RUNX1 and acute lymphoblastic leukemia: The chromosomal translocation t(12;21)(p13;q22) is the most common structural variation of pediatric B cell precursor acute lymphoblastic leukemia (BCP‐ALL) and results in the fusion of the two hematopoietic transcription factors ETS translocation variant 6 (ETV6) and runt‐related transcription factor 1 (RUNX1).