Effects of Up to 5 Years of Denosumab Treatment on Bone Histology and Histomorphometry: The FREEDOM Study Extension

Denosumab reduced bone resorption, increased bone mineral density (BMD), and decreased new vertebral, hip, and nonvertebral fracture risk in postmenopausal women with osteoporosis in the FREEDOM trial. Consistent with its mechanism of action, transiliac crest bone biopsies from subjects treated with denosumab for 1 to 3 years demonstrated reduced bone turnover that was reversible upon treatment cessation. Long-term denosumab treatment for up to 6 years in the FREEDOM extension provides sustained bone turnover reduction and continued low fracture incidence. Here, we evaluate 5 years of denosumab treatment on bone remodeling at the tissue level. Transiliac crest bone biopsies were obtained from 41 subjects (13 cross-over and 28 long-term from the FREEDOM placebo and denosumab groups, respectively) at year 2 of the FREEDOM extension, representing up to 5 years of denosumab treatment. Demographics for this subset were comparable to the overall extension cohort. The mean (SD) duration from the last denosumab dose to the first dose of tetracycline was 5.7 (0.5) months. Qualitative bone histology assessed in all biopsy samples was unremarkable, showing normally mineralized lamellar bone. Structural indices, including trabecular bone volume, number, and surface, were similar between cross-over and long-term groups. Bone resorption was decreased as reflected by eroded surface in cross-over and long-term subjects. A total of 11 of 13 (85%) cross-over subjects and 20 of 28 (71%) long-term subjects had specimens with double or single tetracycline label in trabecular and/or cortical compartments; specimens from 5 cross-over subjects and 10 long-term subjects were evaluable for dynamic trabecular bone parameters. Dynamic remodeling indices were low for both groups and consistent with reduced bone turnover with denosumab. In conclusion, denosumab treatment through 5 years resulted in normal bone quality with reduced bone turnover. These observations are consistent with its mechanism of action and associated with continued BMD increases and low fracture incidence. (C) 2014 American Society for Bone and Mineral Research.