This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Oncogenic osteomalacia is characterized by the development of a tumor that causes the bones to be weakened. This occurs when a tumor secretes a substance called fibroblast growth factor 23 (FGF23). FGF23 inhibits the ability of the kidneys to absorb phosphate. Phosphate is important for keeping bones strong and healthy. Therefore, this disease is characterized by a softening and weakening of the bones (osteomalacia). The disease also results in multiple biochemical abnormalities including high levels of phosphate in the urine (hyperphosphaturia) and low levels of phosphate in the blood (hypophosphatemia). The majority of tumors that cause oncogenic osteomalacia are small and slow-growing. These tumors most commonly occur in the skin, muscles, or bones of the extremities or in the paranasal sinuses around the head. Most of these tumors are benign, meaning they are not associated with cancer.
The exact reason that the tumors associated with oncogenic osteomalacia develop is not known. The disease is diagnosed when a person experiences clinical features such as bone weakening and hyperphosphaturia and a tumor is found by imaging of the body. Treatment of the disease consists of surgical removal of the tumor. The symptoms of the disease, including the weakening of the bones, typically resolve once the tumor is removed.
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