title: Oncogenic osteomalacia due to FGF23-expressing colon adenocarcinoma.
abstract: BACKGROUND
  Oncogenic osteomalacia, a paraneoplastic syndrome associated with hypophosphatemia due to increased urinary phosphate excretion, is caused by excessive synthesis and secretion of fibroblast growth factor 23 (FGF23), a phosphaturic hormone that is normally produced by osteocytes. Most cases of oncogenic osteomalacia have been associated with benign tumors of bone or soft tissue; however, whether malignant neoplasms can also produce and secrete FGF23 is currently unknown.
  
  
  OBJECTIVE
  The aim was to determine whether a malignant neoplasm could cause oncogenic osteomalacia through excessive production and secretion of FGF23.
  
  
  METHODS
  We describe an 80-year-old woman with stage IV colon adenocarcinoma who presented with severe hypophosphatemia (0.4 mg/dL; reference, 2.6-4.5 mg/dL).
  
  
  RESULTS
  Fractional excretion of phosphate was 34% (reference, <5% in the setting of hypophosphatemia), and plasma levels of FGF23 were highly elevated at 674 RU/mL (reference, <180 RU/mL). Immunohistochemical analysis of the patient's tumor showed strong staining for FGF23. Genetic analyses revealed a point mutation in the KRAS gene.
  
  
  CONCLUSIONS
  We present the first case in which a malignant neoplasm is documented to produce and secrete FGF23, leading to renal phosphate-wasting. Oncogenic osteomalacia should be considered in the differential diagnosis for patients with a malignant tumor who present with hypophosphatemia.
authors: Division of Renal Medicine, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts 02115, USA.
authors: David E
authors: DE
authors: Leaf
authors: Renata C
authors: RC
authors: Pereira
authors: Hasan
authors: H
authors: Bazari
authors: Harald
authors: H
authors: Jüppner
mesh_terms: D000230:Adenocarcinoma / Q000150:complications* / Q000235:genetics / Q000378:metabolism*; D000369:Aged, 80 and over; D003110:Colonic Neoplasms / Q000150:complications* / Q000235:genetics / Q000378:metabolism*; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D006801:Humans; D017674:Hypophosphatemia / Q000209:etiology / Q000378:metabolism; D010018:Osteomalacia / Q000209:etiology* / Q000378:metabolism; D010257:Paraneoplastic Syndromes / Q000209:etiology / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins / Q000235:genetics
chemical_list: C000717427:FGF23 protein, human; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
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