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

Acute Promyelocytic Leukemia with Rare Genetic Aberrations: A Report of Three Cases

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML) that is characterized by the PML::RARA fusion or, more rarely, a variant RARA translocation. While APL can be clinically suspected, diagnosis of APL requires genetic confirmation. Targeted therapy such as all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO) has dramatically improved the prognosis of APL patients, but this is dependent on timely genetic testing as different fusions and/or mutations can affect therapeutic outcomes. Here we report three APL cases with various genetic aberrations: cryptic PML::RARA fusion, variant RARA rearrangement, and typical PML::RARA fusion with co-existing FLT3-ITD mutation. They serve to illustrate the utility of integrating genetic testing, using chromosome analysis, fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR), and next-generation sequencing (NGS) in providing a detailed understanding of the genetic alterations underlying each patient's disease.

An Atypical PML-RARA Rearrangement Resulting from Submicroscopic Insertion of the RARA Gene at the PML Locus with Novel Breakpoints within PML Exon 7b and RARA Exon 3

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-RARArearrangements. 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 PMLIIa (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.

A Paediatric Acute Promyelocytic Leukaemia Patient Harbouring a Cryptic PML-RARA Insertion due to a Complex Structural Chromosome 17 Rearrangement

Acute promyelocytic leukaemia with PML-RARA fusion is usually associated with the t(15;17)(q24.1;q21.1) translocation but may also arise from complex or cryptic rearrangements. The fusion usually resides on chromosome 15 but occasionally on others. We describe a cryptic PML-RARA fusion within a novel chromosome 17 rearrangement. We performed interphase fluorescence in situ hybridisation (FISH) using a dual-fusion PML-RARA probe, followed by reverse transcriptase-polymerase chain reaction (RT-PCR) for PML-RARA, karyotyping, and metaphase FISH using RARA break-apart, locus-specific, and subtelomere probes for chromosome 17. An 850K SNP microarray was also employed. Interphase and metaphase FISH showed atypical results involving a single PML-RARA fusion, no second fusion, but instead separate diminished PML and RARA signals. RT-PCR confirmed PML-RARA fusion; however, karyotyping detected only an altered chromosome 17. Metaphase FISH showed the single fusion and diminished 5' RARA signals located unexpectedly in the subtelomeric short-arm and long-arm regions of the rearranged chromosome 17, respectively. SNP microarray revealed no copy number abnormality. This paediatric patient with PML-RARA fusion reflects a cryptic insertion that resides within a complex and novel chromosome 17 rearrangement. This rearrangement likely arose via 7 chromosome breaks with the insertion occurring first followed by sequential paracentric and then pericentric inversions.

Acute promyelocytic leukemia with the translocation t(15;17)(q22;q21) associated with t(1;2)(q42~43;q11.2~12): a case report

Background

Acute promyelocytic leukemia is characterized by a typical reciprocal translocation t(15;17)(q22;q21). Additional chromosomal abnormalities are reported in only 23–43 % of cases of acute promyelocytic leukemia.

Case presentation

Here we report the case of a 46-year-old Syrian Alawis woman with acute promyelocytic leukemia with the typical t(15;17) translocation, but with a second clone presenting a t(1;2)(q42~43;q11.2~12) translocation as an additional abnormality. To the best of our knowledge, an association between these chromosomal abnormalities has not previously been described in the literature. Our patient started treatment with all-trans retinoic acid 10 days after diagnosis but died the same day of treatment initiation due to hemolysis, intracranial hemorrhage, thrombocytopenia, and disseminated intravascular coagulation.

Conclusion

The here reported combination of aberrations in a case of acute promyelocytic leukemia seems to indicate an adverse prognosis, and possibly shows that all-trans retinoic acid treatment may be contraindicated in such cases.

A rare case with typical acute promyelocytic leukemia morphology associated with isolated isochromosome 17q without RARα rearrangement

Isolated isochromosome 17q has rarely been reported in hematologic tumor patients. A 37-year-old man was admitted with fever and weakness. Blood routine test showed anemia and thrombocytopenia. The morphology and immunology of bone marrow cells conform to classic acute promyelocytic leukemia (APL). But the karyotype showed isolated isochromosome 17q without t(15;17) (q22;q12). Rverse transcriptase polymerase chain reaction (RT-PCR) for PML -RARa was negative and fluorescence in situ hybridization (FISH) analysis showed no RARa gene rearrangements.The patient responded poorly to all trans retinoic acid and traditional chemotherapy with daunorubicin and cytarabine and survived only 43 days after diagnosis. The pathogenesis and the best treatment choice for this kind of patients are not clear currently.

Masked t(15;17) APL with the insertion of PML-RARalpha fusion gene in 4q21

Most cases of acute promyelocytic leukemia (APL) are characterized by the reciprocal translocation t(15;17); however, several complex variant translocations have also been reported. Here we report complex cytogenetic abnormalities without t(15;17) assayed by the G-banding method in a 62-year-old woman with the typical morphology and clinical features of APL. Based on spectral karyotyping and FISH analyses, we confirm the insertion of a cryptic chromosomal segment containing the PML/RARalpha fusion gene. The patient achieved complete remission after treatment with all-trans retinoic acid (ATRA) alone. Although the mechanism of this cryptic variant insertion is not known, we conclude that the insertion of PML-RARalpha fusion into 4q21 seems not to alter the effectiveness of treatment with ATRA.

A new three-way variant t(15;22;17)(q22;q11.2;q21) in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by the t(15;17)(q22;q21), which results in the fusion of the promyelocytic leukemia (PML) gene at 15q22 with the retinoic acid alpha-receptor (RARA) at 17q21. We report the case of a 44-year-old man with APL carrying a new complex variant translocation (15;22;17). Karyotypic analysis with G-banding of bone marrow cells revealed t(15;22;17) (q22;q11.2;q21). Fluorescence in situ hybridization with a PML/RARA dual-color DNA probe showed the fusion signals. RT-PCR analysis showed long-form PML/RARA fusion transcripts. A complete remission was attained with a course of conventional chemotherapy with all-trans retinoic acid (ATRA). This is the first report of a new three-way translocation of 22q11 involvement with APL.

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.

Acute promyelocytic leukemia and constitutional trisomy 21

The incidence of acute myelogenous leukemia (AML) in patients with constitutional trisomy 21 is estimated to be 1 in 300; it is usually seen before age four. Clinical and epidemiological data confirm the improved life expectancy of patients with Down syndrome and their increased susceptibility to the development of leukemia, among other cancers. The most frequent subtype of AML associated with Down syndrome is acute megakaryoblastic leukemia (FAB: M7). The description of acute promyelocytic leukemia (APL) in adult patients with Down syndrome is exceedingly rare. Herein, we describe the unusual presentation, treatment, results, and clinical course of an adult patient with APL and constitutional trisomy 21 and provide a brief review of the literature.

A new variant t(6;15;17)(q25;q22;q21) in acute promyelocytic leukemia: fluorescence in situ hybridization confirmation

Acute promyelocytic leukemia (APL) is characterized by the t(15;17)(q22;q21), which results in the fusion of the promyelocytic leukemia (PML) gene at 15q22 with the retinoic acid alpha-receptor (RARalpha) at 17q21. The 2 chimeric genes PML/RARalpha and RARalpha/PML are thought to play a role in leukemogenesis. We report a case of APL in a patient carrying an apparently complex variant translocation identified as t(6;15;17) by R-banding and whole chromosome 15 and 17 painting. However, FISH analysis with a PML/RARalpha dual-color kit showed a more complex translocation, resulting presumably from a two-step rearrangement, with PML-RARalpha fusion gene located as expected on the der(15) but the residual 5'-RARalpha signal located on the der(6). The patient achieved complete remission with all-trans retinoic acid treatment associated with chemotherapy. This case illustrates the usefulness of combined cytogenetics, FISH, and molecular biology to evidence the PML/RARalpha fusion gene in complex cases.