Aim: To evaluate factors affecting ablation outcome in low- and intermediate-risk patients with differentiated thyroid cancer (DTC) as classified by the American Thyroid Association (ATA).
Methods: Patients with pathologically proven ATA low- or intermediate-risk-DTC were retrospectively recruited. Those with incomplete tumor-resection or distant metastases were excluded. Demographic and clinical data were collected from the patient's medical records. Prior to receiving I-131 ablation-therapy, each patient underwent a post-operative Tc99m-thyroid scan, baseline neck ultrasonography, baseline Tg level (BTG), and anti-Tg antibodies (Tg-Abs). Patients received variable doses of I131 ablation, post-therapy I-131 whole body scan (WBS) was then performed. Six months later, laboratory testing, neck-ultrasound and WBS were conducted to evaluate the ablation outcome. A successful ablation outcome is defined as undetectable stimulated thyroglobulin with negative Tg-Abs, free neck-ultrasound, and negative I-131-WBS.
Results: Two hundred and fifty patients, 128 low-and 122 intermediate-risk, were included. The successful ablation rate was 62.5% in low-risk, compared to 59% in intermediate-risk group. Patients with negative 99mTc-thyroid scans and absent thyroid-capsule infiltration in the low-risk group have significantly higher successful-ablation rates (76.7% vs. 55.3 %, p:0.01and 66.6 vs 62.5 %, p:0.03). In the intermediate-risk group, the successful-ablation rate in cases with low BTG was significantly higher than those with high BTG (67.7 % vs. 50%, P:0.04). Regression analysis revealed that negative thyroid scan and lower BTG are the significant predictor factors in low-risk patients (P: 0.03 and 0.04, respectively), while in intermediate-risk group, BTG was the only significant predictor factor (P: 0.007).
Conclusion: In ATA-low-risk DTC patients, an intact thyroid capsule, and a-negative 99mTc-thyroid scan were linked to a significantly higher successful-ablation outcome. Additionally, a negative thyroid scan and lower BTG were the significant predictor factors for successful-ablation outcome. BTG was the only significant predictive factor in the intermediate-risk group, and it was linked to a-higher successful-ablation rate.