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Abstract: FR-PO677

Hypophosphatemia from a Liver Spindle Cell Tumor: A Novel Site for FGF23-Related Tumor-Induced Osteomalacia

Session Information

Category: Trainee Case Report

  • 1500 Onco-Nephrology

Authors

  • Leidner, Alexander S., Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
  • Langman, Craig B., Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
  • Martin, Aline, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
  • David, Valentin, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
  • Wertheim, Jason, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
  • Price, Heather, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
  • Aggarwal, Vikram, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
Introduction

Tumor induced osteomalacia(TIO), presenting with hypophosphatemia driven by fibroblast growth factor 23(FGF23) production is a paraneoplastic phenomenon. We present a liver tumor with demonstrated FGF23 production, a previously unreported site.

Case Description

A 58 y/o female with a history of lupus and osteoporosis presented with fatigue, weight loss and joint pains. Medications include alendronate, plaquenil and vitamin D. She was found to have 3.6g of 24 hour urine protein and low phosphorous for four years. Fractional excretion of phosphate ranged between 40-60 % (normal 10-20%) on several occasions during a period of 3 months.. Renal biopsy was performed and revealed proximal tubule vacuolation, without evidence of lupus activity. C-terminal FGF23 levels were tested at multiple points and elevated to 97 and 770 RU/ML at a serum phosphorous of 1.7 and 3.4 mg/dL respectively on high dose supplementation. Parathyroid hormone and vitamin D levels were normal. FGF23 levels remained elevated. Ga-68 dotatate PET scan revealed an irregular enhancing liver mass which upon resection was a spindle cell tumor with clear margins. Immunohistochemical stain of the pathologic tissue was positive for FGF23 when compared to normal liver. Cell culture of tumor cells versus the patients normal liver cells showed two-fold higher FGF23 expression.The intra-op & post-op period was uneventful except worsening of hypophosphatemia as expected with increase in FGF23 to 800-1400 RU/ml. 3 months post-op, she had a minor fall with an avulsion fracture of the 5th metatasrsal base. 5 months later the patient remains hypophosphatemic, but requires less oral supplementation. Symptoms have improved significantly, however her FGF 23 remains elevated.

Discussion

While the liver has been shown to express FGF23, TIO has not been previously described as a consequence of a liver neoplasm. TIO is a potentially curable paraneoplastic etiology of symptomatic hypophosphatemia. Symptoms usually remit quickly in tumors in which resection is possible. This adds to potential sites to explore when evaluating for TIO. Repeat PET scan will be required to evaluate our patient for residual disease given continued FGF23 elevation. Recombinant FGF23 antibody is another potential intervention if other methods of cure are impossible.