Tumor induced osteomalacia secondary to anaplastic thyroid carcinoma: A case report and review of the literature.
BACKGROUND
Tumor induced osteomalacia related to anaplastic thyroid cancer has never been reported.


OBJECTIVE
We describe a case of tumor induced osteomalacia (TIO) in a patient with a fibroblast growth factor 23 (FGF-23) secreting anaplastic thyroid carcinoma. The current imaging modalities are reviewed.


METHODS
Clinical, biochemical, and radiological assessments were done, including computer tomography (CT) of the neck and skull to thigh positron emission tomography (PET)/CT. The patient underwent surgical tumor debulking three days after presentation due to airway compromise. Molecular studies of the resected tissue were performed using reverse transcriptase-polymerase chain reaction (RT-PCR) and gel electrophoresis for the phosphaturic mesenchymal tumor FGF-23.


RESULTS
Resected tissue demonstrated features of anaplastic thyroid cancer with positive markers for FGF-23 protein, consistent with a FGF-23 secreting paraneoplastic tumor. The patient's metastatic burden rapidly progressed as demonstrated by a dramatic rise in serum FGF-23 levels and worsening hypophosphatemia in concert with progression of the metastatic lesions on PET/CT.


CONCLUSIONS
We believe that our patient's rapidly progressive anaplastic thyroid cancer was responsible for persistent hypophosphatemia and osteomalacia, substantiated by the finding of FGF-23 protein within the thyroid tumor cells. Our case indicates that anaplastic thyroid cancer can cause TIO.
Division of Endocrinology, Mayo Clinic, Jacksonville, FL 32224, United States.
Ejigayehu G
EG
Abate
Division of Endocrinology, Mayo Clinic, Jacksonville, FL 32224, United States.
Victor
V
Bernet
Department of Pathology, Mayo Clinic, Jacksonville, FL 32224, United States.
Cherise
C
Cortese
Department of Radiology, Mayo Clinic, Jacksonville, FL 32224, United States.
Hillary W
HW
Garner
Anaplastic thyroid cancer; FGF 23; Hypophosphatemia; Osteomalacia; Tumor induced osteomalacia