sentences:  Phosphaturic mesenchymal tumors is characterized by a hypervascular proliferation of apparently non-malignant spindled cells associated with a variable amount of ‘smudgy’ calcified matrix but a small subset of these tumors exhibit malignant histological features and may behave in a clinically malignant fashion.In a series of 15 patients with this disease, 9 were found to have tumors that bore fusions between the "FGFR1" gene and the FN1 gene located on human chromosome 2 at position q35.The "FGFR1-FN1" fusion gene was again identified in 16 of 39 (41%) patients with phosphaturic mesenchymal tumors.