PAX5 and acute lymphoblastic leukemia: In more than 80% of cases of this so-called Ph-like ALL, the variant possesses deletions in key transcription factors involved in B-cell development including IKAROS family zinc finger 1 (IKZF1), transcription factor 3 (E2A), early B-cell factor 1 (EBF1) and paired box 5 (PAX5).12 Similarly, kinase-activating mutations are seen in 90% of the Ph-like ALL.