PBX1 and precursor B-cell acute lymphoblastic leukemia: The gene fusions BCR‐ABL1, TCF3‐PBX1, and ETV6‐RUNX1 are recurrent in B‐cell acute lymphoblastic leukemia (B‐ALL) and are found with low frequency in coexistence with CRLF2 (cytokine receptor‐like factor 2) rearrangements and overexpression.