Effect of adjuvant androgen deprivation on thyroid function tests in prostate cancer patients

Androgen deprivation (AD) used in the treatment of prostate cancer is known to alter concentrations of sex hormones and their binding globulins. Less is known as to its effect on thyroid hormones. In this prospective study the effects of AD on thyroid function were clarified. Levels of serum thyroid stimulating hormone (TSH), free thyroxine (FT4) and thyroid binding globulin concentrations were measured in prostate cancer patients treated with either radical radiotherapy and androgen deprivation for 12 months (AD) or radical radiotherapy alone (RT). Measurements were made at baseline, and at 3, 6 and 12 months. At baseline and at 3 months the results of thyroid function tests did not differ significantly between groups. A significant decline in serum testosterone in the AD group was accompanied by a significant decline in FT4 at 6 and 12 months, while no significant changes in thyroid function were observed in the RT group. The decline in FT4 among AD patients did not evoke a normal TSH response. Prolonged use of AD hampers the interpretation of thyroid test results. This finding has substantial implications for the follow-up of patients in hormonally treated prostate cancer.