A Multicenter, Randomized, Controlled Trial for Assessing the Usefulness of Suppressing Thyroid Stimulating Hormone Target Levels after Thyroid Lobectomy in Low to Intermediate Risk Thyroid Cancer Patients (MASTER): A Study Protocol

Background: Postoperative thyroid stimulating hormone (TSH) suppression therapy is recommended for patients with intermedi ate- and high-risk differentiated thyroid cancer to prevent the recurrence of thyroid cancer. With the recent increase in small thyroid cancer cases, the extent of resection during surgery has generally decreased. Therefore, questions have been raised about the efficacy and long-term side effects of TSH suppression therapy in patients who have undergone a lobectomy. Methods: This is a multicenter, prospective, randomized, controlled clinical trial in which 2,986 patients with papillary thyroid can cer are randomized into a high-TSH group (intervention) and a low-TSH group (control) after having undergone a lobectomy. The principle of treatment includes a TSH-lowering regimen aimed at TSH levels between 0.3 and 1.99 μIU/mL in the low-TSH group. The high-TSH group targets TSH levels between 2.0 and 7.99 μIU/mL. The dose of levothyroxine will be adjusted at each visit to maintain the target TSH level. The primary outcome is recurrence-free survival, as assessed by neck ultrasound every 6 to 12 months. Secondary endpoints include disease-free survival, overall survival, success rate in reaching the TSH target range, the pro portion of patients with major cardiovascular diseases or bone metabolic disease, the quality of life, and medical costs. The follow-up period is 5 years. Conclusion: The results of this trial will contribute to establishing the optimal indication for TSH suppression therapy in low-risk papillary thyroid cancer patients by evaluating the benefit and harm of lowering TSH levels in terms of recurrence, metabolic com-plications, costs, and quality of life.