PML::RARA and GATA2 proteins interact via DNA templates to induce aberrant self-renewal in mouse and human hematopoietic cells.

The underlying mechanism(s) by which the PML::RARA fusion protein initiates acute promyelocytic leukemia is not yet clear. We defined the genomic binding sites of PML::RARA in primary mouse and human hematopoietic progenitor cells with V5-tagged PML::RARA, using anti-V5-PML::RARA chromatin immunoprecipitation sequencing and CUT&RUN approaches. Most genomic PML::RARA binding sites were found in regions that were already chromatin-accessible (defined by ATAC-seq) in unmanipulated, wild-type promyelocytes, suggesting that these regions are "open" prior to PML::RARA expression. We found that GATA binding motifs, and the direct binding of the chromatin "pioneering factor" GATA2, were significantly enriched near PML::RARA binding sites. Proximity labeling studies revealed that PML::RARA interacts with ~250 proteins in primary mouse hematopoietic cells; GATA2 and 33 others require PML::RARA binding to DNA for the interaction to occur, suggesting that binding to their cognate DNA target motifs may stabilize their interactions. In the absence of PML::RARA, Gata2 overexpression induces many of the same epigenetic and transcriptional changes as PML::RARA. These findings suggested that PML::RARA may indirectly initiate its transcriptional program by activating Gata2 expression: Indeed, we demonstrated that inactivation of Gata2 prior to PML::RARA expression prevented its ability to induce self-renewal. These data suggested that GATA2 binding creates accessible chromatin regions enriched for both GATA and Retinoic Acid Receptor Element motifs, where GATA2 and PML::RARA can potentially bind and interact with each other. In turn, PML::RARA binding to DNA promotes a feed-forward transcriptional program by positively regulating Gata2 expression. Gata2 may therefore be required for PML::RARA to establish its transcriptional program.

Identification of a novel fusion gene, RARA::ANKRD34C, in acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a specific subtype of acute myeloid leukemia that is distinguished by the chromosomal translocation t(15;17)(q24;q21), which leads to the fusion of the promyelocytic leukemia (PML) gene with the retinoic acid receptor alpha (RARA). Recently, we identified a novel fusion gene in APL, RARA::ankyrin repeat domain 34C (ANKRD34C), identified its functions by morphological, cytogenetic, molecular biological and multiplex fluorescence in situ hybridization analyses, and demonstrated the potential therapeutic effect clinically and experimentally of all-trans retinoic acid (ATRA); the findings have important implications for the diagnosis and treatment of atypical APL.

Cytogenetically Cryptic Acute Promyelocytic Leukemia: A Diagnostic Challenge.

Cytogenetically cryptic acute promyelocytic leukemia (APL) is rare, characterized by typical clinical and morphological features, but lacks t(15;17)(q24;q21)/PML::RARA translocation seen in conventional karyotyping or FISH. The prompt diagnosis and treatment of APL are critical due to life-threatening complications associated with this disease. However, cryptic APL cases remain a diagnostic challenge that could mislead the appropriate treatment. We describe four cryptic APL cases and review reported cases in the literature. Reverse transcriptase polymerase chain reaction (RT-PCR) is the most efficient diagnostic modality to detect these cases, and alternative methods are also discussed. This study highlights the importance of using parallel testing methods to diagnose cryptic APL cases accurately and effectively.

Typical, atypical and cryptic t(15;17)(q24;q21) (PML::RARA) observed in acute promyelocytic leukemia: A retrospective review of 831 patients with concurrent chromosome and PML::RARA dual-color dual-fusion FISH studies.

The diagnosis of acute promyelocytic leukemia (APL) relies on the identification of PML::RARA fusion. While the majority of APL cases harbor a typical t(15;17)(q24;q21), atypical genetic mechanisms leading to the oncogenic PML::RARA fusion have been reported yet their frequency and scope remain poorly characterized. We assessed the genetic findings of 831 cases with APL investigated with concurrent chromosome banding analysis and dual-color dual-fusion fluorescence in situ hybridization (D-FISH) analysis at our institution over an 18.5-year timeframe. Seven hundred twenty-three (87%) cases had a typical balanced t(15;17) with both testing modalities. Atypical karyotypic results including complex translocations, unbalanced rearrangements and insertional events occurred in 50 (6%) cases, while 6 (0.7%) cases were cryptic by conventional chromosome studies despite PML::RARA fusion by D-FISH evaluation. Atypical FISH patterns were observed in 48 (6%) cases despite apparently balanced t(15;17) on chromosome banding analysis. Two hundred fifty (30%) cases displayed additional chromosome abnormalities of which trisomy/tetrasomy 8 (37%), del(7q)/add(7q) (12%), and del(9q) (7%) were most frequent. Complex and very complex karyotypes were observed in 81 (10%) and 34 (4%) cases, respectively. In addition, 4 (0.5%) cases presented as an apparently doubled, near-tetraploid stemline clone. This report provides the largest appraisal of cytogenetic findings in APL with conventional chromosome and PML::RARA D-FISH analysis. By characterizing the frequency and breadth of typical and atypical results through the lens of these cytogenetic testing modalities, this study serves as a pragmatic source of information for those involved in the investigation of APL in both the clinical and research laboratory settings.

[Diagnostic efficacy of WT1 expression in asymptomatic acute promyelocytic leukemia].

We report a case of early asymptomatic acute promyelocytic leukemia (APL) with leukopenia as the only hematologic abnormality. A 55-year-old woman was referred to our hospital with leukopenia (white blood cell [WBC] count of 1,500/µl with 36% neutrophils), which was incidentally determined during an annual medical checkup. Two months before the presentation, her WBC was 3,400/µl with 60% neutrophils. A WBC count was 1,200/µl with 40% neutrophils. Immature myeloid cells were not observed. Her hemoglobin level and platelet count were normal. Moreover, no clinical or laboratory evidence was suggestive of disseminated intravascular coagulation or infection. The peripheral blood WT1 mRNA level was increased to 26,000 copies/µg RNA. The bone marrow aspirate smear revealed 40% myeloperoxidase-positive promyelocytes with occasional Auer rods and faggots; however, circulating leukemia cells were not revealed by cell morphology or flow cytometry analysis. Quantitative reverse-transcription polymerase chain reaction analysis revealed WT1 and PML-RARA fusion transcripts in both the peripheral blood and bone marrow samples. Thus, the determination of peripheral blood WT1 expression may be sufficiently sensitive for detecting a small number of circulating APL cells.

Identification of a novel TNRC18-RARA fusion in acute promyelocytic leukemia lacking t(15;17)(q24;q12)/PML-RARA.

Acute promyelocytic leukemia (APL) is a unique disease entity in acute myeloid leukemia, characterized by PML-RARA fusion gene, which is generated by chromosomal translocation t(15;17)(q24;q21). We identified TNRC18-RARA as novel RARA fusion in resembling APL. Our study highlights the importance of combining multiple molecular techniques to characterize and optimally manage APL lacking classic t(15;17)(q24;q12)/PML-RARA fusion.

Preleukemic fusion genes typical for acute myeloid leukemia.

Acute myeloid leukemia (AML) is a highly heterogeneous subtype of leukemia, accounting for 25 % of childhood leukemias. By the presence of genetic mutations in hematopoietic/ progenitor stem cells, the bone marrow produces a large number of abnormal undifferentiated leukocytes (blasts), which significantly impairs the proper differentiation of cells. AML is induced by two interventions. Chromosomal translocation during hematopoiesis of intrauterine development is the first intervention. This creates preleukemic fusion genes (PFG), which can later be transformed by a second intervention (point genetic mutation - deletion, insertion ) into a functional malignant clone. Characteristic AML fusion genes include AML1-ETO, PML-RARA or MLL-AF9, which in turn produce hybrid proteins with altered function. Several studies suggest that these PFGs are considered an important prognostic tool in disease assessment. While the incidence of PFG characteristic of acute lymphoblastic leukemia (ALL) has been relatively well studied by several research groups and has been estimated at 1 to 5% in the umbilical cord blood of healthy neonates, PFG relevant to AML are still not sufficiently clarified.

Report of a new six-panel flow cytometry marker for early differential diagnosis of APL from HLA-DR negative Non-APL leukemia.

Although AML-M3 (APL) and HLA-DR negative non-APL are characterized by negative HLA-DR antigen, they are different entities with similar morphology in some cases. The aim of this study is the precise, differential diagnosis of APL from HLA-DR negative non-APL by flow cytometry to narrow the diagnosis window. Bone marrow or blood samples of 580 AML patients were analyzed, and flow cytometry and molecular analysis were performed for the diagnosis of blood disorders. In 105 HLA-DR negative AML patients, expression of HLA-DR, CD33, CD117, CD11b, CD64, CD34, CD9 and myeloperoxidase staining pattern were evaluated. Fifty-six patients were diagnosed with APL, and 49 patients were diagnosed with HLA-DR negative non-APL. The APL blasts expressed CD33, CD117, CD64, and CD9 in 100%, 80.3%, 94.6%, and 100% of the cases, respectively. HLA-DR negative non-APL blasts expressed CD33, CD117, CD64 and CD9 in 75.5%, 59.1%, 32.6%, and 73.4% of the cases, respectively. APL cells were negative for HLA-DR, CD11b, and CD34 in 96.4%, 94.6%, and 91.0%, respectively. Blasts in HLA-DR negative non M3-AML were negative for CD11b, CD117, and CD34 in 77.5%, 40.9%, and 22.4%, respectively. We also investigated myeloperoxidase (MPO) staining pattern and found strong diffuse reaction in APL cells while HLA-DR negative non-APL cells showed focal positive reaction. In all of the APL patients, except for one, PML/RARA translocation was positive, and in another case with HLA-DR negative non-APL, PML/RARA and other translocations were not detected. The six-panel combination profile rapidly and specifically identifies APL from other HLA-DR negative AML.

Identification and monitoring of atypical PML/RARA fusion transcripts in acute promyelocytic leukemia.

Once the diagnostic suspicion of acute promyelocytic leukemia (APL) has been raised, international guidelines recommend prompt initiation of tailored therapy and supportive care, while awaiting for genetic confirmation of the diagnosis, and the identification of the specific PML/RARA isoform by reverse transcriptase polymerase chain reaction (RT-PCR). Depending on the PML break point, usually located within intron 6, exon 6, or intron 3, different PML/RARA transcript isoforms may be generated, that is, long (bcr1), variant (bcr2), and short (bcr3), respectively. We report here the characterization of three APL cases harboring atypical PML/RARA transcripts, which were not clearly detectable after standard RT-PCR amplification. In all three cases, clinical, morphological, and immunophenotypic features were consistent with APL. Direct sequencing allowed the identification of atypical break points within the PML and RARA genes. Then, we designed a patient-specific quantitative real-time PCR for the atypical transcripts, which allowed for specific quantitative evaluation of minimal residual disease (MRD) during follow-up. Despite the rarity of APL cases with an atypical PML/RARA fusion, our study indicates that an integrated laboratory approach, employing several diagnostic techniques is crucial to timely diagnose APL. This approach allows prompt initiation of specific targeted treatment and reliable MRD monitoring in atypical APL cases.

[Therapy-related acute promyelocytic leukemia with complex karyotype accompanied by cryptic PML/RARA on chromosome 15 by metaphase FISH].

A 53-year-old male presented with pancytopenia for 13 months. He had a past history of follicular lymphoma and hypopharyngeal cancer, which was treated via chemotherapy and radiotherapy. Bone marrow aspiration biopsy of the patient revealed a hypocellular marrow with 32% of hypergranular blasts without Auer bodies. There were also erythroid and megakaryocytic dysplasia in the bone marrow. Although the PML/RARA transcript was detected by fluorescence in situ hybridization (FISH) and reverse transcription polymerase chain reaction (RT-PCR), the G-banding karyotype analysis showed a complex karyotype without t (15;17). The PML/RARA fusion signal was identified on chromosome 15 by metaphase FISH. The patient was diagnosed of therapy-related acute promyelocytic leukemia (t-APL) with cryptic PML/RARA. He successfully attained molecular complete remission with all-trans retinoic acid (ATRA) and two courses of arsenic trioxide (ATO). He was subsequently administered nivolumab without ATRA maintenance therapy because of a progressing metastasis of a hypopharyngeal cancer to the lung. The patient had a relapse of t-APL following nine courses of nivolumab, 8 months after ending consolidation therapy with ATO. Reinduction therapy with ATRA was not effective for the relapsed t-APL that was accompanied by del (5q) and monosomy 7. Little has been previously reported on t-APL with cryptic PML/RARA. Therefore, the clinical course of this patient may provide useful insights about the characteristics of t-APL with cryptic PML/RARA.

PML/RARA inhibits expression of HSP90 and its target AKT.

Essential for cell survival, the 90 kD Heat Shock Proteins (HSP90) are molecular chaperons required for conformational stabilization and trafficking of numerous client proteins. Functional HSP90 is required for the stability of AKT, a serine-threonine kinase phosphorylated in response to growth factor stimulation. AKT plays a crucial regulatory role in differentiation, cell cycle, transcription, translation, metabolism and apoptosis. Acute promyelocytic leukaemia (APL) is characterized by the presence of the promyelocytic leukaemia/retinoic acid receptor alpha (PML/RARA) fusion protein, which deregulates expression of several genes involved in differentiation and apoptosis. Here, we report inhibition of HSP90AA1 and HSP90AB1 isomer transcription in blasts isolated from patients with APL, associated with reduction of HSP90 protein expression and loss of control on AKT protein phosphorylation. We show that in vitro treatment of PML/RARA expressing cells with all-trans retinoic acid (ATRA) up-regulates HSP90 expression and stabilizes AKT. Addition of the HSP90-inhibitor 17-(allylamino)-17-demethoxygeldanamycin in combination with ATRA, blocks upregulation of AKT protein, indicating that HSP90 is necessary for ATRA action on AKT. This is the first report proving that expression of HSP90 isomers are directly and differentially repressed by PML/RARA, with critical results on cellular homeostasis of target proteins, such as AKT, in APL blasts.

Clinician-friendly reports of molecular measurable residual disease monitoring in acute promyelocytic leukemia.

Molecular measurable residual disease (MRD) monitoring based on real-time quantitative reverse transcription PCR (RT-qPCR) plays an important role in acute promyelocytic leukemia (APL) management, but the performance status of clinical reports is unknown. This study focuses on the specific elements in molecular MRD monitoring report and their impact on clinical decision-making. The participating laboratories were asked to submit real and formal clinical reports for mock samples panel with APL clinical case. The MRD-specific elements were analyzed and summarized. The significance of longitudinal MRD monitoring curve and the missing MRD-specific elements for clinical decision-making were assessed. MRD-specific elements were significantly missing in clinical reports. The element "testing results" existed great inconsistencies in the written form of testing items and data. The longitudinal MRD monitoring curve of false-negative or false-positive MRD result was obviously different from all-correct. It not only identified MRD time point of tissue sampling relative to treatment and ensured the reliability of the negative MRD results, but also gave MRD diagnosis, clinical interpretation, and further recommendation. Clinician-friendly reports with MRD-specific elements can better serve clinical practice. The correctly intuitive results and clinically important MRD-specific elements can provide a good description of the reliability and clinical significance of MRD results.

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.

[Hypoplastic acute promyelocytic leukemia with continuous hypocellular bone marrow after remission].

An 87-year old female presented with unsteady gait and occasional subcutaneous hematomas. Blood examination findings revealed pancytopenia and mild coagulopathy. Both the histopathological evaluation of bone marrow smears and bone marrow biopsy revealed a hypocellular bone marrow. However, APL cells were observed and PML-RARA fusion gene was detected. On the basis of these findings, the patient was diagnosed with hypoplastic acute promyelocytic leukemia. She received ATRA treatment and achieved complete remission (CR) 29 days from the commencement of therapy. After the first CR, she received two courses of ATO as a consolidation therapy. Following the latter treatments, she maintained CR, but a hypoplastic bone marrow was still observed. Hypoplastic AML is defined as AML with a low bone marrow cellularity. It is clinically important to distinguish it from aplastic anemia and hypoplastic MDS. It has been suggested that both cytogenetic and morphological diagnosis are imperative to the differential diagnosis of hypocellular bone marrow.

PCGF2 negatively regulates arsenic trioxide-induced PML-RARA protein degradation via UBE2I inhibition in NB4 cells.

Arsenic trioxide (ATO) is a therapeutic agent for acute promyelocytic leukemia (APL) which induces PML-RARA protein degradation via enhanced UBE2I-mediated sumoylation. PCGF2, a Polycomb group protein, has been suggested as an anti-SUMO E3 protein by inhibiting the sumoylation of UBE2I substrates, HSF2 and RANGAP1, via direct interaction. Thus, we hypothesized that PCGF2 might play a role in ATO-induced PML-RARA degradation by interacting with UBE2I. PCGF2 protein was down-regulated upon ATO treatment in human APL cell line, NB4. Knockdown of PCGF2 in NB4 cells, in the absence of ATO treatment, was sufficient to induce sumoylation-, ubiquitylation- and PML nuclear body-mediated degradation of PML-RARA protein. Moreover, overexpression of PCGF2 protected ATO-mediated degradation of ectopic and endogenous PML-RARA in 293T and NB4 cells, respectively. In 293T cells, UBE2I-mediated PML-RARA degradation was reduced upon PCGF2 co-expression. In addition, UBE2I-mediated sumoylation of PML-RARA was reduced upon PCGF2 co-expression and PCGF2-UBE2I interaction was confirmed by co-immunoprecipitation. Likewise, endogenous PCGF2-UBE2I interaction was detected by co-immunoprecipitation and immunofluorescence assays in NB4 cells. Intriguingly, upon ATO-treatment, such interaction was disrupted and UBE2I was co-immunoprecipitated or co-localized with its SUMO substrate, PML-RARA. Taken together, our results suggested a novel role of PCGF2 in ATO-mediated degradation of PML-RARA that PCGF2 might act as a negative regulator of UBE2I via direct interaction.

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.

PML-RARa modulates the vascular signature of extracellular vesicles released by acute promyelocytic leukemia cells.

Oncogenic transformation is believed to impact the vascular phenotype and microenvironment in cancer, at least in part, through mechanisms involving extracellular vesicles (EVs). We explored these questions in the context of acute promyelocytic leukemia cells (NB4) expressing oncogenic fusion protein, PML-RARa and exquisitely sensitive to its clinically used antagonist, the all-trans retinoic acid (ATRA). We report that NB4 cells produce considerable numbers of EVs, which are readily taken up by cultured endothelial cells triggering their increased survival. NB4 EVs contain PML-RARa transcript, but no detectable protein, which is also absent in endothelial cells upon the vesicle uptake, thereby precluding an active intercellular trafficking of this oncogene in this setting. ATRA treatment changes the emission profile of NB4-related EVs resulting in preponderance of smaller vesicles, an effect that occurs in parallel with the onset of cellular differentiation. ATRA also increases IL-8 mRNA and protein content in NB4 cells and their EVs, while decreasing the levels of VEGF and tissue factor (TF). Endothelial cell uptake of NB4-derived EVs renders these cells more TF-positive and procoagulant, and this effect is diminished by pre-treatment of EV donor cells with ATRA. Profiling angiogenesis-related transcripts in intact and ATRA-treated APL cells and their EVs reveals multiple differences attributable to cellular responses and EV molecular packaging. These observations point to the potential significance of changes in the angiogenic signature and activity associated with EVs released from tumor cells subjected to targeted therapy.

Current standard treatment of adult acute promyelocytic leukaemia.

The outcome of patients with acute promyelocytic leukaemia (APL) has dramatically improved over the last two decades, due to the introduction of combined all-trans retinoic acid (ATRA) and chemotherapy regimens and, more recently, to the advent of arsenic trioxide (ATO). ATRA and anthracycline-based chemotherapy remains a widely used strategy, providing cure rates above 80%, but it is associated with risk of severe infections and occurrence of secondary leukaemias. ATO is the most effective single agent in APL and, used alone or in combination with ATRA or ATRA and reduced-intensity chemotherapy, results in greater efficacy with considerably less haematological toxicity. The toxic profile of ATO includes frequent, but manageable, QTc prolongation and increase of liver enzymes. Two large randomized studies have shown that ATRA + ATO is superior to ATRA + chemotherapy for newly diagnosed low-risk APL resulting in 2-4 year event-free survival rates above 90% and very few relapses. According to real world data, the spectacular progress in APL outcomes reported in clinical trials has not been paralleled by a significant improvement in early death rates, this remains the most challenging issue for the final cure of the disease.

Current management of newly diagnosed acute promyelocytic leukemia.

The management of acute promyelocytic leukemia (APL) has considerably evolved during the past two decades. The advent of all-trans retinoic acid (ATRA) and its inclusion in combinatorial regimens with anthracycline chemotherapy has provided cure rates exceeding 80%; however, this widely adopted approach also conveys significant toxicity including severe myelosuppression and rare occurrence of secondary leukemias. More recently, the advent of arsenic trioxide (ATO) and its use in association with ATRA with or without chemotherapy has further improved patient outcome by allowing to minimize the intensity of chemotherapy, thus reducing serious toxicity while maintaining high anti-leukemic efficacy. The advantage of ATRA-ATO over ATRA chemotherapy has been recently demonstrated in two large randomized trials and this option has now become the new standard of care in low-risk (i.e. non-hyperleukocytic) patients. In light of its rarity, abrupt onset and high risk of early death and due to specific treatment requirements, APL remains a challenging condition that needs to be managed in highly experienced centers. We review here the results of large clinical studies conducted in newly diagnosed APL as well as the recommendations for appropriate diagnosis, prevention and management of the main complications associated with modern treatment of the disease.

Chromosomal abnormality of acute promyelocytic leukemia other than PML-RARA: a case report of acute promyelocytic leukemia with del(5q).

BACKGROUND: The recent study described a better outcome in acute promyelocytic leukemia patients treated with all-trans retinoic acid and arsenic oxide compared to those treated with all-trans retinoic acid combined with conventional chemotherapy. The pivotal study indicated that favorable-risk acute promyelocytic leukemia patients can be cured without any cytotoxic chemotherapy. Even high-risk patients are treatable with cytotoxic agents. Acute promyelocytic leukemia does not develop only by the dedifferentiation caused by PML-RARA. A determined oncogene other than PML-RARA which promotes cell proliferation would be required. CASE PRESENTATION: We recently treated a 30-year-old Japanese female who achieved molecular remission with only the administration of all-trans retinoic acid. The patient's leukemic clones concomitantly had a del(5q) aberrant chromosome with t(15;17) (q22;q12). The patient's bone marrow cells indicated clonal evolution of the tumor cells expressing CD13dim, CD33+, CD117+, and lacking HLA-DR, CD34 and CD11b. A fluorescence in situ hybridization analysis detected PML-RARA fusion genes in the patient's bone marrow specimens, leading to the diagnosis of acute promyelocytic leukemia. CONCLUSION: A del(5q) is one of the characteristic chromosomal abnormalities observed in myelodysplastic syndrome. On the other hand, up to 40 % of acute promyelocytic leukemia cases are known to harbor the addition of a clonal cytogenetic abnormality. However, such a case acute promyelocytic leukemia with del(5q) would be rare, rather than myelodysplastic syndrome, consequently obtaining t(15;17). Which cytogenetic abnormalities, acute promyelocytic leukemia or myelodysplastic syndrome, came first is informative to make a clinical decision for the initial therapy. In this case, we speculated the PML-RARA translocation is an original pathogenesis and thereafter additional cytogenetic abnormalities (del(5q) and -6) common in myelodysplastic syndrome. All-trans retinoic acid lead the patient into molecular remission. We propose that an assessment of additional cytogenetic abnormality in acute promyelocytic leukemia would contribute to the clinical decisions regarding whether to treat disease with all-trans retinoic acid and cytotoxic agents. It would be of interest to know the extent of cytogenetic abnormality in the patients regarding to mixed leukemia. One or more additional cytogenetic abnormalities other than PML-RARA could account for the biological malignant grade and prognostic index.