Extranodal Extension May Indicate Intermediate Recurrence Risk in Papillary Thyroid Carcinoma

The presence of extranodal extension indicates an intermediate risk for recurrence in papillary thyroid carcinoma (PTC), according to study results published in Thyroid. The findings underscore the value of including extranodal extension in the current system of managing PTC with lymph node metastasis.

This retrospective single-center study included 369 individuals with PTC and no distant metastasis, all of whom were ≥18 years old (median age, 42 years; 63% women). Central compartment node dissection was performed on all participants with or without lateral compartment node dissection, and both selective and prophylactic central neck dissection were performed in accordance with American Thyroid Association (ATA) guidelines.

Cox proportional hazard models were used to assess the associations between recurrence and combinations of positive lymph nodes/number of extranodal extensions. The researchers then incorporated the rate of recurrence and hazard ratios calculated in the statistical models into the current ATA risk stratification system for PTC.

As expected, a close association was found between the number of positive lymph nodes and extranodal extensions, with a Pearson’s correlation coefficient of 0.66 (P <.001). In the subgroup with ≤5 positive lymph nodes and 1 to 3 extranodal extensions, risk for recurrence was significantly higher compared with patients who had ≤5 positive lymph nodes and no extranodal extensions (adjusted hazard ratio, 3.42; 95% CI, 0.99-11.75; P =.050), with recurrence rates of 11.5% vs 3.9%, respectively.

Recurrence was not significantly higher in subgroups with >5 positive lymph nodes and 1 to 3 extranodal extensions or ≥4 extranodal extensions compared with patients in the subgroup who had >5 positive lymph nodes and no extranodal extensions (adjusted hazard ratio, 2.33 [95% CI, 0.52-10.35] vs 3.86 [95% CI, 1.05-14.17] vs 4.47 [95% CI, 1.16-17.19]).

When the investigators included extranodal extension in the ATA’s current PTC risk stratification system, 32.8% of patients originally categorized as low risk with ≤5 positive lymph nodes were increased to intermediate risk. The Kaplan-Meier curve for recurrence of the researchers’ proposed system was compared with that of the ATA’s risk system using a log-rank test; the new system accounting for extranodal extension had a significant log-rank P value of 0.010, while the current ATA system did not (P =.050).

Limitations to this study include its short duration and potential lack of applicability to long-term prognosis, a small sample size for certain subgroups, its retrospective design, and the potential for recurrent disease as a result of incomplete lymph node dissection.

“After incorporating [extranodal extension] into the current risk stratification system to create an alternative system, this system showed a better predictive ability than the current ATA risk-stratification system for predicting structural persistent/recurrent disease,” wrote the researchers. “The present results are useful when determining the initial treatment after surgery.”

Reference

Kim HI, Hyeon J, Park SY, et al. Impact of extranodal extension on risk stratification in papillary thyroid carcinoma [published online May 30, 2019]. Thyroid. doi:10.1089/thy.2018.0541