Effect of denosumab administration on low bone mineral density (T-score −1.0 to −2.5) in postmenopausal Japanese women receiving adjuvant aromatase inhibitors for non-metastatic breast cancer

Although adjuvant aromatase inhibitor (AI) therapy is widely used in postmenopausal women with hormone receptor-positive breast cancer, it is known to be associated with bone loss and increased fracture risk. Denosumab, a fully human monoclonal antibody against the receptor activator of nuclear factor-κB ligand, has been shown to protect against AI-induced bone loss. However, the efficacy of denosumab in the treatment of AI-associated bone loss has not been prospectively evaluated in Japan. We prospectively monitored bone mineral density (BMD) of the lumbar spine and bilateral femoral necks in 100 postmenopausal women with hormone receptor-positive postoperative breast cancer of clinical stage I–IIIA in whom treatment with AI as adjuvant endocrine therapy was planned or had been ongoing. Study participants received supplemental calcium and vitamin D every day and denosumab (60 mg) subcutaneously every 6 months. At enrollment, patients were required to have evidence of low bone mass without meeting the criteria for osteoporosis. The primary endpoint was percentage change from baseline in lumbar spine BMD at month 12. At 6 and 12 months, lumbar spine BMD increased by 3.3 and 4.7%, respectively. BMD of the femoral necks also increased. Hypocalcemia of grade ≥2, osteonecrosis of the jaw, and non-traumatic clinical fracture did not occur. In conclusion, semi-annual treatment with denosumab was associated with increased BMD in Japanese women receiving adjuvant AI therapy, regardless of prior AI treatment.