Radiofrequency Ablation of Low-Risk Papillary Thyroid Microcarcinoma: A Retrospective Cohort Study Including Patients with More than 10 Years of Follow-up

Background: The longest reported follow-up for thermal ablation of papillary thyroid microcarcinoma (PTMC) is 5 years. We evaluated the long-term efficacy and safety of radiofrequency ablation (RFA) in patients with low-risk PTMC with clinical follow-up of more than 10 years. Methods: In this retrospective cohort study, we included patients with low-risk PTMC who had more than 10 years of follow-up after ultrasound (US)-guided RFA (performed between May 2008 and December 2013). Sixty-five consecutive patients with 71 low-risk PTMCs who were unsuitable for surgery or declined surgery were included. Before RFA, all patients underwent US and thyroid computerized tomography. Repeat RFA for staged ablation was performed when the first RFA did not secure sufficient safety margins because of the tumor closely abutting the recurrent laryngeal nerve. Follow-up US imaging was performed at 1 week, 3 months, 6 months, every 6 months until 2 years, and then annually afterward. Primary outcomes were the respective cumulative rates of disease progression (defined by local tumor progression, lymph node, or distant metastasis), newly developed thyroid cancer, and conversion surgery. Secondary outcomes were serial volume reduction rate (VRR), complete disappearance rate of ablated PTMC, and adverse events associated with procedures. Results: Of 65 patients included in the study, 60 had unifocal and 5 had multifocal PTMCs. The mean number of RFA sessions per tumor was 1.2, and the median follow-up duration was 151 months (interquartile ranges, 131-157). Twenty percent (13/65) of patients required repeat RFA. There were no cases of disease progression. Five patients (5/65, 7.7%) developed a new papillary thyroid cancer (four treated with RFA and one with lobectomy). At 24 months, the mean VRR was 100%, and this was maintained throughout the final follow-up. The complete tumor disappearance rates after one or more RFA treatments were 40.8% (29/71), 74.6% (53/71), and 100% (71/71) at 6, 12, and 24 months, respectively. One major (subclinical hypothyroidism) and three minor adverse events occurred. Conclusions: In our experience, RFA of low-risk PTMC is effective and safe. During more than 10 years of follow-up, we observed no incident local tumor progression nor metastases, but 7.7% of patients developed a new papillary thyroid cancer.