Denosumab Prevents Bone Loss and Microarchitectural Deterioration in Premenopausal Women With Breast Cancer Receiving Estradiol Suppression Therapy: A Randomized Controlled Trial

PURPOSE Suppression of ovarian function and aromatase inhibition (AI) increases disease-free survival in premenopausal women with estrogen receptor (ER)–positive early-stage breast cancer but accelerates bone loss. We therefore hypothesized that suppressing bone remodeling using denosumab (DMAB) would prevent bone loss in these women. METHODS In a 12-month double-blind randomized trial, 68 women with ER-positive early-stage breast cancer commencing ovarian function suppression and AI were randomly assigned to 60 mg DMAB (n = 34) or placebo (PBO; n = 34) once every 6 months (at 0 and 6 months). Volumetric bone mineral density (BMD), microarchitecture, and estimated bone strength of the distal tibia and distal radius were measured using high-resolution peripheral quantitative computed tomography, and spine and hip BMD were measured using dual-energy X-ray absorptiometry at 0, 6, and 12 months. The primary end point and treatment effect was the mean adjusted between group difference (MAD; [95% CI]) in distal tibial total volumetric BMD over 12 months, with a single P value tested over all time points. The study is registered with the Australian New Zealand Clinical Trials Registry (anzctr.org.au; identifier: ACTRN12616001051437). RESULTS Intention-to-treat analysis included all 68 randomly assigned women. Over 12 months, compared with PBO, DMAB prevented the decrease in distal tibial total BMD (MAD, 20.8 mg HA/cm 3 [95% CI, 17.3 to 24.2]), cortical BMD (42.9 mg HA/cm 3 [95% CI, 32.1 to 53.9]), trabecular BMD (3.32 mg HA/cm 3 [95% CI, 1.45 to 5.20], P = .004), estimated stiffness (11.6 kN/m [95% CI, 7.6 to 15.6]), and failure load (563 N [95% CI, 388 to 736]). Findings were similar at the distal radius. Decreases in BMD at the lumbar spine (MAD, 0.13 g/cm 2 [95% CI, 0.11 to 0.15]), total hip (0.08 g/cm 2 [95% CI, 0.07 to 0.09], and femoral neck (0.06 g/cm 2 [95% CI, 0.05 to 0.07]) were also prevented. All P < .001 unless otherwise noted. CONCLUSION Treatment with DMAB at commencement of estradiol suppression therapy preserves BMD, bone microarchitecture, and estimated strength, and is likely to increase fracture-free survival.