title: Preoperative tumor localization by means of venous sampling for fibroblast growth factor-23 in a patient with tumor-induced osteomalacia.
abstract: OBJECTIVE
  To report on a novel strategy for tumor localization in a 62-year-old man with hypophosphatemic tumor-induced osteomalacia (TIO).
  
  
  METHODS
  Repeated computed tomographic and magnetic resonance imaging scans failed to localize any tumor in a patient with adult-onset hypophosphatemic osteomalacia. Therefore, venous sampling for fibroblast growth factor-23 (FGF23)--a circulating hormone that has been identified as a causative factor for TIO--in major veins was conducted. Serum FGF23 was measured from collected samples by an intact FGF23 enzyme-linked immunosorbent assay.
  
  
  RESULTS
  Venous sampling suggested a local increase in serum FGF23 in the left femoral vein; this finding prompted performance of octreotide scintigraphy restricted to the left leg. A tumor was located at the lateral condyle of the left femur, which was also confirmed by magnetic resonance imaging. Surgical resection of the tumor normalized the serum phosphorus and 1,25-dihydroxyvitamin D3 levels within 5 to 10 days, and FGF23 declined to normal levels within 24 hours. Histologic analysis supported the diagnosis of a soft-tissue giant cell tumor.
  
  
  CONCLUSIONS
  Our study case demonstrates the diagnostic complexity and difficulties in localizing a small tumor in a patient with TIO. Venous sampling for FGF23 may be helpful in tumor localization in sporadic cases of hypophosphatemic osteomalacia, especially when noninvasive diagnostic techniques prove insufficient.
authors.affiliation: Department of Medical Sciences, Uppsala University Hospital, Uppsala, Sweden.
authors.forename: Per-Anton
authors.initials: PA
authors.lastname: Westerberg
authors.forename: Hannes
authors.initials: H
authors.lastname: Olauson
authors.forename: Göran
authors.initials: G
authors.lastname: Toss
authors.forename: Björn
authors.initials: B
authors.lastname: Wikström
authors.forename: Ollallo
authors.initials: O
authors.lastname: Morales
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Linde
authors.forename: Kenneth
authors.initials: K
authors.lastname: Jonsson
authors.forename: Osten
authors.initials: O
authors.lastname: Ljunggren
authors.forename: Tobias E
authors.initials: TE
authors.lastname: Larsson
mesh_terms: D014408:Biomarkers, Tumor / Q000097:blood; D001859:Bone Neoplasms / Q000097:blood* / Q000150:complications / Q000175:diagnosis*; D005269:Femur; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D018212:Giant Cell Tumor of Bone / Q000097:blood* / Q000150:complications / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010018:Osteomalacia / Q000097:blood* / Q000209:etiology
chemical_list: D014408:Biomarkers, Tumor; C000717427:FGF23 protein, human; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23