PSMB5 and acute promyelocytic leukemia: Ninety-seven percent of acute promyelocytic leukemia (APL) patients harbor the t(15;17) mutation, and less than 2% harbor the t(11;17) mutation, which leads to the formation of chimeric genes that encode the PML/RARα and PLZF/RARα (X-RARα) fusion proteins.