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Tumor-Induced Osteomalacia (TIO / Oncogenic Osteomalacia)

Paraneoplastic FGF23 excess from a small mesenchymal tumor causing renal phosphate wasting.

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

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This content is for informational purposes only and does not constitute medical advice. You can book an appointment at our Endokrinoloji department. Book Appointment →

What is Tumor-Induced Osteomalacia (TIO / Oncogenic Osteomalacia)?

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome in which a phosphaturic mesenchymal tumor (PMT-MCT subtype) over-secretes fibroblast growth factor 23 (FGF23), driving renal phosphate wasting and impaired 1,25-(OH)2 vitamin D synthesis.

The result is chronic hypophosphatemia, defective bone mineralization (osteomalacia in adults, rickets-like changes in children), proximal muscle weakness and disabling bone pain. Tumors are typically tiny, slow-growing and notoriously hidden in extremities, sinuses, head and neck, or skull base.

Cure is achieved with complete tumor resection, but localization with whole-body Ga-68 DOTATATE PET/CT or 18F-FDG PET is challenging and often delayed by years. Burosumab (anti-FGF23 monoclonal antibody) is now approved when surgery is impossible.

Symptoms

Progressive bone pain and fragility fractures
Proximal muscle weakness and waddling gait
Loss of height and kyphosis
Chronic fatigue
Difficulty climbing stairs
Bone tenderness in ribs, hips, lower back
Pseudofractures (Looser zones) on imaging

Risk Factors

Adult-onset hypophosphatemia without known cause
Long-standing idiopathic osteomalacia
Phosphaturic mesenchymal tumor
PMT-MCT histopathology (mixed connective tissue variant)
Tumor in extremities, sinuses or skull base
Adult age 40-60 years
No family history of hypophosphatemia

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Unexplained adult bone pain with low phosphorus
  • Pathologic or low-trauma fractures
  • Progressive proximal muscle weakness
  • Vitamin D therapy not correcting symptoms
  • Inappropriately normal/elevated FGF23 with hypophosphatemia
  • Need for tumor localization imaging (Ga-68 DOTATATE PET)

Treatment Methods

01
Surgical resection of the offending tumor (curative)
02
Oral phosphate supplementation 4-6 times daily
03
Active vitamin D (calcitriol or alfacalcidol)
04
Burosumab (anti-FGF23 monoclonal antibody) when surgery fails
05
Cinacalcet adjunct in refractory hyperparathyroidism
06
Localization with Ga-68 DOTATATE PET/CT and venous sampling
07
Cryoablation or radiofrequency ablation for inaccessible tumors
08
Long-term metabolic and skeletal monitoring

Which Department to Visit?

You can visit our Endokrinoloji department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.