Tumor-Induced Osteomalacia (TIO)

Tumor-induced osteomalacia (TIO) is a rare disease typically caused by slow-growing tumors, which produce excess amounts of FGF23, a protein that regulates phosphate and vitamin D, both of which are important for bone health.

TIO tumors are often located in the extremities (for example, a hand or a foot). A TIO tumor is unlikely to spread, but can be difficult to locate by X-ray or MRI. People with TIO may experience muscle weakness, fatigue and bone pain.

Finding and removing the tumor through surgery is currently the most effective treatment for TIO since these tumors rarely spread. There is a small chance that TIO could come back, or recur, with the growth of a new tumor.

Some people use phosphate supplements and calcitriol (a form of vitamin D) to manage their symptoms.

Ultragenyx is studying investigational KRN23 for the treatment of TIO in cases where tumor removal is not possible or is incomplete.

Other names for TIO:

  • Oncogenic osteomalacia
  • Oncogenic hypophosphatemic osteomalacia