"As the first FDA-approved therapy to treat this debilitating disease, today’s action is an important step in finding treatment options for patients living with tumor-induced osteomalacia whose tumor cannot be found or removed."
The FDA has approved burosumab-twza (Crysvita) for the treatment of patients aged 2 years and older with tumor-induced osteomalacia (TIO).
TIO is a rare disease that leads to the development of tumors that cause weakened and softened bones. The tumors that develop due to TIO release FGF23, which regulates patients’ phosphate levels; when the phosphate levels are too low, the bones begin to soften and weaken.
“Treatment for TIO focuses on identifying and removing the tumor that causes the disease. However, when that is not possible, Crysvita can help increase the levels of phosphate in the blood,” said Theresa E. Kehoe, MD, acting director of the Division of General Endocrinology in the FDA’s Center for Drug Evaluation and Research, in a statement. “As the first FDA-approved therapy to treat this debilitating disease, today’s action is an important step in finding treatment options for patients living with TIO whose tumor cannot be found or removed.”
Data supporting the approval come from 2 studies in which 27 adult patients with TIO received burosumab every 4 weeks. Both studies looked at the rate of patients whose phosphate levels returned to normal. In the first study, at week 24, 50% of patients had achieved normal phosphate levels which were maintained at or near-normal levels through week 144. In the second study, 69% of patients achieved normal phosphate levels at week 24 and maintained these levels or close to normal levels through week 88. Additionally, in the first study bone studies showed evidence of healing of the bone lesions resulting from the osteomalacia.
Common adverse events reported with burosumab include tooth abscess, muscle spasms, dizziness, constipation, injection site reaction, rash, and headaches. Rash, hives, and other signals of hypersensitive reactions have been reported with burosumab treatment. If these events become serious, patients are recommended to stop treatment with burosumab and discuss next steps with a health care provider. Higher than usual levels of phosphorus have also been seen and may be associated with an increased risk of nephrocalcinosis.
The FDA suggests that patients taking oral phosphate or active vitamin D, those who have serum phosphate levels within or above the normal range for their age, and those with severe kidney impairment or end-stage renal disease should not take burosumab.
Burosumab is also approved by the FDA for the treatment of adult and pediatric patients aged 6 months and older who have X-linked hypophosphatemia, which causes low levels of phosphate in the blood and leads to impaired bone growth and development in children and teenagers.
FDA Approves First Therapy for Rare Disease that Causes Low Phosphate Blood Levels, Bone Softening. News release. FDA. June 18, 2020. Accessed June 23, 2020. https://bit.ly/3hSTCI0