Background: The role of hormone replacement therapy (HRT) in women who have been treated for breast cancer remains controversial. The addition of tamoxifen may protect these women from any proliferative effect of exogenous oestrogen on the breast. The aim of this analysis was to determine if tamoxifen and HRT may be safely administered together.
Methods: We studied the interaction between HRT and tamoxifen on serum cholesterol, fibrinogen, antithrombin III (AT III) and bone mineral density (BMD) in postmenopausal healthy women enrolled in a randomised tamoxifen chemoprevention trial.
Results: Tamoxifen decreased serum cholesterol by a mean of 13% from pretreatment values (n = 153). The addition of HRT to tamoxifen did not result in further reduction in serum cholesterol (n = 20). HRT alone led to a reduction of serum cholesterol by a mean of 5% in 14 women on placebo. The addition of tamoxifen to HRT resulted in further reduction in serum cholesterol by a mean of 7% (n = 44). Significant reductions of plasma fibrinogen by 14% and AT III by 8% were seen in women who received tamoxifen. There were no further significant changes in these coagulation factors in women on tamoxifen/HRT combinations. Tamoxifen resulted in an annual increase in BMD of the femur and spine by 2% and 1.5%, respectively, when compared to placebo (n = 38). The addition of HRT to tamoxifen resulted in further 2% annual increase in BMD of the femur.
Conclusions: We conclude that there were no significant adverse intereactions with tamoxifen and HRT in this small series of patients. The combination results in a reduction of serum cholesterol, increase in BMD especially in the femur and appears not to have any adverse effect on coagulation factors. Multicentre studies should be conducted to evaluate the effect of this combination on relieving menopausal symptoms, disease relapse and overall survival in women who have received treatment for breast cancer.