TIO is an acquired form of hypophosphatemia1
Tumor-induced osteomalacia, or TIO, is an extremely rare, difficult to diagnose disease—to date, there have only been about 1000 cases reported. The mean age of diagnosis is 45 years with a wide age range, including cases reported in children.2-4
TIO is an acquired form of hypophosphatemia caused by slow growing, benign, phosphaturic mesenchymal tumors that can be located anywhere in the body in soft tissues or bones. These tumors secrete excess fibroblast growth factor 23 (FGF23), which results in hypophosphatemia and osteomalacia.3,4
The underlying cause of hypophosphatemia in TIO
In normal homeostasis3,4:
Normal FGF23 activity
FGF23 plays an important role in phosphorus homeostasis via renal excretion
Intestinal phosphorus absorption also regulates phosphorus homeostasis
Normal bone mineralization
Tumors express increased production of FGF23
Excess FGF23 results in reduced renal phosphorus reabsorption or "phosphate wasting"
Reduced renal production of active vitamin D results in decreased intestinal phosphorus absorption
Resulting in chronic hypophosphatemia leading to osteomalacia
Tumor removal can be curative, but may not be possible under certain circumstances.2
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