It is of note that RA has been used to dramatically improve clinical outcome in patients with acute promyelocytic leukemia (APL); where ninety-eight percent of patients with this disease carry a fusion of the PML and RARα genes that impairs the ability of RARα to induce hematopoietic stem/progenitor cell differentiation at physiological levels of RA [31, 32]. Here, PML is linked to acute promyelocytic leukemia.