Context: 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.
Design and intervention: 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.
Conclusion: 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.
© 2016 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license