Histopathology of the tumor. (a) The tumor was composed of sheet-like proliferation of uniform oval-shaped tumor cells in a fibrous background with prominent capillary-sized vessels. (b) The tumor was focally positive for FGF23 with a punctate perinuclear staining pattern, while blood vessels were negative. (c) Soft tissue invasion of the tumor cells. (d) Intracortical invasion of the tumor cells.