Differentiation therapy with ATRA for acute promyelocytic leukemia (APL) serves as a pivotal example for targeting transcriptional addiction due to the retinoic acid receptor alpha (RARA) fusion with a second gene (PML) specifying a novel Krüppel-like zinc finger protein, but also as an example explaining leukemia tissue editing by differentiation induction (20, 110). The gene discussed is RARA; the disease is acute promyelocytic leukemia.