EWSR1 and acute lymphoblastic leukemia: Apart from its role in EWS, CD99 was found to be frequently overexpressed in several types of leukemia, including acute lymphoblastic leukemia (ALL) (Dworzak et al. 2004), acute myeloid leukemia (AML) and stem cells in myelodysplastic syndromes (MDS) (Chung et al. 2017).