Is conservative treatment always safe in unifocal clinically T1a/node-negative papillary thyroid carcinoma?

Background: Management of clinically unifocal node-negative papillary thyroid carcinoma ≤1 cm (PTMC) is controversial with nonsurgical treatment as a potential alternative to thyroid lobectomy (TL). However, conservative strategies, such as active surveillance or thermal ablation, do not allow the evaluation of biological aggressive features or occult lymph node metastases (LNMs), which play a primary role as prognostic factors. Methods: Among 4216 thyroidectomies for malignancy (between September 2014 and September 2023), TL plus ipsilateral central neck dissection was performed in 203 (4.8%) unifocal N0 PTMCs. Completion thyroidectomy was accomplished in case of positive frozen section examination of removed nodes or within 6 months from index operation in presence of biological aggressive features. Results: Seventy-six out of 203 (37.4%) patients were staged pN1a and extranodal extension was detected in 5 (6.6%) patients. At final histology, biological aggressive features, including multifocality, lymphovascular invasion (LVI), extracapsular invasion, tumor aggressive subtypes, and BRAF-V600E mutation, were detected in 69 (34%), 93 (45.8%), 3 (1.5%), 30 (14.8%), and 7 (3.5%) patients, respectively. A comparative analysis between pN0 and pN1a patients showed younger age (p < 0.001), LVI (p = 0.037), and multifocality (p < 0.001) as risk factors for occult central LNMs. After logistic regression analysis, age (p < 0.001) and multifocality (p < 0.001) were confirmed as independent risk factors for nodal involvement. Conclusions: Although most PTMC has been widely defined as indolent disease, a non-negligible rate of patients may present one or more biologically aggressive features including nodal involvement. Nonsurgical management should be considered with caution to avoid undertreatment especially in the younger population.