The significance of the presence of extranodal extension in the metastatic node of differentiated thyroid cancer: a proposal for modification in the American Thyroid Association (ATA) risk stratification

Multiple factors contribute to recurrences in differentiated thyroid cancers (DTC). Though the nodal size and number of positive nodes along with the presence of extranodal extension (ENE) have been mentioned in the present ATA risk stratification, the weightage given for ENE seems inadequate compared to the former two.

Factors predicting recurrences were analysed in this retrospective study of patients with DTC operated in a tertiary care centre. Based on our findings, we propose a modification in the present risk stratification. We have done so by comparing with existing risk stratification for fit and discrimination of this system.

Out of 1428 patients, 859 (60.2%) patients had pathological nodal metastases (pN +) with ENE being present in 26.8% of these. The recurrence rate was 6.4% (92 patients). Recurrence rates in patients with ≤ 5 nodes without ENE, > 5 nodes without ENE, ≤ 5 nodes with ENE and > 5 nodes with ENE were 2.7%, 1.3%, 8.3% and 10.3%, respectively. Recurrence rates in patients with 0.2–3 cm without ENE, 0.2–3 cm with ENE and > 3 cm with/without ENE were 1.8%, 8.5% and 13.4%, respectively. A modified risk stratification incorporating ENE and excluding the number of metastatic nodes was proposed. The modified risk stratification had a better fit than the present system in terms of higher C index and lower AIC.

Extranodal extension in differentiated thyroid cancer had the maximum influence on recurrence risk (recurrence-free survival) in our cohort. The prognostic impact of ENE supersedes the number of positive nodes in the risk of recurrence.