A Disease Progression Predictor by Quantitative Assessment of the Hepatic Accumulation on Postablative Iodine-131 Whole-Body Image in Differentiated Thyroid Cancer.

Objectives: A Iodine-131 (¹³¹I) whole body scan (WBS) is performed to evaluate the treatment response after radioactive iodine (RAI) therapy. Despite the clinical relevance of RAI-refractory differentiated thyroid cancer, a consensus on its precise definition remains lacking. This study investigates the potential utility of hepatic ¹³¹I accumulation as an early predictor for tumor recurrence or progression after RAI administration.

Methods: Of 814 patients receiving care at our institution, we enrolled 225 patients who exhibited no accumulation of RAI in the remnant tissues or other lesions on ¹³¹I WBS. We quantified the hepatic uptake ratio [defined as (hepatic uptake/background uptake (H/B)] from WBS. All patients were categorized into group A (H/B ≤1.5) and group B (H/B >1.5), and we assessed between-group differences. The Kaplan-Meier method and Log-rank test were used to analyze the progression-free survival (PFS). Using the Cox proportional hazards model, we identified independent prognostic factors from among the seven known prognostic factors, i.e., H/B, thyroglobulin, sex, age, stage, total ¹³¹I dose, and final therapeutic dose.

Results: The 5-year and median PFS were 98.8% and 114.7 months in group A (n: 171) compared with 24.1% and 42.7% months in group B (n: 54), respectively. Group B showed a significant correlation with poor prognosis (p<0.00001). Of the seven prognostic factors, H/B exhibited the highest impact on patient outcomes (hazards ratio for recurrence/disease progression, 42.156; 95% confidence interval: 8.750-203.106).

Conclusion: Quantitative evaluation of hepatic uptake on ¹³¹I WBS provides a marker that may help identify patients with differentiated thyroid cancer who are at a high risk of disease progression/recurrence immediately after RAI therapy.