Cryptic translocation of PML/RARA on 17q. A rare event in acute promyelocytic leukemia.

Cryptic translocations in acute promyelocytic leukemia are rare. Usually the gene fusion PML/RARA is located on chromosome 15. Combined cytogenetic, fluorescence in situ hybridization (FISH), and molecular (polymerase chain reaction [PCR]) analysis were employed for the diagnosis and precise localization of the fusion gene. Conventional cytogenetics showed a normal karyotype; PCR showed a typical PML/RARA rearrangement in exon 1. FISH analysis revealed that a submicroscopic part of chromosome 15 had been inserted into 17q. This case adds further information on alternative ways of rearrangement of the PML/RARA genes, possibly correlated with all-trans retinoic acid resistance.