Appropriate dosing of burosumab in tumor-induced osteomalacia

We appreciated the recently published paper of Crotti and coworkers in which the authors reported a patient with tumor-induced osteomalacia (TIO) treated with burosumab for over 2 years for a tumor located in the pre-sacral region that recurred 18 months after excision. Recurrence was associated with decline of serum phosphate (SP) and increase of serum FGF23. After 4 years of treatment with calcitriol and phosphorus supplements without SP normalization, burosumab was started “at the dose of 0.3 mg/kg/month.” The starting dose of burosumab used in this patient was the same used in two previous trials on TIO adult patients. However, in these studies, the overall effects were not completely satisfactory.