% or higher in this cohort. Logistic- and cox regression analyses were performed to analyze predictors of thyroid malignancy and mortality. A propensity score weighted method was used to control for baseline differences between the intervention (additional TI diagnostics) and control (no TI diagnostics) group. Results FDG-positive TI occurred in 1.9% (1003/52693) of the oncologic 18FDG-PET/CT scans performed in our center. Thyroid sugery was performed in 47 patients (6%) and a thyroid malignancy was detected in 31 of them, which is 66% of the operated group and 4% of all patients. During the follow-up (median 6 years), 334 deaths (42%) related to different types of cancer (38%) or other causes (4%) were observed. One patient died from medullary thyroid cancer. Age, gender, the type- and American Joint Committee on Cancer stage of non-thyroid cancer were statistically significant predictors of patient survival in multivariate analysis. Conclusion The incidence of TI in this tertiary cancer referral center was comparable to current literature. Further thyroid work-up was performed in less than half of the patients and only a minority of patients underwent thyroid surgery. Since only one patient died from thyroid cancer, the strategy to withhold from thyroid diagnostics and treatment seems valid for most TI. Active thyroid treatment might benefit a subgroup of patients in whom the non-thyroid primary cancer is successfully treated or presumably stable. A wait-and-see policy with ultrasound follow-up could be an alternative strategy. These considerations should be part of the shared decision making in cancer patients with a TI.