Bone effect of adjuvant tamoxifen, letrozole or letrozole plus zoledronic acid in early-stage breast cancer: the randomized phase 3 HOBOE study

To measure bone mineral density (BMD) reduction produced by letrozole as compared with tamoxifen and the benefit of the addition of zoledronic acid. A phase 3 trial comparing tamoxifen, letrozole or letrozole + zoledronic acid in patients with hormone receptor-positive early breast cancer was conducted; triptorelin was given to premenopausal patients. Two comparisons were planned: letrozole versus tamoxifen and letrozole + zoledronic acid versus letrozole. Primary end point was the difference in 1-year change of T-score at lumbar spine (LTS) measured by dual energy X-ray absorptiometry scan. Out of 483 patients enrolled, 459 were available for primary analyses. Median age was 50 (range 28-80). The estimated mean difference (95% confidence interval [CI]) in 1-year change of LTS was equal to -0.30 (95% CI -0.44 to -0.17) in the letrozole versus tamoxifen comparison (P < 0.0001) and to +0.60 (95% CI +0.46 to +0.77) in the letrozole + zoledronic acid versus letrozole comparison (P < 0.0001). Bone damage by letrozole decreased with increasing baseline body mass index in premenopausal, but not postmenopausal, patients (interaction test P = 0.004 and 0.47, respectively). In the HOBOE (HOrmonal BOne Effects) trial, the positive effect of zoledronic acid on BMD largely counteracts damage produced by letrozole as compared with tamoxifen. Letrozole effect is lower among overweight/obese premenopausal patients.