CD34 antibody antigen is selectively expressed in human lymphoid and myeloid hematopoietic progenitor cells. Studies have shown the CD34 antibody also reacts with vascular endothelial cells in normal tissues and in benign and malignant proliferations. The utility of CD34 is in the study of benign and malignant vascular tumors as well as characterization of acute leukemia in bone marrow. CD34 has been used to measure angiogenesis in many types of tumors, which reportedly predicts tumor recurrence. It is also useful to aid the differentiation of dermatofibrosarcoma protuberans from fibrous histiocytoma.