Effects of denosumab on bone mineral density in Japanese women with osteoporosis treated with aromatase inhibitors for breast cancer

Adjuvant aromatase inhibitor (AI) therapy, for hormone receptor-positive breast cancer, in postmenopausal women is associated with bone loss, leading to an increased risk of fractures. Denosumab, an antibody raised against the receptor activator of nuclear factor-κB ligand, has been proven to protect against AI-induced bone loss. Hence, we aimed to determine whether denosumab is effective in postmenopausal Japanese women with osteoporosis, treated with AI. We prospectively evaluated the bone mineral density (BMD) in the lumbar spine and the bilateral femoral neck in 102 postmenopausal women with clinical hormone receptor-positive breast cancer, stages I–IIIA, during a postoperative period of 12 months. The other inclusion criteria for this study were: women that should receive AIs as adjuvant therapy and those with evidence of osteoporosis (lumbar spine or bilateral femoral neck BMD, equivalent to T-score classification of ≤ − 2.5) upon enrollment. The patients received supplemental calcium, vitamin D, and 60 mg of subcutaneous denosumab every 6 months. The BMD of the lumber spine increased by 4.9 and 6.6% at 6 and 12 months, respectively. An increase in BMD was observed at the femoral neck, bilaterally. Hypocalcemia ≥ grade 2, osteonecrosis of the jaw, and non-traumatic clinical fracture were not observed in this study. Our findings revealed that biannual treatment with denosumab is associated with a great increase of BMD in Japanese women receiving adjuvant AI therapy, irrespective of their previous history of AI therapy.