PAX5 and leukemia: In accordance, the Sigvardsson laboratory described similar development of pre-B leukemia in a subset of Ebf1+/–Pax5+/–mice with high molecular heterogeneity between tumors.23 Based on cell surface marker expression and analysis of transcripts of various B-cell and stage-specific factors, it appears pre-B tumors derived from EB mice display similar molecular heterogeneity.