CD34 is a cell surface glycophosphoprotein that is expressed on human hematopoietic progenitor cells and can be used to identify blasts. CD34 is a marker for vascular endothelial cells and has been shown in the literature to be highly sensitive for angiosarcoma and Kaposi’s sarcoma. In addition, CD34 is expressed in soft tissue tumors such as gastrointestinal stromal tumors (GIST). It is also used to differentiate solitary fibrous tumors, dermatofibrosarcoma protuberans and malignant phyllodes tumors of the breast.