Research in Medicine

Background : While tamoxifen has been shown to alter concentration of many hormones and their binding globulins, there have been conflicting results on its effects on the thyroid function tests. We attempted to clarify these effects by studying subject in an uncontrolled clinical trial.

 Materials and methods : We evaluated 64 women with breast cancer who had participated in a nonrandomized pretest posttest study. They were given 20 mg tamoxifen orally daily at least for 12 months. Measurement of thyroid stimulation hormone (TSH), free thyroxin index (FTI), thyroxin (T₄) and three idothyronin (T₃) were made for each subject before and after 6 and 12 months of treatment.

Results : Results revealed that T4 level has significantly increased 6 months, but not 12 months, following the therapy (p<0.0001). Meanwhile, T₃ and TSH levels remained unchanged during the follow up period (NS). FTI results showed a significant increase in the mean value within the normal range after one year (p<0.005).

Conclusion : Tamoxifen may induce increased level of FTI within the first year of treatment, however, this change is within the normal level. Moreover, T₄ increased during the first 6 months but return within the normal range after 12 months.