Patients with high‐risk differentiated thyroid cancer have a lower I‐131 ablation success rate than low‐risk ones in spite of a high ablation activity. (29th June 2016) - Winter, J.
Summary: Objective: To examine success rates in strictly defined high‐risk differentiated thyroid cancer (DTC) patients who received a high‐activity (≥5550 MBq) adjuvant postoperative I‐131 therapy and compare these to the rates found in highest risk and low‐risk patients. Design: Retrospective database study. Patients: We examined 377 patients with DTC who received I‐131 ablation. Patients with distant metastases were classified as very high risk. Patients with primary tumours >4 cm, extensive extrathyroidal invasion (pT4a or pT4b in accordance with the 7th edition of the TNM system), and patients with ≥5 lymph node metastases or any lateral compartment lymph node metastases were considered high risk. All other patients were considered low risk. Measurements: Ablation success rate at first TSH‐stimulated follow‐up. Results: The ablation success rate was 72·6% in low‐risk patients, 51·7% in high‐risk patients and 13·8% in highest risk patients (all differences P < 0·001). In none of the groups, a significant difference in the initial I‐131 activity was found between patients with successful and unsuccessful ablation (low risk: P = 0·16, high risk: P = 0·91 and highest risk: P = 0·48). Furthermore, there was no difference in ablation success between patients who received <5550 MBq and those who received ≥5550 Mbq (low risk: P = 0·31, high risk: P = 0·69 and highest risk: P = 0·22). Conclusions: Patients with high‐risk DTC have a significantly reduced I‐131 ablation success rate compared to low‐risk ones in spite of high initial I‐131 activities. As successful ablation is prognostically important, efforts should be made to improve outcome in these patients.