UX023T-CL201
This open-label study showed that an antibody blocking the phosphate-wasting hormone FGF23 raised blood phosphate to normal and helped heal fractures in adults whose soft-bone disease was driven by a small tumour that could not be located or removed, which supported Crysvita for that cancer-care use.
Overview
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.
- Burosumab: 0.8 mmol/L.
- The p-value (<0.0001) says a difference this large would rarely happen by chance; it does not say how large or how useful the difference is.
- 33 out of 100 people reached this endpoint with Burosumab.
- There was no comparison group, so this number cannot tell you how much of the effect is due to the treatment.
- This endpoint is not one of the standard survival or response measures; read it alongside the trial's primary result.
- These results apply to the people the trial enrolled: Adults with tumour-induced osteomalacia from phosphaturic mesenchymal tumours that cannot be found or removed: open-label burosumab with dose titration, for FGF23-driven phosphate wasting. People in a different situation may not see the same effect.
- Only 14 people took part, so the numbers are less certain than in a large trial.
Numbers are from the trial as recorded here; see the source links in the table below. This is orientation, not medical advice: ask your team how closely the trial population matches you.
14 analysed.
Baseline 0.52 mmol/L; 0.91 mmol/L at week 22 after dose titration
SourceOf 249 fractures or pseudofractures present at baseline across 14 patients; a further 13% partially healed
Source| Endpoint | Arm | n | Value | HR (95% CI) | p | Source |
|---|---|---|---|---|---|---|
| Mean serum phosphorus at week 144 (tumour-induced osteomalacia cohort)primary | Burosumab | 14 | 0.82 mmol/L | - | <0.0001 | link |
| Baseline fractures or pseudofractures fully healed at week 144 | Burosumab | 14 | 33% | - | - | link |
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