FDA OKs First Therapy To Treat Tumor-induced Osteomalacia

(RTTNews) - Biopharmaceutical company Ultragenyx Pharmaceutical Inc. said the U.S. Food and Drug Administration (FDA) approved its bone disease drug Crysvita (burosumab) in the form of injection for the treatment of tumor-induced osteomalacia (TIO) in patients aged two and older.

Japanese specialty pharmaceutical company Kyowa Kirin Co., Ltd. is in collaboration with Ultragenyx in the development and commercialization of Crysvita globally based on the collaboration and license agreement between the parties.

This is the first approved therapy in the U.S. for patients with TIO who cannot undergo surgical removal of tumors. TIO is a rare disease caused by typically non-malignant, slow-growing tumors that produce excess levels of fibroblast growth factor 23 (FGF23), which is involved in phosphate reabsorption.

TIO symptoms include severe hypophosphatemia (low levels of phosphate in the blood), osteomalacia (softening of the bones), muscle weakness, fatigue, bone pain and fractures.

Crysvita is now approved for the treatment of FGF23-related hypophosphatemia in TIO associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized in adults and pediatric patients 2 years of age and older.

Crysvita is a human antibody that blocks excess activity of FGF23, a hormone that causes phosphate urinary excretion and suppresses active vitamin D production by the kidney.

There are an estimated 500 to 1,000 people in the U.S. with TIO, and approximately half of all cases are believed to be inoperable. In patients for whom the tumor or lesion is inoperable, the current treatment consists of oral phosphate and/or active vitamin D replacement.

This is the second FDA-approved indication for Crysvita. The first approval was in April 2018 for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients one year of age and older. The XLH indication was expanded in September 2019 to include infants as young as six months of age.

The FDA approval of Crysvita for TIO was based on data from two single-arm Phase 2 studies, a 144-week study in 14 adult patients conducted by Ultragenyx in the U.S. and an 88-week study in 13 adult patients conducted by Kyowa Kirin in Japan and South Korea.

In both studies, Crysvita was associated with increases in serum phosphorus and serum 1,25-dihydroxyvitamin D levels. Increased phosphate levels led to improvements in osteomalacia. The tumors associated with TIO release a peptide hormone-like substance known as FGF23 that lowers phosphate levels.