PML and acute promyelocytic leukemia: While pathogenesis of classic APL clearly involves RARA- and PML-dependent features, it is possible that pathogenesis of some APL-like syndromes associated with rare X-RARA fusions is more closely related to immortalization by RARA overexpression [159], possibly not even requiring homodimerization through partner X. Indeed, basal RARA expression is low and the translocations not only fuse two genes, but also put the downstream gene under the control of the upstream gene promoter.