NB4 cells are derived from an APL patient, and express a bcr1 PML::RARA mRNA from a classical t(15;17) translocation; however, these cells also have TP53 mutations and are aneuploid (both are extremely rare in primary APL samples and probably acquired during immortalization) (60, , –63). This evidence concerns the gene TP53 and acute promyelocytic leukemia.