Two or three weeks of thyroid hormone withdrawal before initial 131I therapy for patients with differentiated thyroid carcinoma?

Objective To evaluate the effects of different thyroid hormone withdrawal (THW) duration before initial I-131 therapy on the level of thyrotropin (TSH), biochemical parameters and prognosis in patients with differentiated thyroid cancer (DTC). Methods DTC patients who underwent total thyroidectomy between January 2016 and August 2018 before initial I-131 therapy were included. Patients undergoing two-week and three-week THW were categorized into groups A and B. Factors influencing TSH >= 30 mIU/L, changes in biochemical parameters before surgery and after THW, and prognosis after I-131 therapy were evaluated and compared. Results Totally, 95.3% (303/318) of patients had TSH >= 30 mIU/L after THW. The rate of TSH >= 30 mIU/L in groups A and B was 93.8% (152/162) and 96.8% (151/156), respectively (P = 0.212). Age was the only factor influencing TSH >= 30 mIU/L (hazard ratio [HR] 0.937, 95% confidence interval [CI] 0.882-0.997, P = 0.038). Changes of creatinine, alanine aminotransferase, aspartate aminotransferase, cholesterol, high-density lipoprotein and low-density lipoprotein before and after THW were higher in group B than in group A (all P < 0.05). After a median follow-up of 55 months, the rate of disease persistence/recurrence in groups A and B was 6.2% (7/113) and 2.3% (3/128), respectively (P = 0.241). Stimulated thyroglobulin before I-131 therapy was the only predictor for disease persistence/recurrence (HR 1.028, 95%CI 1.012-1.043). Conclusions Two-week THW was an effective strategy to achieve TSH >= 30 mIU/L before I-131 therapy in patients younger than 50 years old and had less effect on changes in biochemical parameters, while there was no difference in the prognosis between two-week and three-week THW.