A neuroendocrine cause of oncogenic osteomalacia.

All definite cases of oncogenic osteomalacia have, until now, been classified as mesenchymal tumours. We report here a case of oncogenic osteomalacia caused by a spinal tumour. Microscopically, it resembled the mixed connective tissue variant of previously described phosphaturic tumours. Immunohistochemical studies, however, showed the tumour cells to be positive for low molecular weight cytokeratin (CAM 5.2), S100 protein, PGP 9.5, and synaptophysin. Electron microscopy demonstrated neurosecretory granules. The histopathological findings strongly suggest that this is a neuroendocrine tumour.