case_images: PMC11631047_01
case_images: (A) CT image of right iliac lesion with cortical destruction (white arrow). (B) PET/CT image, revealing right iliac FDG-avid lesion (white arrow). (C) PET/CT image, revealing L4 vertebral lesion (white arrow). (D) PET/CT image, revealing left supra-acetabular area lesion (white arrow). (E) Repeat-biopsy sample of the right iliac lesion, revealing a spindle and epithelioid mesenchymal neoplasm in a myxoid background. (F) Biopsy sample of left supra-acetabular lesion, revealing fibrous dysplasia. Abbreviation: FDG, fluorodeoxyglucose.
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case_images: The urologist performed CT urogram when 2 lytic bone lesions:a right iliac lesion (4.3 x 1.5 cm) with cortical destruction (Figure 1A), and another L4 vertebral body lesion of 1.5 cm:were discovered. The PET/CT revealed 2 more FDG-avid lesions: one in the left supra-acetabular area and another in the L4 vertebral body, raising the possibility of metastatic disease (Figure 1B-D). The orthopedic team at our hospital repeated biopsy of the right iliac lesion which confirmed the presence of myxoid spindle-cell tumor, histologically compatible with phosphaturic mesenchymal tumor (PMT) (Figure 1E). During the same procedure, biopsy and cryoablation of the left supra-acetabular lesion were also performed; the histopathologic findings of this lesion showed, unexpectedly, fibrous dysplasia (FD) (Figure 1F).
case_images: Bone density changes over 2 yr following cryoablation of PMT and FD. Abbreviations: FD, fibrous dysplasia; PMT, phosphaturic mesenchymal tumor.
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case_images: His BMD revealed significant osteoporosis and on subsequent BMD assessment, without any anti-osteoporosis medication, his BMD improved significantly as shown in Figure 2.
case_images: (A) Mutually exclusive fusion of genes FN1::FGF1 or FN1::FGFR1 causes excess FGF23 production. The FGF23 molecules are protected by phosphorylation and lysis, by excess GALNT3 expression which helps keep the molecules in intact form. (B) GNAS mutation increases cAMP activity leading to increased production of FGF23 molecules. However, decreased activity of GALNT3 and increased activity of FAM20C increases phosphorylation of the molecules, making them susceptible to lysis by FURIN.
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case_images: Effectively, this increases the number of intact molecules and hence results in an elevated intact FGF23: total FGF23 ratio (Figure 3A). As a result, the intact FGF23: total FGF23 ratio is low (Figure 3B), and hence, despite elevated FGF23 production in FD, classic phosphaturia and osteomalacia are not typically seen.
case_images: (A) FGF23 mRNA chromogenic in situ hybridization of PMT. (B) FGF23 mRNA chromogenic in situ hybridization of FD. Abbreviations: FD, fibrous dysplasia; PMT, phosphaturic mesenchymal tumor.
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case_images: The results were strongly positive in PMT (Figure 4A) and negative in FD (Figure 4B), indicating that FGF23 was overproduced by the PMT but not by the FD.
case_images: Line graph showing changes in total FGF23 and serum phosphorus levels from before cryoablation to subsequent follow ups.
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case_images: After about a year following cryoablation, the patient's total FGF23 level had trended up from 102 to 142 RU/mL with unchanged phosphorus and ALP levels:both of which had normalized since cryoablation (Table 2 and Figure 5).