Does tumour-induced osteomalacia occur in dogs?

Tumour-induced osteomalacia of humans is a renal phosphate-wasting syndrome associated with slow-growing mesenchymal tumours. Seventy to eighty percent of these tumours are classified as phosphaturic mesenchymal tumours of mixed connective tissue, that strongly resemble haemangiopericytomas. Affected individuals develop osteomalacia, with bone and muscle pain, hypophosphataemia, and inappropriately low concentrations of 1,25-dihydoxyvitamin D. Surgical removal of the tumour leads to resolution of these clinical signs. These tumours over-express factors known as ‘phosphatonins’, that lead to phosphate-wasting through the kidney, and suppression of renal 1α-hydroxylase. The most important and most researched of these are fibroblast growth factor-23 (FGF23), matrix extracellular phosphoglycoprotein (MEPE), and secreted frizzled-related protein- 4 (sFRP4). In-situ hybridisation, immunohistochemistry, and PCR have shown FGF23 protein and mRNA present in tumour cells of these mesenchymal tumours. Research into this syndrome has uncovered the role of these substances, and others, in the normal physiology of phosphorous homeostasis. Haemangiopericytoma is a common tumour of dogs, but no work has been performed examining the possibility of over-expression of phosphatonin, and tumour-induced osteomalacia in these animals. A study is underway to determine if haemangiopericytomas, and other mesenchymal tumours of dogs, produce FGF23, MEPE or sFRP4.