Endogenous thyrotropin and triiodothyronine concentrations in individuals with thyroid cancer

Thyroid hormone suppression therapy is associated with decreased recurrence rates and improved survival in patients with differentiated thyroid cancer. Recently higher baseline thyrotropin (TSH) levels have been found to be associated with a postoperative diagnosis of differentiated thyroid cancer. Our objective was to confirm whether preoperative TSH levels were higher in patients who were diagnosed with differentiated thyroid cancer after undergoing thyroidectomy, compared with patients who were found to have benign disease. We also sought to determine whether thyroid hormone levels were lower in the patients with malignancy.

The study was a retrospective analysis of a prospective study. The study setting was the General Clinical Research Center of an Academic Medical Center. Participants were 50 euthyroid patients undergoing thyroidectomy. Thyroxine, triiodothyronine (T(3)), and TSH levels were documented in patients prior to their scheduled thyroidectomy. Following thyroidectomy, patients were divided into those with a histologic diagnosis of either differentiated thyroid cancer or benign disease. Preoperative thyroid profiles were correlated with patients' postoperative diagnoses.

All patients had a normal serum TSH concentration preoperatively. One-third of the group was diagnosed with thyroid cancer as a result of their thyroidectomy. These patients had a higher serum TSH level (mean = 1.50 mIU/L, CI 1.22-1.78 mIU/L) than patients with benign disease (mean = 1.01 mIU/mL, CI 0.84-1.18 mIU/L). There was a greater risk of having thyroid cancer in patients with TSH levels in the upper three quartiles of TSH values, compared with patients with TSH concentrations in the lowest quartile of TSH values (odd ratio = 8.7, CI 2.2-33.7). Patients with a thyroid cancer diagnosis also had lower T(3) concentrations measured by liquid chromatography tandem mass spectrometry (mean = 112.6 ng/dL, CI 103.8-121.4 ng/dL) than did patients with a benign diagnosis (mean 129.9 ng/dL, CI 121.4-138.4 ng/dL).

These data confirm that higher TSH concentrations, even within the normal range, are associated with a subsequent diagnosis of thyroid cancer in individuals with thyroid abnormalities. This further supports the hypothesis that TSH stimulates the growth or development of thyroid malignancy during its early or preclinical phase. We also show for the first time that patients with thyroid cancer also have lower T(3) levels than patients with benign disease.