Is combining minimal extrathyroidal extension and size larger than 4 cm in T3 TNM stage for differentiated thyroid cancer appropriate - an analysis of sub-group specific recurrence risk.

Objectives: The T3 group of Differentiated Thyroid Cancer (DTC) represents an intermediate risk for recurrence and radioiodine ablation (RAI) is recommended (ATA guidelines). However, the of T3 group consist of two sub-groups: tumors over 4 cm (T3>4cm) and tumors with minimal extrathyroidal extension (T3mETE). There is little information comparing recurrence risk between those two sub-groups. Aim of this study is to evaluate if there is any difference in recurrence rate between T3>4cm and T3mETE in patients with T3 disease of DTC.

Methods: Patients were recruited from the London, Ontario, site of the Canadian Thyroid Cancer Consortium Registry (CTCCR). We identified patients with DTC T3 tumors who had at least 3 years of follow-up. We compared tumor characteristics, surgical management, number and doses of RAI and analyzed recurrence rates.

Results: We included 205 patients diagnosed between 1986-2013. There were 56 men and 149 women, with an average age of 50±15 years. 95 (46%) were included into T3>4cm group and 96 (47%) in T3mETE group. 14 (7%) met criteria for both groups and were excluded from further analysis. Treatment and follow-up duration were not different between groups; median follow-up was 6 (3-28) years. Recurrence occurred in 4 (5%) patients in the T3>4cm group and in 4 (5%) in the T3mETE group (P=NS).

Conclusion: The T3 sub-groups were fairly evenly distributed among the T3 stage. We did not find any difference in recurrence rate between T3>4cm and T3mETE subgroups. These results support the classification of both subgroups in the T3 group and the similar treatment recommendations in the ATA guidelines. Research Support: