Background: It has previously been shown that higher serum TSH is associated with increased thyroid cancer incidence and advanced-stage disease. In the healthy adult population, mean TSH increases with age. As age over 45 years is a known prognostic indicator for thyroid cancer, it is important to know whether higher TSH in patients with thyroid cancer occurs independent of age.
Objective: To determine the relationship between higher TSH, cancer and age.
Design: A retrospective cohort study.
Patients and methods: A total of 1361 patients underwent thyroid surgery between May 1994 and December 2007 at a single institution. Of these patients, 954 had pathological data, preoperative TSH and complete surgical history available. Data were analysed in relation to age and TSH.
Results: Mean TSH was significantly higher in cancer patients regardless of age < 45 years or >or= 45 years (P = 0.046 and P = 0.027, respectively). When examining age groups < 20, 20-44, 45-59 and >or= 60 years, there was a trend of rising mean TSH with age. Despite the rise in the benign subgroups, mean TSH was consistently higher in those with cancer vs. those without. On multivariate analysis, higher TSH was independently associated with cancer (P = 0.039) and pathological features of Hashimoto's thyroiditis (P = 0.001) but not with age (P = 0.557). On multivariate analysis of high-risk features associated with poor prognosis, there was a significant association between higher TSH and extrathyroidal extension (P = 0.002), whereas there was no clear relationship with age, tumour size > 4 cm, and distant metastases.
Conclusion: Independent of age, thyroid cancer incidence correlates with higher TSH. Higher TSH is associated with extrathyroidal extension of disease.