[Ostemalacia due to a tumor secreting FGF-23]

A case of oncogenic osteomalacia in a 50-year-old male is here presented. He suffered severe bone pain and marked muscular weakness of 4 years' duration. There were several vertebral deformities in the thoracic spine, bilateral fractures of the iliopubic branches, another fracture in the left ischiopubic branch, and a Looser's zone in the right proximal tibia. An octreotide-Tc scan allowed to identify a small tumor in the posterior aspect of the right knee. It was surgically removed. Microscopically, it was a phosphaturic mesenchymal tumor-mixed connective tissue (PMT-MCT). Expression of FGF-23 was documented by immune-peroxidase staining. There was rapid improvement, with consolidation of the pelvic fractures and the tibial pseudo-fracture. The laboratory values returned to normal.