US-guided Microwave Ablation of Low-Risk Papillary Thyroid Microcarcinoma: Longer-Term Results of a Prospective Study

Background: Papillary thyroid microcarcinoma (PTMC) has become a main cause of the extremely high incidence of thyroid carcinoma. This study aimed to evaluate the longer-term effectiveness of ultrasound (US)-guided microwave ablation (MWA) for treatment of low-risk PTMC with a large population. Methods: This prospective study was approved by ethics committee of our institution. MWA was performed under US-guidance for 119 unifocal PTMC patients without clinically cervical or distant metastasis. The target ablation zone exceeded the tumor edge judged by contrast-enhanced US to avoid marginal residue and recurrence. US and thyroid function evaluation were followed at 1, 3, 6, and 12 months after treatment and every 6 to 12 months thereafter. Any adverse event associated with MWA was evaluated. Results: The follow-up duration after MWA was 37.2 +/- 20.9 months (range 12-101 months). Tumor volume decreased significantly from 1.87 +/- 1.03 mL immediately after MWA to 0.01 +/- 0.04 mL at the final evaluation (P < 0.001), with a mean volume reduction ratio of 99.4 +/- 2.2% and 107 cases (93.9%) got complete remission. A patient was detected with cervical lymph node metastasis at 26-month follow-up and underwent 1 additional MWA treatment successfully. No distant metastasis was observed. All the acquired histological pathology results confirmed the absence of residual or recurrent tumor cells after MWA. No delayed complications associated with MWA were encountered for all patients. Conclusions: Percutaneous MWA is technically feasible for complete PTMC destruction and showed well longer-term effectiveness; thus, it seems to be an effective nonsurgical therapy to complement the current recommendation for selected low-risk PTMC patients.