Risk Factors for Indeterminate Response After Radioactive Iodine Therapy in Patients With Differentiated Thyroid Cancer

Abstract

PURPOSE: We investigated the risk factors of indeterminate response (IDR) in patients who underwent recombinant human thyroid-stimulating hormone (rhTSH)-aided radioactive iodine therapy (RAIT). METHODS: A total of 128 patients with papillary thyroid cancer were included in this retrospective study. The patients were classified into excellent response and IDR groups based on follow-up diagnostic whole-body scintigraphy (WBS) and TSH-stimulated thyroglobulin (Tg). Indeterminate response was defined as the presence of a faint uptake in the thyroid bed on the diagnostic WBS or a TSH-stimulated Tg detectable, but less than 10 ng/mL. Parameters that act as significant risk factors for IDR, including age, sex, stage, surgeon, time interval between surgery and RAIT, post-treatment WBS finding, urine iodine-to-creatinine ratio, TSH-unstimulated Tg, and rhTSH-stimulated Tg, were analyzed using a Cox proportional hazards regression method. RESULTS: After treatment, 64 patients showed IDR. Recombinant human TSH-stimulated Tg was the only independent risk factor for predicting IDR. Patients with an rhTSH-stimulated Tg greater than 2 ng/mL prior to RAIT were 3.75 times more likely (95% confidence interval, 1.61-8.72) to have an IDR than those with a lower rhTSH-stimulated Tg (</=2 ng/mL). CONCLUSIONS: Pre-RAIT TSH-stimulated Tg levels are a risk factor for IDR after RAIT.