The tamoxifen paradoxinfluence of adjuvant tamoxifen on fracture risk in pre- and postmenopausal women with breast cancer

aSummaryOur data demonstrate that tamoxifen does not reduce fracture risk. Close surveillance is necessary to prevent bone loss in premenopausal women with breast cancer upon treatment initiation.IntroductionEndocrine treatment of breast cancer may interfere with bone turnover and influence fracture risk.MethodsOut of a cohort of almost 5 million patients in total, we identified 5520 women between 18 and 90years of age with breast cancer receiving tamoxifen, matched them with 5520 healthy controls using the Disease Analyzer Database, and investigated the fracture risk.ResultsWe found a cumulative incidence of fractures of 6.3% in patients aged between 18 and 50years (n=3634) treated with tamoxifen versus a cumulative incidence of 3.6% in the control group (p<0.001). As such, the risk of fracture was 75% higher for patients receiving tamoxifen than that for healthy controls (HR 1.75; 95% CI 1.25-2.48). With regard to patients aged between 55 and 90years (n=7406), the cumulative incidence of fractures in patients treated with tamoxifen was 10.1% compared to 9.3% in the control group (p=0.740), i.e., there was no significant difference between the two groups (HR 0.97; 95% CI 0.81-1.16).ConclusionsCompared to healthy controls, premenopausal women with breast cancer treated with tamoxifen showed an increased risk of fracture, while postmenopausal women on tamoxifen did not show any risk reduction.