Why Should Serum TSH Be a Risk Factor for Malignancy?
Serum TSH is a well-established growth factor for thyroid nodules, and suppression of serum TSH concentrations by administering exogenous thyroid hormone may interfere with the growth of established nodules as well as the formation of new thyroid nodules (13). Animal data demonstrate that TSH suppression in rats exposed to radioiodine prevents the formation of thyroid cancers (14), however there are no data in humans that suggest a protective effect of TSH suppression on oncogenesis. Suppression of serum TSH concentrations by administering exogenous thyroid hormone is associated with reduced recurrence and mortality in patients with thyroid cancer (15). It is therefore possible that the higher rate of malignancy with increasing serum TSH concentrations reflects a trophic effect of TSH on thyroid tissue that promotes neoplasia and carcinogenesis. Alternatively, lower serum TSH concentrations may be associated with autonomous function in nodules, which has been long recognized as indicat
