Acute promyelocytic leukemia with apparently normal karyotype: molecular findings and response to all-trans retinoic acid.

Acute promyelocytic leukemia (APL) is specifically associated with a reciprocal translocation, t(15; 17)(q22; q21), leading to the formation of a fusion of the retinoic acid receptor-alpha (RARA) gene and the promyelocytic leukemia (PML) gene. However, there are several reports describing APL cases lacking the t(15; 17). Many such cases are those bearing variant translocations involving chromosomes 15 or 17, and those with no chromosomal aberrations have rarely been reported. We have studied a patient with APL showing an apparently normal karyotype which was confirmed by spectral karyotyping (SKY). A submicroscopic PML-RARA fusion was identified by reverse transcriptase-polymerase chain reaction (RT-PCR) and fluorescent in situ hybridization (FISH). All-trans retinoic acid (ATRA) was effective as the initial therapy for remission induction and as the reinduction therapy after a relapse. The present study shows the key role of the fusion of PML-RARA in the responsiveness to ATRA as well as in the leukemogenesis of APL.