Endocrine Abstracts

Introduction: Patients diagnosed with DTC have excellent prognosis. A small percentage of patients with disease persistence do not respond to treatment with RAI (RAI-refractory DTC) and have low median survival (3.5 years). We investigated the prognostic factors and the disease course in patients with RAI-refractory DTC.

Methods: Of all DTC patients (n=1160) followed-up in our department in recent years, 800 received RAI treatment and were classified in 2 groups: RAI-refractory DTC (5.8%) and RAI responsive DTC (94.2%). Clinical and histological characteristics were compared between the 2 groups.

Results: The incidence of RAI-refractory DTC was higher in patients ≥45yrs and particularly in those ≥65yrs (3% vs 7.4% vs 17.4%, P=0.001). Men had RAI-refractory DTC more frequently than women (P=0.02). RAI-refractory DTC patients presented higher incidence of capsular, lymph node and extra-thyroid invasion (P<0.004), larger size (P<0.001), worse histological type (high risk papillary: 34.9% vs 12% and features of poor differentiation: 14%vs0.6% respectively, P<0.001,). They presented more frequently distant metastases at follow-up (73.3% vs 1.5%, P<0.001). 12 RAI-refractory patients had local persistence. 5/12 had no distant metastasis; all underwent multiple surgeries and 3 locoregional external radiation therapy. The 10-year probability of lack of progression of disease was 27.9% vs 98.8% (x²=297, P<0.001). In Cox proportional hazard analysis, the only predictor for disease progression was resistance to RAI (HR 0.032, 95% CI 0.007–0.146, P<0.001). Within the RAI-refractory DTC subgroup, when age at diagnosis, gender, tumor size, histological type, lymph node, capsular and tissue invasion were taken into account, the only predictor for disease progression and occurrence of distant metastases was tumor size (P=0.008 and P=0.015 respectively).

Conclusions: Patients with RAI-refractory DTC present disease progression at high percentage (72.7%). In these patients, tumor size is the most important unfavorable factor predicting disease progression and occurrence of distant metastases. These data may be useful in designing treatment strategy.