Effects of thyroid hormone suppression therapy on adverse clinical outcomes in thyroid cancer

BACKGROUND. Long-term thyroid hormone (TH) therapy aiming at the suppression of serum thyrotropin (TSH) has been traditionally used in the management of well differentiated thyroid cancer (ThyrCa). However, formal validation of the effects of thyroid hormone suppression therapy (THST) through randomized controlled trials is lacking. Additionally, the role--if any--of TSH effect at low ambient concentrations upon human thyroid tumorigenesis remains unclear. AIM: Evaluation of the effect of THST on the clinical outcomes of papillary and/or follicular ThyrCa. METHODS. By using a quantitative research synthesis approach in a cumulative ThyrCa cohort, we evaluated the effect of THST on the likelihood of major adverse clinical events (disease progression/recurrence and death). A total of 28 clinical trials published during the period 1934-2001 were identified; only 10 were amenable to meta-analysis. Causality was assessed by Hill criteria. RESULTS: Out of 4, 174 patients with ThyrCa, 2, 880 (69%) were reported as being on THST. Meta-analysis showed that the group of patients who received THST had a decreased risk of major adverse clinical events (RR = 0.73; CI = 0.60-0.88; P < 0.05). Further, by applying a Likert scale, 15/17 interpretable studies showed either a 'likely' or 'questionable' beneficial effect of THST. Assessment of causality between TSHT and reduction of major adverse clinical events suggested a probable association. CONCLUSIONS: THST appears justified in ThyrCa patients following initial therapy. As most primary studies were imperfect, future research will better define the effect of THST upon ThyrCa clinical outcomes.