UX023T-CL201

UX023T-CL201 (NCT02304367; US Crysvita label Study 6) was a multicentre, open-label, phase 2 study of burosumab, a fully human monoclonal antibody that inhibits FGF23, in adults with tumour-induced osteomalacia or cutaneous skeletal hypophosphataemia syndrome. The Journal of Bone and Mineral Research 2021 report focuses on 14 patients with tumour-induced osteomalacia, excluding two diagnosed with X-linked hypophosphataemia after enrolment and one with cutaneous skeletal hypophosphataemia syndrome.

Key endpoints were changes in serum phosphorus and osteomalacia on transiliac bone biopsy at week 48. Mean serum phosphorus rose from 0.52 mmol/L at baseline and was maintained after dose titration from week 22 (0.91 mmol/L) to week 144 (0.82 mmol/L, p less than 0.0001). Most histomorphometric measures of osteomalacia improved at week 48 (osteoid volume per bone volume, osteoid thickness and mineralisation lag time fell; osteoid surface per bone surface did not change). Of 249 fractures or pseudofractures present at baseline across the 14 patients, 33 percent were fully healed and 13 percent partially healed at week 144. Patients reported less pain and fatigue and better physical health. Two patients discontinued; 16 serious adverse events occurred in seven patients and there was one death, all judged unrelated to treatment; nine patients had 16 treatment-related adverse events, all mild or moderate.

The registry lists the study as a completed single-group phase 2 with 17 participants and conditions of tumour-induced osteomalacia and epidermal nevus syndrome, neither a corpus cancer, which is why the automated pass never attached it to the burosumab record.