CD34 is a heavily glycosylated type I transmembrane molecule, that can be phoshorylated by a variety of kinases including Protein kinase C and Tyrosine kinases. CD34 antigen is expressed on small vessel endothelial cells and tumors of epithelial origin. CD34 is possibly an adhesion molecule with a putative role in early hematopoiesis by mediating the attachment of stem cells to the bone marrow extracellular matrix or directly to stromal cells. 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. So CD34 is considered to be ideal marker for identifying and quantifying hematopoietic progenitor stem cells. With interaction with CrkL, CD34 becomes a substrate for PKC and CD34 surface expression is associated with activation of PKC.