Abstract
BACKGROUND: Thermal ablation (TA) of papillary thyroid carcinoma (PTC) has been reported to have promising results. However, performing microwave ablation (MWA) on PTCs located in the isthmus remains controversial. OBJECTIVES: This study aimed to compare the feasibility, effectiveness, and safety of MWA for treating PTC in the isthmus and lateral lobes. DESIGN: Prospective cohort study. METHODS: In this study, between December 2019 and December 2020, patients with clinical T1N0M0 PTC who planned to receive MWA were enrolled from 12 hospitals. All tumors were evaluated by preoperative ultrasound and divided into isthmus-located tumors and lobe-located tumors. The patients were followed until 1 February 2025. The primary endpoints included technical success and disease-free survival. The secondary endpoints included treatment parameters, complications, and tumor shrinkage. Variables were compared between the two groups, and subgroup analysis was performed. RESULTS: After exclusion, 652 patients (mean age, 43 years ± 11 (SD), 481 females) were included: 109 with PTC in the isthmus and 543 with PTC in the lateral lobes. One isthmic tumor terminated MWA, 108 versus 543 (mean tumor volume of 0.1 ml ± 0.1 vs 0.2 ml ± 0.2, p = 0.14), was analyzed, with a mean follow-up period of 61 months ± 5 (range, 54-67 months). Comparable technical success rates were achieved (99% (108/109) versus 100% (543/543), p = 0.17) for isthmic tumors and lobe tumors, with 1 versus 24 complications (0.9% (1/108) vs 4.4% (24/543), p = 0.08). Although fewer isthmic tumors achieved the targeted safety margin (2 mm) than did lobe tumors (50.0% (54/108) vs 61.0% (331/543), p = 0.03), no differences in disease-free survival (97.2% (105/108) vs 97.4% (529/543), p = 0.91) or tumor shrinkage (96 ± 16% (SD) vs 95 ± 17% (SD), p = 0.70) were detected. In the tumor stage, capsular invasion, safety margin, sex, age, and thyroid disease subgroups, the outcomes remained comparable. CONCLUSION: MWA was feasible for T1N0M0 PTC in the isthmus and showed comparable efficacy in comparison with tumors in the lobes. TRIAL REGISTRATION: NCT04197960.