CD34 and neoplasm: The problem of antigen specificity is highlighted by the detection of CD34 antigen on lymphatic vessels, perivascular stromal cells as well as other stromal elements while this is compounded by the absence of FVIII-RA on part of the capillary endothelium in tumour tissue (Holthofer et al, 1982; Parums et al, 1990; Traweek et al, 1991; Miettinen et al, 1994).