This study demonstrates that the frequency of RARA-PML expression has been underestimated and highlights remarkable complexity at chromosomal breakpoint regions in APL even in cases with an apparently simple balanced t(15;17)(q24;q12)..     ///    "Six patients were falsely classified as RARA-PML negative due to deletions on chromosome 15 and/or 17, or alternative splicing leading to atypical RARA-PML fusion transcripts, which were not identified by conventional RT-PCR assays. "    ///    " Reciprocal RARA-PML transcripts are not detected in approximately 25% of patients with PML-RARA positive acute promyelocytic leukemia (APL), but the reasons for this are poorly understood. "    ///    "Atypical mRNA fusions in PML-RARA positive, RARA-PML negative acute promyelocytic leukemia.. "    ///    We studied 21 PML-RARA positive/RARA-PML negative cases by bubble PCR and multiplex long template PCR to identify the genomic breakpoints.     ///    Three cases were found to have complex rearrangements involving a third locus: the first had a PML-CDC6-RARA forward DNA fusion and expressed a chimeric PML-CDC6-RARA mRNA in addition to a PML-RARA. 