Impact of perinodal infiltration on recurrence in papillary thyroid cancer.

Introduction and objectives: Locoregional recurrence occurs in up to 28% of patients with papillary thyroid cancer (PTC). Several risk factors contribute to this metastatic process. The latest of them is perinodal infiltration (PNI). PNI refers to the pathological extension of tumor cells through the lymph node (LN) capsule into the perinodal fibroadipose tissue. It has been accepted as a poor predictive variable. This study aimed to evaluate the prognostic significance of PNI in recurrence of PTC and identify predictive parameters associated with the recurrence in PNI (+) patients.

Material and methods: The study included 680 PTC patients with initial LN metastasis (ILNM). Study population was selected from them according to presence or absence of PNI. Eventually, 102 PNI (+) and 122 PNI (-) patients remained eligible for the study. Patients were statistically compared according to demographic, clinicopathologic features both between PNI (+) and PNI (-) groups and within the PNI (+) group over recurrence status.

Results: The recurrence rates were 40% and 15% in PNI (+) and PNI (-) patients, respectively (p < 0.001). The independent predictive factors associated with recurrence were central ILNM (p = 0.005), combined central and lateral ILNM (p = 0.003), ILNM > 5 (p = 0.023), stage III-IV (p = 0.025 and p < 0.001), tumor size (TS) (p < 0.001), ILNM size (p < 0.001), stimulated thyroglobulin (sTg) (p = 0.039). PNI (p = 0.05), central ILNM (p = 0.035) and TS (p = 0.027) remained prognostic variables after multivariate analysis.

Conclusion: PNI positivity is a poor prognostic factor for PTC recurrence. PNI, especially with large TS and central ILNM, should be taken into account when planning RAI therapy in PTC patients.