Effect of tamoxifen on breast tissue density in premenopausal breast cancer.

It has been established that hormone replacement therapy (HRT) increases breast tissue density on mammography in up to 30% of women receiving treatment. The effects of selective estrogen receptor modulators (SERMs) on breast tissue have received limited attention, although there have been several reports of tamoxifen decreasing mammographic tissue density in some women undergoing adjuvant or prophylactic breast cancer treatment. We report a case of a premenopausal woman treated with tamoxifen for 5 years whose mammographic density decreased while on tamoxifen and returned to her baseline density following termination of the drug. A regression of breast tissue may be reflective of sensitivity to tamoxifen and possibly, indicative of therapeutic benefit associated with treatment. Furthermore, induction of a more radiolucent pattern by tamoxifen may independently benefit women by enhancing mammographic detection. The clinical significance of resumption of a dense breast pattern following discontinuation of tamoxifen remains to be determined.