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PHOSPHATURIC MESENCHYMAL TUMOUR – A CASE REPORT

Aim: To describe a case of phosphaturic mesenchymal tumour and advances in the immunohistochemical diagnosis. Case: A 36-year-old male presented with progressive fatigue, localised right back pain with movement and bilateral foot pain 7 months following trivial injury over the 7th rib anteriorly while playing rugby. A trial of prednisone was ineffective. Results: Biochemistry showed severe hypophosphataemia, urinary phosphate loss, raised alkaline phosphatase, mildly reduced serum calcium and magnesium and normal electrolytes. Sestamibi scan with CT scanning highlighted an area of increased uptake in the right C7 transverse process. Serum analysis showed fibroblast growth factor-23 secreting hormone. Histology showed bland cells with densely granular and eosinophilic background. No osteoclast-like giant cells, calcified matrix, haemorrhage or necrosis was identified. Immunohistochemistry showed tumour cells positive for CD56 and negative for synaptophysin, chromagranin, TTF-1, CD31 and Ki -67. Slides referred to Dr Anthony Gill, Royal North Shore Hospital, Sydney, showed strong positivity to FGF23 and diffuse strong positivity to somatostatin receptor 2A. Discussion: Phosphaturic mesenchymal tumour is a rare phosphate wasting tumour associated with oncogenic osteomalacia. They have been erroneously diagnosed as other mesenchymal tumours including hemangiopericytoma and osteosarcoma. Expression of FGF23 and SSTR2A are diagnostic.