Identification of PML-RARA rearrangement by RT-PCR and sequencing in an acute promyelocytic leukemia without t(15;17) on G-banding and FISH.

Acute promyelocytic leukemia (APL) is characterized by a reciprocal translocation, t(15;17) (q22;q12), resulting in fusion of the genes promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARA). With conventional cytogenetic methods, these translocations are detected in about 70-90% of patients, with most of the negative results due to technical problems or cryptic variants. Those masked PML-RARA fusions can be identified by molecular analyses such as reverse transcriptase-polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH). We have studied a patient showing morphological, cytochemical, and immunophenotypic features of hypergranular APL with trisomy 8 as a sole anomaly. t(15;17) was not evident on FISH tests, while RT-PCR and cDNA sequencing revealed the presence of PML-RARA transcripts.