A still open and controversial point concerns the role of CD38 in acute promyelocytic leukemia (APL), the M3 subtype of AML, which is characterized by the presence of the chimeric gene promyelocytic leukemia-retinoic acid receptor α (PML-RARA) (123) and by an arrest of leukocyte differentiation at the promyelocyte stage. The gene discussed is RARA; the disease is acute promyelocytic leukemia.