Importance: Suppression of thyrotropin (often referred to as thyroid-stimulating hormone, or TSH) with levothyroxine used in management of intermediate- and high-risk differentiated thyroid cancer (DTC) to reduce the likelihood of progression and death is based on conflicting evidence. Objective: To examine a cohort of patients with intermediate- and high-risk DTC to assess the association of thyrotropin suppression with progression-free survival (PFS) and overall survival. Design, Setting, and Participants: This cohort study used a multicenter database analysis including patients from tertiary referral centers and local clinics followed up for a mean (SD) of 7.2 (5.8) years. Patients with DTC treated uniformly with total thyroidectomy and radioactive iodine between January 1, 1979, and March 1, 2015, were included. Among the 1012 patients, 145 patients were excluded due to the lack of longitudinal thyrotropin measurements. Exposures: Levothyroxine therapy to target thyrotropin suppression with dose adjustments based on changing thyrotropin goal. Main Outcomes and Measures: The primary outcome measures were overall survival and PFS. A Cox proportional hazards model was used to assess the contribution of age, sex, tumor size, histology, and lymph node and distant metastases at landmarks 1.5, 3.0, and 5.0 years. The patients were divided into 3 groups based on mean thyrotropin score before each landmark: (1) suppressed thyrotropin, (2) moderately suppressed or low-normal thyrotropin, and (3) low-normal or elevated thyrotropin. Results: Among 867 patients (557 [64.2%] female; mean [SD] age, 48.5 [16.5] years) treated with a median (range) cumulative dose of 151 (30-1600) mCi radioactive iodine, disease progression was observed in 293 patients (33.8%), and 34 patients (3.9%) died; thus, the study was underpowered in death events. Thyrotropin suppression was not associated with improved PFS at landmarks 1.5 (P = .41), 3.0 (P = .51), and 5.0 (P = .64) years. At 1.5 and 3.0 years, older age (hazard ratio [HR], 1.06; 95% CI, 1.03-1.08 and HR, 1.05; 95% CI, 1.01-1.08, respectively), lateral neck lymph node metastases (HR, 4.64; 95% CI, 2.00-10.70 and HR, 4.02; 95% CI, 1.56-10.40, respectively), and distant metastases (HR, 7.54; 95% CI, 3.46-16.50 and HR, 7.10; 95% CI, 2.77-18.20, respectively) were independently associated with subsequent time to progression, while at 5.0 years, PFS was shorter for patients with lateral neck lymph node metastases (HR, 3.70; 95% CI, 1.16-11.90) and poorly differentiated histology (HR, 71.80; 95% CI, 9.80-526.00). Conclusions and Relevance: Patients with intermediate- and high-risk DTC might not benefit from thyrotropin suppression. This study provides the justification for a randomized trial.
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