Acute promyelocytic leukemia with insertion of PML exon 7c: a novel variant transcript related to good prognosis that is not detected with real-time polymerase chain reaction

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) characterized by the specifi c chromosomal translocation t(15;17)(q22;q21), producing the PML – retinoic acid receptor α (RAR α ) fusion gene which contributes to APL pathogenesis and mediates the therapeutic response to all- trans retinoic acid (ATRA). Due to the diff erent PML breakpoints, three major PML – RAR α isoforms that cause diff erent clinical manifestations and therapeutic responses have been identifi ed: long or bcr1 (intron 6 PML), variant or bcr2 (exon 6 PML) and short or bcr3 (intron 3 PML) [1,2]. In addition to these isoforms, atypical PML – RAR α transcripts in patients with t(15;17) positive APL have been reported; these atypical transcripts may be undetected at diagnosis, and their clinical features and biological signifi cance remain unclear. Previous studies of atypical PML – RAR α variants have demonstrated that rare PML breakpoints downstream of intron 6 are potentially associated with an aggressive course of disease and adverse prognosis [3 – 5]. In this study, we report a novel PML – RAR α variant with insertion of PML exon 7c in a patient with APL with good clinical outcome.