Changes in Thyroid Functional Tests in Breast Cancer Patients under Tamoxifen Therapy

Background: Tamoxifen, a synthetic anti-estrogen agent, is administered as an adjuvant treatment in breast cancer. Since various studies have indicated that Tamoxifen can change some hormones and bound globolines, controversial results have been achieved using this medicine on Thyroid Functional Tests (TFT). The present study was conducted to investigate the effects of Tamoxifen on TFT in women with breast cancer referred to oncology clinic in Imam Hossein hospital between 2001 and 2002.

Method: A quasi-experimental clinical trial study was performed on 23 women with breast cancer in a single blind basis (with no control group). Patients were under Tamoxifen 20 mg P.O. daily and their serum TSH, free T4 and three Iodothyronine (T3) were assessed before treatment with Tamoxifen and after 3 months. Paired T test was used for statistical analysis.

Results: There was a significant difference in T3 before and after the treatment with Tamoxifen (p=0.02), whereas no significant differences were seen in TSH (p=0.095) and FT4 (p=0.13).

Discussion: This study showed that treatment with Tamoxifen in women suffering from breast cancer results in an increase in serum T3 but has no effect on serum TSH and FT4, therefore women under treatment with Tamoxifen remain euthyroid.