The diagnostic hallmark of acute promyelocytic leukemia (APL) is the reciprocal translocation t(15;17), resulting in the characteristic PML-RARA fusion; however, patients occasionally have masked PML-RARA rearrangements. We report an APL case with no evidence of t(15;17) or PML-RARA rearrangement by karyotype or commercial reverse transcription polymerase chain reaction analyses. Fluorescence in situ hybridization detected a small RARA insertion signal within PML. mRNA sequencing identified a novel PML-RARA transcript generated from the juxtaposition of PML IIa (exons 1–4, 6, and 7ab) and RARA exons (3–9), with novel breakpoints in PML exon 7b and RARA exon 3. The patient achieved molecular remission after the second consolidation chemotherapy and remains in complete remission 22 months after initial presentation. This is the first report of an APL case presenting with submicroscopic ins(15;17) and simultaneous novel breakpoints in both PML and RARA. This case highlights the importance of sequence analysis to confirm APL diagnosis and for subsequent monitoring of minimal residual disease.

Keywords:
Acute promyelocytic leukemia variant, Cryptic PML-RARA, ins(15;17), Breakpoint cluster region
© 2019 S. Karger AG, Basel
2019
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