[55] Frequent Expression of Fibroblast Growth Factor-23 (FGF-23) mRNA in Aneurysmal Bone Cyst (ABC).

Smita Krishnamurthy, Carrie Y Inwards, Andre M Oliveira, Andrew L Folpe. Mayo Clinic, Rochester, MN

Background: The great majority of cases of tumor-induced osteomalacia (TIO) are caused by a morphologically distinctive soft tissue and bone tumor, known as phosphaturic mesenchymal tumor, mixed connective tissue type (PMT). In almost all instances PMT produce TIO through secretion of FGF-23, a phosphaturic hormone. We have previously shown detection of FGF-23 by RT-PCR in formalin-fixed, paraffin-embedded (FFPE) tissues to be a valuable adjunct to this sometimes difficult diagnosis. However, TIO caused by other mesenchymal tumors (e.g., polyostotic fibrous dysplasia) is well documented, suggesting that FGF-23 expression may not be unique to PMT. Prompted by our earlier findings of FGF-23 expression in 1 ABC and 1 chondromyxoid fibroma (CMF) of flat bone type, we examined a larger series of ABC and CMF for FGF-23 expression.
Design: FFPE blocks from 13 cases with typical morphologic and radiographic features of ABC (8) and CMF (5) were retrieved from our archives. The clinical records of all patients were reviewed. RT-PCR for FGF-23 was performed using our previously published methods.
Results: The 13 tumors studied occurred in 8 men and 5 women ranging in age from 8 to 75 years (mean, 27 yrs). All of the tumors involved bone, including 2 in the skull, 4 in the spine, 2 in the upper extremity (1 each in metacarpal and ulna), 3 in the lower extremity (2 in tibia and 1 in acetabulum), and 1 each in the rib and clavicle. None of the patients had evidence of TIO in the clinical records. One ABC and 2 CMF did not contain amplifiable mRNA and were excluded. RT-PCR for FGF-23 was positive in 4/7 (57%) of the ABCs. None of the CMF were positive.
Conclusions: The results of the present study confirm and amplify our previous finding of FGF-23 expression in a subset of ABCs, all with typical clinical, radiographic and morphologic features, and without any features suggestive of PMT. This finding is intriguing, inasmuch as calcified matrix resembling that seen in many PMT is often identified in ABC. It is unclear whether FGF-23 expression is related to the distinctive morphologic features of ABC, or is simply an epiphenomenon. Most importantly, these findings emphasize that the diagnosis of PMT, as with any diagnosis, must rest on an integration of all clinical, radiographic and laboratory findings, and must not rely on FGF-23 studies alone.
Category: Bone & Soft Tissue

Tuesday, March 1, 2011 1:45 PM

Platform Session: Section E, Tuesday Afternoon


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