Isthmic papillary thyroid microcarcinoma: clinicopathological features and prognostic factors following isthmusectomy...

This study aimed to compare clinicopathological features and recurrence risk in clinically node-negative (cN0) solitary isthmic papillary thyroid microcarcinoma (PTMC) ≤ 5 mm and > 5 mm in diameter treated with isthmusectomy, and to identify predictors of recurrence.

A retrospective review was performed of 201 cN0 patients with solitary isthmic PTMC who underwent isthmusectomy between 2018 and 2024. Patients with preoperative high-risk features were excluded. Subgroup analysis compared clinicopathological characteristics between the ≤ 5 mm (n = 107) and > 5 mm (n = 94) groups. Univariate and multivariate Cox models were used to identify factors associated with recurrence-free survival (RFS).

Significant differences were observed between the two groups in tumor size (p < 0.001), central lymph node metastasis (CLNM) (p = 0.009), microscopic extrathyroidal extension(mETE) (p < 0.001), and BRAF^V600E mutation (p = 0.008). During follow-up, 9 patients (4.5%) developed recurrence. Recurrence was significantly associated with tumor size > 5 mm (p = 0.028), CLNM (p = 0.002), and a higher number of metastatic central lymph node (CLN) (p < 0.001). Receiver operating characteristic analysis identified metastatic CLNs > 3 as the optimal cut-off for predicting recurrence. Kaplan-Meier analysis demonstrated worse RFS in patients with tumors > 5 mm (p = 0.031). Multivariate analysis confirmed metastatic CLNs > 3 as an independent predictor of recurrence (HR 5.298, 95% CI 1.473-19.060, p < 0.001).

This study demonstrated that isthmic PTMC tumors > 5 mm were associated with a higher risk of recurrence. In addition, CLNM, especially a metastatic CLNs > 3, may have prognostic significance and should be considered in surgical decision-making for isthmic PTMC.