CD34 and precursor B-cell acute lymphoblastic leukemia: “Stem/B” cells are more quiescent and less actively cycling than leukemic “Pro-B” cells, highlighting the importance and feasibility of tracking rare but distinct leukemia cell populations in patients undergoing therapy.[19] Obro et al[3] reported that the subpopulations are most commonly characterized by a bimodal expression of CD34 in childhood B-ALL patients.