Evidence that tamoxifen preserves bone density in late postmenopausal women with breast cancer

Tamoxifen, which is used for treating breast cancer, exhibits estrogenic an d antiestrogenic characteristics, depending on the tissue. In the human bre ast it acts as an antiestrogen. whereas estrogenic effects have been report ed on endometrium and bone. The purpose of this study was to determine whet her tamoxifen (TAM) prevents bone loss in elderly, postmenopausal women. Bo ne mineral density of the lumbar spine (SBD) was measured in elderly women (at least 10 years after menopause) 5 years after stage I or II breast canc er (n = 111). The results showed that SBD in untreated patients (n = 74) wa s significantly lower (p < 0.05) than SBD in patients (n = 37) treated with TAM over 5 years. In a subgroup of patients (n = 24) with positive estroge n receptor status, changes in SBD 12 months after discontinuation of 5-year TAM therapy were measured and compared with the changes of extended TAM tr eatment over a sixth year. Twelve months after withdrawal of 5-year TAM med ication (n = 11) bone density decreased significantly (-4.8 +/- 2.5%; p > 0 .05), whereas in the group of women (n = 13) receiving extended TAM medicat ion (20 mg) for an additional 12 months, SBD (+1.9 +/- 3.5 %) was maintaine d during the observation period, and was significantly higher when compared with the group of untreated patients (p < 0.05). We conclude that tamoxife n has a preventive effect on trabecular bone loss at the lumbar spine. when compared to age-matched data and to untreated women with breast cancer in the late menopause. Our data give evidence of benefits to bone density prov ided by prolonged administration in patients after breast cancer and at ris k of osteoporosis.