- Leukocyte antigen CD34 is expressed by a subset of cultured endothelial cells and on endothelial abluminal microprocesses in the tumor stroma. Schlingemann, R.O., Rietveld, F.J., de Waal, R.M., Bradley, N.J., Skene, A.I., Davies, A.J., Greaves, M.F., Denekamp, J., Ruiter, D.J. Lab. Invest. (1990)