Extrathyroidal Extension Is Associated with Compromised Survival in Patients with Thyroid Cancer

Background: Patients with thyroid cancer who have extrathyroidal extension (ETE) are considered to have more advanced tumors. However, data on the impact of ETE on patient outcomes remain limited. The purpose of this study was to evaluate the association between ETE and survival in patients with thyroid cancer. Methods: The National Cancer Database (1998-2012) was queried for all adult patients with differentiated thyroid cancer and medullary thyroid cancer. Patients were divided into three groups: no ETE (T1 and T2 tumors), minimal ETE (T3 tumors <4 cm), and extensive ETE (T4 tumors <4 cm). Patient demographic, clinical, and pathologic factors were evaluated for all patients. A Cox proportional hazards model was developed for each histology to identify factors associated with survival. Results: In total, 241,118 patients with differentiated thyroid cancer met the inclusion criteria; 86.9% had no ETE, 9.1% minimal ETE, and 4.0% extensive ETE. Compared with patients with no ETE, patients with minimal and extensive ETE were more likely to have larger tumors (1.4 cm vs. 1.8 cm and 2.0 cm, respectively), lymphovascular invasion (8.6% vs. 28.0% and 35.1%, respectively), positive margins after thyroidectomy (6.1% vs. 35.2% and 45.9%, respectively), and regional lymph node metastases (32.5% vs. 67.0% and 74.6%, respectively; all p < 0.01). After adjustment, minimal ETE (hazard ratio [HR] = 1.13; p < 0.01) and extensive ETE (HR = 1.74; p < 0.01) were associated with compromised survival for patients with differentiated thyroid cancer. In total, 3415 patients with medullary thyroid cancer met the inclusion criteria; 87.9% had no ETE, 7.1% minimal ETE, and 5.0% extensive ETE. Compared with patients with no ETE, patients with minimal and extensive ETE were more likely to have larger tumors (1.7 cm vs. 2.2 cm and 2.2 cm, respectively), lymphovascular invasion (19.2% vs. 68.9% and 79.3%, respectively), positive margins after thyroidectomy (5.8% vs. 44.1% and 51.9%, respectively), and regional lymph node metastases (39.0% vs. 90.5% and 94.4%, respectively; all p < 0.01). After adjustment, extensive ETE (HR = 1.63; p = 0.01) was associated with compromised survival for patients with medullary thyroid cancer. Conclusion: In patients with differentiated and medullary thyroid cancers, ETE is associated with compromised survival. Given these findings, ETE should be included in the thyroid cancer treatment guidelines.