Patients with BPDCN were divided into three groups according to the maturational stage of the blast/tumor cells as defined by the pattern of expression of CD34 and CD117: 1) immature blastic pDC neoplasms (8/46 cases; 17%) showed expression of CD34 in at least a fraction of the blast cells; 2) intermediate blastic pDC neoplasms (24/46 patients; 52%) typically displayed partial positivity for CD117 in the absence of CD34 expression on the blast cells, and; 3) mature cases (14/46 cases; 30%) had a CD34− CD117− tumor pDC immunophenotype. This evidence concerns the gene CD34 and neoplasm.