Characteristics and risk factors analysis of patients with cN1b papillary thyroid microcarcinoma: a retrospective single-center study.

[BACKGROUND] Lateral lymph node metastasis (LLNM) increase the risk of local recurrence and secondary surgery, posing a significant physical, psychological and economic burden on patients with papillary thyroid microcarcinoma (PTMC). Therefore, it is necessary to analyze the clinicopathological features and risk factors of recurrence in these cN1b PTMC patients,thereby guiding risk-stratified clinical management.

[METHODS] A retrospective cohort of 246 patients with cN1b PTMC who underwent primary surgery at Zhejiang Cancer Hospital (January 2008-December 2017) was analyzed. Clinicopathological data and long-term follow-up outcomes were collected. Univariate and multivariate logistic regression analyses were used to identify predictors of skip lateral lymph node metastasis (SLNM) and recurrence, while Kaplan-Meier survival analysis with log-rank tests was used to compare recurrence-free survival between subgroups.Sample size calculation was performed to ensure statistical power, and temporal stratification was used to mitigate retrospective bias.

[RESULTS] Multivariate logistic regression identified two independent predictors of SLNM: maximum tumor diameter ≤ 5 mm (OR = 2.84) and absence of intrathyroidal dissemination (OR = 16.19). Notably, SLNM was not associated with recurrence or disease-specific survival (DSS). During follow-up, 14 patients had lymph node recurrence and 6 patients had local recurrence, 2 patients died of thyroid cancer. Multivariate analysis confirmed three independent recurrence predictors: extrathyroidal extension (ETE, OR = 4.06, 95% CI 1.14-14.38), upper-pole tumor location (OR = 3.58, 95% CI 1.34-9.58), and intrathyroidal dissemination (OR = 2.88, 95% CI 1.14-7.28). Kaplan-Meier analysis showed significantly higher recurrence rates in patients with ETE (21.9% vs. 6.1%, P < 0.05), upper-pole tumors (13.8% vs. 4.6%, P < 0.05), and intrathyroidal dissemination (18.4% vs. 6.3%, P < 0.05).

[CONCLUSION] In cN1b PTMC, SLNM is independently associated with tumor size ≤ 5 mm and absence of intrathyroidal dissemination but not with recurrence or DSS, suggesting it should be a key target for preoperative imaging evaluation rather than a poor prognostic factor. ETE is one of the most important independent recurrence risk factors, alongside upper-pole location and intrathyroidal dissemination-its effect magnitude requires cautious interpretation due to a wide confidence interval. A risk-stratified strategy is supported: patients with these high-risk features may consider more radical treatment and intensified postoperative surveillance. This study provides evidence-based guidance to improve disease-free survival in cN1b PTMC patients.