CD34 is a transmembrane glycoprotein with a molecular mass of approximately 110 kD that is selectively expressed on human hematopoietic progenitor cells, endothelial cells and some fibroblasts. It could act as a scaffold for the attachment of lineage specific glycans, allowing stem cells to bind to lectins expressed by stromal cells or other marrow components. CD34 is highly expressed on hematopoietic progenitors, as well as on endothelial cells. CD34 has been used to measure angiogenesis, which reportedly predicts tumor recurrence.