FDA approves burosumab for tumor-induced osteomalacia
The FDA approved burosumab-twza injection to treat patients aged 2 years and older with tumor-induced osteomalacia, according to an agency press release.
Tumor-induced osteomalacia is a rare disease in which small tumors produce fibroblast growth factor 23 (FGF23), leading to phosphate wasting and impaired vitamin D synthesis. Burosumab-twza (Crysvita, Ultragenyx), a human monoclonal antibody that binds and blocks FGF23 activity, was approved in 2018 to treat X-linked hypophosphatemia (XLH), a disorder in which genetic mutations lead to elevated levels of FGF23.
“Treatment for tumor-induced osteomalacia 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,” Theresa E. Kehoe, MD, acting director of the Division of General Endocrinology in the FDA’s Center for Drug Evaluation and Research, said in the release. “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.”
As Healio previously reported, a small cohort of adults with tumor-induced osteomalacia experienced improvements in phosphate and skeletal metabolism, physical functioning and quality of life after 144 weeks of treatment with burosumab. In study data reported in a virtual presentation at ENDO Online, researchers found that mean serum phosphorus for the cohort increased from a baseline level of 1.6 mg/dL to 2.85 mg/dL at week 22 and was maintained at week 144 (mean, 2.56 mg/dL; P < .0001). Measurement of the ratio of tubular maximum reabsorption of phosphate to glomerular filtration rate, used to evaluate renal phosphate transport, also improved, as did mean levels of 1,25-dihydroxyvitamin D. Among 11 participants who underwent paired bone biopsies at baseline and week 48, osteoid volume/bone volume decreased from a mean 17.6% to 12.1% at week 48 (P = .086).
Hypersensitivity reactions, such as rash and hives, have been reported among patients who took burosumab. If serious hypersensitivity reactions occur, patients should stop taking burosumab and talk with their health care provider about further medical treatment. Additionally, higher than normal levels of phosphorus may be associated with an increased risk for nephrocalcinosis.
The most common side effects reported in adults with tumor-induced osteomalacia taking burosumab were tooth abscess, muscle spasms, dizziness, constipation, injection site reaction, rash and headaches. Individuals taking oral phosphate or active vitamin D, those who have serum phosphate levels within or above the normal range for their age, and patients with severe kidney impairment or end stage renal disease should not take burosumab.
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