A bcr3/Short Form PML-RARα Transcript in an Acute Promyelocytic Leukemia Resulted From a Derivative Chromosome 17 Due to Submicroscopic Insertion of the PML Gene Into the RARα Locus

Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia. Submicroscopic insertion of RAR alpha into PML, resulting in PML-RAR alpha from derivative chromosome 15, has been rarely reported. Herein, we describe a functional PML-RAR alpha transcript from the long arm of derivative chromosome 17 in a patient with microgranular APL. The conventional karyotype showed normal chromosomes 15 and 17. It is interesting that interphase and metaphase fluorescence in situ hybridizations demonstrated a fusion signal on the long arm of one chromosome 17 homolog, with both PML and RAR alpha still present on chromosomes 15 and 17, respectively, although the signal on one chromosome 15 was weaker, indicating partial loss of the PML gene. Reverse transcriptase-polymerase chain reaction revealed a transcript corresponding to a break cluster region 3 (bcr3) short form PML-RAR alpha. To the best of our knowledge, this is the first report of an APL with a bcr3 short form PML-RAR alpha transcript generated from derivative chromosome 17 due to submicroscopic insertion of the PML gene into the RAR alpha locus.