Effects of denosumab treatment and discontinuation on human growth plates.

CONTEXT: Denosumab is a humanized monoclonal antibody to receptor activator of nuclear factor-κB ligand used primarily for postmenopausal osteoporosis and skeletal-related events from metastatic cancer. Its safety in children has not been established.

OBJECTIVE

The objective of the study was to investigate the effects of denosumab treatment on skeletal growth and histology.

DESIGN

This was an observational case report with radiological and histopathological analyses.

SETTING

The study was conducted at a clinical research center.

PATIENTS: A 9-year-old boy with fibrous dysplasia treated with a 7-month course of denosumab participated in the study.

INTERVENTION: Histological analyses were performed and compared on growth plates from limbs that had been amputated before and 17 months after denosumab treatment.

MAIN OUTCOME MEASURES: Skeletal radiographs and bone histopathology from before and after treatment were measured.

RESULTS

After initiating denosumab, sclerotic metaphyseal bands appeared on radiographs. Posttreatment radiographs revealed migration of the bands away from the growth plates, consistent with continued linear growth. Histologically, the bands were composed of horizontally arranged trabeculae containing calcified cartilage. This cartilage appeared to derive from unresorbed primary spongiosa as a result of osteoclast inhibition by denosumab, similar to what has been observed with bisphosphonates. By 17 months after treatment, active bone resorption and formation had returned, as evidenced by the presence of active osteoclasts in resorption pits and osteoid surfaces.

CONCLUSIONS

Further studies are needed to determine the safety of denosumab on the growing skeleton. However, in this child there was continued epiphyseal activity both during and after treatment and reversal of bone turnover suppression after treatment discontinuation, suggesting that denosumab did not have significant adverse effects on growth.