It serves as a unique example of how one cytogenetic abnormality can define a distinct leukemia entity: t(8;21) leukemia is associated with a distinct morphology (i.e., relatively large blasts with a basophilic cytoplasm, azurophilic granules, and perinuclear clearing, presence of Auer rods), immunophenotype (i.e., frequent aberrant expression of CD19, PAX5, and CD56) and recurrent cooperating mutations including KIT, FLT3, KRAS, or NRAS, and both ASXL1 and ASXL2 [8]. The gene discussed is PAX5; the disease is leukemia.