Fibroblast Growth Factor 23-Producing Phosphaturic Mesenchymal Tumor with Extraordinary Morphology Causing Oncogenic Osteomalacia

Abstract

A possible cause of hypophosphatemia is paraneoplastic secretion of fibroblast growth factor 23 (FGF-23). Tumors secreting FGF-23 are rare, mostly of mesenchymal origin, usually benign, and may be located anywhere in the body, including hands and feet, which are often not represented in conventional imaging. A 50-year-old woman presented with diffuse musculoskeletal pain and several fractures. Secondary causes of osteoporosis were excluded. Laboratory analysis revealed hypophosphatemia and elevated alkaline phosphatase, parathyroid hormone, and FGF-23. Thus, oncogenic osteomalacia due to neoplastic FGF-23 secretion was suspected. FDG-PET-CT and DOTATATE-PET-CT imaging demonstrated no tumor. Cranial MRI revealed a tumorous mass in the left cellulae ethmoidales. The tumor was resected and histopathological examination showed a cell-rich tumor with round to ovoid nuclei, sparse cytoplasm, and sparse matrix, resembling an olfactory neuroblastoma. Immunohistochemical analysis first led to diagnosis of olfactory neuroblastoma, which was later revised to phosphaturic mesenchymal tumor. Following the resection, FGF-23 and phosphate levels normalized. In conclusion, we here describe a patient with an FGF-23-secreting phosphaturic mesenchymal tumor with an unusual morphology. Furthermore, we emphasize diagnostic pitfalls when dealing with FGF-23-induced hypophosphatemia.

Clinical Applications of Somatostatin Receptor (Agonist) PET Tracers beyond Neuroendocrine Tumors

“…Small studies by Agrawal et al [ 46 ] and Jadhav et al [ 47 ] also reported higher sensitivity and specificity for SSTR tracers compared with [ 18 F]FDG. Multiple other case and small studies summarized in Table 2 report localization of culprit lesions in patients with TIO using SSTR tracers [ 14 , 38 , 39 , 40 , 41 , 42 , 44 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. An example showing culprit lesions identified in 3 patients using [ 68 Ga]Ga-DOTATATE PET-CT from a small study by John et al [ 38 ] is shown in Figure 5 .…”

Revisiting the WHO classification system of soft tissue tumours: emphasis on advanced magnetic resonance imaging sequences. Part 1

“…On MRI, HFLT presents as a soft tissue mass with indistinct margins, intralesional fat, and septations with local recurrence and occasionally blood products on GRE [ 32 ]. PMT, which is classified as a rarely metastasising lesion, is an extremely rare but clinically and histologically distinctive tumour that produces fibroblast growth factor 23, a hormone that blocks the reuptake of phosphate by proximal renal tubule, resulting in phosphaturia [ 33 ]. As such, PMTs produce phosphaturia and result in tumour-induced osteomalacia, which resolves with complete PMT excision [ 34 ].…”

“…As such, PMTs produce phosphaturia and result in tumour-induced osteomalacia, which resolves with complete PMT excision [ 34 ]. Clinically, the majority of patients with PMT exhibit elevated serum levels of fibroblast growth factor 23 [ 33 ]. PMTs tend to have a non-specific imaging appearance and can mimic TSGCT, and even ALT [ 35 ].…”