Impact of extranodal extension on risk stratification in papillary thyroid carcinoma.

BACKGROUND: The current American Thyroid Association (ATA) risk stratification system for papillary thyroid carcinoma (PTC) incorporates the number and size of positive lymph nodes (LNs), but places less weight on extranodal extension (ENE). We investigated how to incorporate ENE into the current system to predict recurrence better in PTC N1 patients.

METHODS: A total of 369 N1 PTC patients without distant metastasis were enrolled. We identified the combination of number of positive LNs and LNs with ENE that had the highest C-index in multivariable Cox proportional hazard models. ENE number was incorporated into the current system considering the recurrence rate and unadjusted and adjusted hazard ratios of subgroups. Kaplan-Meier curves for recurrence based on current and alternative systems were compared by log-rank test.

RESULTS: Recurrence rate for the subgroup with ≤5 positive LNs and 1-3 ENEs (7/61, 11.5%) was higher than that of the subgroup with ≤5 positive LNs without ENE [(5/129, 3.9%), adjusted HR 3.42 (0.99-11.75), P =0.050]. In contrast, adjusted HRs of the subgroup with >5 positive LNs and 1-3 ENEs [2.33 (0.52-10.35)] or with ≥4 ENEs [3.86 (1.05-14.17)] were not higher than those of subgroup with >5 LNs without ENE [4.47 (1.16-17.19)]. Incorporating ENE into the current system as an intermediate risk group yielded a lower log-rank P-value (0.05 vs. 0.01) than current system.

CONCLUSIONS: The presence of ENE in low volume LN metastasis confers an intermediate risk of recurrence. Incorporating ENE into the current system allows more accurate decisions regarding further management of PTC N1 patients. .