Clinical outcomes of thermal ablation retreatment of benign thyroid nodules: A multicenter study from the Italian minimally-invasive treatments of the thyroid group

Unlabelled: Thermal ablation (TA) is an established therapeutic option alternative to surgery in patients with solid, benign thyroid nodules causing local symptoms. However, a variable part of thyroid nodules remain viable after these non-surgical treatments, and as many as 15% of nodules treated with TA may require a second treatment over time. This study aimed to evaluate the outcomes of TA retreatment on symptomatic benign thyroid nodules where the volume decreased by < 50% after the first procedure (=technique inefficacy). Methods: We performed a multicenter retrospective cohort study including patients that underwent retreatment with TA for benign thyroid nodules, whose volume decreased by < 50% after initial treatment. The primary aim was to evaluate volume and volume reduction ratio (VRR) over time and compare the 6- and 12-month VRR after first vs second treatment. The secondary aim was to identify protective or risk factors for technique inefficacy, regrowth and further treatments, expressed as adjusted hazard ratios (HRs) and 95% confidence interval (CI), after adjustment for sex, age, nodule volume, structure and function, nodule regrowth or symptom relapse, technique used and if the same technique was used for the first and second TA and time between them. Results: We included 135 patients. Retreatment led to VRR of 50% and 52.2% after 6 and 12 months. VRR after retreatment was greater than after first treatment in small and medium size nodules (<30 mL), while there were no differences for large nodules (>30 mL). After retreatment technique inefficacy rate was 51.9%, regrowth rate was 12.6%, and further treatment rate was 15.6%. Radiofrequency ablation (RFA) was protective towards technique inefficacy (HR 0.40; 95% CI: 0.24-0.65) and need of further treatments (HR 0.30; 95% CI: 0.12-0.76). Large nodule volume (>30 mL) was associated with increased risk of retreatment (HR 4.52; 95% CI: 1.38-14.82). Conclusion: This is the first study evaluating the outcomes of retreatment on symptomatic benign thyroid nodules with a VRR <50% after the initial TA treatment. Best results were seen in small and medium nodules (<30 mL) and after RFA. Prospective confirmatory studies are needed.