Aggressive Subtypes of Papillary Thyroid Carcinoma Smaller Than 1 cm

CONTEXT: Tumor size is important in determining the range of surgery in papillary thyroid carcinomas (PTCs), especially those smaller than 1 cm. OBJECTIVE: We aimed to analyze the features of small PTCs with aggressive subtypes based on histological characteristics. METHODS: In this retrospective study, we reviewed the medical records of 11 570 patients with PTCs smaller than or equal to 1 cm who underwent thyroidectomy between January 2009 and December 2016. Aggressive subtypes included diffuse sclerosing, solid, tall cell, columnar cell, and hobnail subtypes. RESULTS: Among the 11 570 patients with PTCs smaller than or equal to 1 cm, 177 aggressive PTC subtypes were identified. Propensity score matching revealed 110 tumors (62.1%) with extrathyroidal extension of aggressive PTC subtypes and 451 (51.1%) nonaggressive PTC subtypes (95% CI, 0.41-0.80; P < .001). Metastatic central and lateral neck lymph nodes constituted 3.06 ± 3.67 and 3.81 ± 5.39 of aggressive PTC subtypes and 1.22 ± 2.14 and 2.85 ± 3.79 of nonaggressive PTC subtypes, respectively (central neck nodes: 95% CI, 1.42-2.26; P < .001; lateral neck nodes: 95% CI, 2.9-5.90; P < .001). Seven patients with aggressive PTC subtypes (3.95%) and 12 with nonaggressive PTC subtypes (1.7%) exhibited recurrence. CONCLUSION: Aggressive subtypes of small PTC tumors smaller than or equal to 1 cm exhibited more extrathyroidal extension and neck node metastasis. This study suggests that surgeons should consider the aggressive subtypes as important factors when deciding the range of surgery in PTCs smaller than 1 cm.