IKZF1 and acute lymphoblastic leukemia: Single copy losses affecting this gene occur at a frequency of around 9%, while BTG1 copy number losses appear to be enriched in specific cytogenetic subgroups, such as ETV6‐RUNX1, BCR‐ABL1, and BCR‐ABL1‐like positive BCP‐ALL, and co‐occur with genetic alterations affecting the B‐lineage determinants IKZF1 and PAX5 and the immune modulatory molecule BTLA (Kuiper et al., 2007; Mullighan et al., 2007; Roberts et al., 2014).