Delayed initial radioiodine therapy related to incomplete response in low- to intermediate-risk differentiated thyroid cancer

OBJECTIVE: Whether the initiating time of radioiodine (RAI) therapy will affect the clinical outcome in differentiated thyroid cancer (DTC) remains controversial. The objective of this study was to evaluate the impact of RAI therapy initiating time on response to initial therapy in low- to intermediate-risk DTC. METHODS: A total of 235 consecutive patients with low- to intermediate-risk DTC were retrospectively reviewed. According to the time interval between thyroidectomy and RAI therapy, patients were divided into Group 1 (interval < 3 months, n = 187) and Group 2 (interval ≥ 3 months, n = 48). Response to RAI therapy was evaluated as excellent, indeterminate, biochemical incomplete or structural incomplete response (ER, IDR, BIR or SIR) with a median follow-up of 780 days. The univariate and multivariate analyses were further conducted to identify factors associated with incomplete response (IR, including BIR and SIR). RESULTS: Response to initial therapy was significantly different between 2 groups (P < .05), after excluding the impact of other risk factors (age, gender, histological type, status of T and N, RAI dose, thyrotropin, stimulated thyroglobulin and follow-up time). A significantly higher IR rate (18.8% vs 4.3%, P = .001) and a lower ER proportion (62.5% vs 78.1%, P = .027) were observed in Group 2. By univariate analysis, both T status and N status, stimulated thyroglobulin and time interval were significant risk factors for IR (P < .05). Multivariate analysis demonstrated that the time interval was an independent risk factor for IR (P = .008). CONCLUSIONS: Delayed initial RAI therapy (≥3 months after thyroidectomy) related to incomplete response in low- to intermediate-risk DTC.