CD99 and hemangiopericytoma: Histologically, SFT is composed of spindle cells with oval nuclei, typically arranged in “patternless” arrangement, separated by thin “strip-like” bundless of collagen.13 The tumor may have noticeable but varying degrees of vascularity, and focal areas of blood vessels with a stag horn branching pattern characteristic of hemangiopericytomas are often found.14 Immunohistochemistry, the tumor cells exhibit expression for vimentin, CD34, CD99, and Bcl-2, but no reactivity for cytokeratin, S-100 protein, actin, desmin, and calretinin.15,16