Effect of adjuvant tamoxifen therapy on thyroid function in postmenopausal women with breast cancer

Serum thyroid-stimulating hormone (TSH), free thyroxine (FT4) and total tri-iodothyronine (TT3) concentrations were measured in 45 postmenopausal breast cancer patients before adjuvant treatment with tamoxifen and at 3- and 6-month intervals. A significant increase in TSH (p = 0.002) at the end of 3 months and a subsequent decrease at the end of 6 months was noted. There were no significant changes in TT3 and FT4. We concluded that tamoxifen therapy in postmenopausal women may result in a reversible increase in TSH after 3 months.