Perineural Invasion Is Not an Independent Risk Factor for Recurrence and Lateral Neck Metastasis in Thyroid Cancer: A Propensity Score Matching Analysis.

Objectives: Perineural invasion (PNI) in thyroid cancer is a relatively rare but significant pathologic feature with crucial implications for prognosis and management. This study investigates the impact of PNI on recurrence and lateral neck lymph node metastasis (N1b) in patients with thyroid cancer.

Methods: This retrospective analysis included 8572 patients with thyroid cancer who underwent surgery from January 2000 to December 2020 at Seoul St. Mary's Hospital. Clinicopathologic characteristics and outcomes were compared between the patients with and without PNI before and after propensity score matching (PSM). The logistic regression analysis identified the risk factors for N1b, whereas the Cox regression analysis determined the risk factors for recurrence.

Results: Of the 8572 patients, 144 (1.7%) presented with PNI. The PNI group had higher rates of gross extrathyroidal extension, vascular and lymphatic invasion, and advanced TNM stage. The recurrence rates were higher in the PNI group both before (11.1% vs 5.6%) and after PSM (11.3% vs 5.6%). PNI was a significant risk factor for N1b in the univariate logistic regression analysis but not in the multivariate analysis before and after PSM. The Cox regression analysis revealed that PNI is a significant risk factor for recurrence before PSM but not after PSM.

Conclusions: The PNI in thyroid cancer was associated with higher recurrence rates and increased N1b. However, it was not considered a significant independent risk factor for recurrence or N1b. Further research is needed to refine the management strategies for patients with PNI to improve prognosis.