APL-like Leukemias Research Articles

APL-like leukemia with chromosomal translocation t(16;17): a case report and literature review

Variant acute promyelocytic leukemia (APL) and APL-like leukemia are rare types of APL, with t (16;17) chromosome abnormality being even rarer. An APL-like patient with t (16;17) chromosome abnormality, which was characterized by bone, lymph node, and central nervous system involvement, was admitted to our hospital. He achieved complete remission after several cycles of chemotherapy and subsequently underwent hematopoietic stem cell transplantation. Furthermore, the diagnosis and treatment of this patient were reported and a literature review was conducted.

19. High resolution cytogenomic analysis reveals characterizing abnormalities in APL-like leukemia

19. High resolution cytogenomic analysis reveals characterizing abnormalities in APL-like leukemia

Obesity-Driven Acceleration of Acute Promyelocytic Leukemia Development in Mice with Inserted PML-RARa

While a number of solid tumors are identified as obesity-associated cancers, multiple myeloma and acute promyelocytic leukemia (APL) are the only hematologic malignancies included in this category. APL is a highly treatable form of AML characterized by maturation arrest at the promyelocyte stage, and frequent cures with combined ATRA and Arsenic Trioxide therapy. APL is initiated by a chromosomal translocation that causes the fusion of thePMLandRARAgenes, leading to the production of PML-RARA protein. To determine if obesity accelerates the development of APL, we used a genetically-engineered knock-in model in which human PML-RARA cDNA was inserted into the 5' untranslated region of the murine cathepsin G gene (Ctsg), which targets expression to early myeloid progenitor cells. This knock-in transgene was extensively backcrossed (>20 generations) into the C57BL/6J (B6) genetic background, which has been consistently shown to render mice susceptible to diet-induced obesity.Ctsg-PML-RARA mice developed on the B6 background generate a lethal APL-like leukemia with a latency of 8-12 months, and a penetrance of about 60%, as cooperating mutations occur and cause clinical disease. We placed cohorts of B6.Ctsg-PML-RARA heterozygous (mCG+/PR) and wild-type (WT) mice, genotyped by PCR, on high-fat (HFD) [57% coconut oil fat] and low-fat (LFD) [10% coconut oil fat] diets, collecting peripheral blood via the retro- orbital sinus at 30 day intervals and performing automated blood counts to observe temporal associations in disease development. HFD feeding significantly accelerated the development of APL in mCG+/PR mice, leading to anemia, thrombocytopenia, leukocytosis of the granulocyte series, and splenomegaly. Survival rate reduction demonstrated sexual-dimorphism, with male HFD-fed mCG+/PR mice displaying a median leukemia-free survival time of 211 days compared to 266 days in the female HFD-fed mCG+/PR cohort. In contrast, LFD-fed mCG+/PR male mice showed a median survival time of 318 days, whereas none of LFD-fed mCG+/PR female group nor any of the WT groups on HFD or LFD have reached median survival as of 325 days. Moreover, no signs of leukemia were observed in either HFD- and LFD-fed WT groups, indicating that adiposity alone had no leukemogenic effect. These studies clearly demonstrate that obesity accelerates leukemogenesis in theCtsg-PML-RARA mouse model of acute promyelocytic leukemia. High density flow cytometry will be applied in the bone marrow of the different groups to evaluate the modulation of multiple hematopoietic cell lineages and cell surface markers. Disclosures No relevant conflicts of interest to declare.

Acute Myeloid Leukemia With Recurrent Cytogenetic Abnormalities.

Session 1 of the 2013 Society for Hematopathology/European Association for Hematopathology Workshop was devoted to the cases of acute myeloid leukemia (AML) with recurrent cytogenetic abnormalities. Based on World Health Organization 2008 criteria, seven specific translocations are defined as "recurrent" in AML. Of these seven, three are considered to be AML defining regardless of blast percentage. Workshop cases provided the opportunity to consider potential new AML-defining cytogenetic mutations, as well as other unique aspects of AML with cytogenetic abnormalities. Most of the 38 cases submitted were acute promyelocytic leukemia (APL) with t(15;17)(q24.1;q21.1) and so-called variants (12 cases), AML with t(8;21)(q22;q22) (seven cases), AML with inv(3)(q11q26.2) (six cases), and AML with 11q23 translocations (five cases). This review focuses on providing updated recommendations for the rapid diagnosis of APL, discussing the types and significance of variant RARA mutations in APL-like leukemias, and refining low-blast-count (oligoblastic) AML. In addition, the significance of unique morphologic, immunophenotypic, and genetic variations in AML defined by a recurrent cytogenetic abnormality is included.

Concomitant and successive amplifications of MYC in APL-like leukemia

A 61-year-old male patient presented with very high blood white cell count, left shift of granulocytes to blasts, as well as low hemoglobin and platelets. The bone marrow aspirate and biopsy were consistent with an acute myeloid leukemia (AML). Blasts presented with large azurophilic inclusions and prominent Auer rods resembling acute promyelocytic leukemia (APL). Cytogenetic analysis revealed a deletion 9p and double-minute chromosomes. Fluorescence in situ hybridization showed amplification of the MYC probe and the absence of a RARA rearrangement. The patient achieved complete morphologic and cytogenetic remission 1 month after allogenic transplant, but relapsed 1 month later. Cytogenetics showed MYC amplification as a homogeneously staining region inserted into the long arm of one chromosome 9 and as a ring structure. At least five other acute promyelocytic leukemia-like cases without translocation 15;17, but with double minutes, have been reported in the literature. Only one of these had no RARA rearrangement. This report presents a second patient with APL-like bone marrow morphology, absence of RARA rearrangement, and MYC amplification. In this case, the amplification happened in various concomitant or successive forms.

Myc Drives Chromosomal Gain in Acute Myeloid Leukemia

Acute Myeloid Leukemia (AML) is a disease characterized by diverse genetic pathogenesis, including both balanced and unbalanced chromosomal aberrations. Much is known regarding the pathogenic effects of balanced rearrangements in AML, whereas our understanding of how unbalanced aberrations contribute to leukemia is more limited. The balanced t(15;17) chromosomal rearrangement is a nearly constant feature of acute promyeloctyic leukemia (APL), a subtype AML. The translocation fuses the promyelocytic leukemia gene (PML) to the retinoic acid receptor α gene (RARA). Trisomy 8 is the most common secondary karyotypic lesion observed in APL, and it has been speculated but not proven that the MYC gene contributes to this chromosomal gain. We previously reported that mouse chromosome 15, which contains the mouse Myc gene in a region syntenic to human chromosome 8q24, is commonly gained in the MRP8 PML-RARA mouse model of APL. We now report our work to assess the hypothesis that increased MYC cooperates with PML-RARα to accelerate disease and that gain of MYC/Myc drives +8 in humans and +15 in mice. Expressing MYC with a retroviral vector in PML-RARA bone marrow led to the rapid development of APL-like leukemias (3 months vs. 8.5 months with PML-RARA alone). Chromosome 15 was not gained in any of the leukemias, although 70% had other clonal karyotypic abnormalities. This finding suggests that when MYC is overexpressed, there is no selective pressure to gain chromosome 15, supporting our hypothesis that Myc is driving this gain. We also generated PML-RARA mice haploinsufficient for Myc to examine the effect of decreasing MYC levels. The median latency among leukemic animals was 258 days for mice with PML-RARA and two wild-type Myc alleles, whereas the latency was increased to 339 days for PML-RARA Myc haploinsufficient mice. Hence, lower MYC expression served as a check on leukemic transformation. Furthermore, the majority of the leukemias that arose in Myc haploinsufficient mice had gained wild-type Myc. These data demonstrate a selective pressure for Myc gain. Additional experiments showed thatas MYC expression increases there is a decrease in both latency and genetic complexity of leukemias that arise, thatMYC and PML-RARα interact to disrupt myeloid differentiation in vivo and thatalthough MYC cooperates with PML-RARα to cause leukemia, additional events are required for completing transformation even at high levels of MYC.Altogether our studies of increased and decreased MYC expression in PML-RARA mice show a strong correlation between MYC dosage and leukemic transformation. Our results suggest that agents that target MYC might be useful for the treatment of AML.

Forced retinoic acid receptor α homodimers prime mice for APL-like leukemia

RARA becomes an acute promyelocytic leukemia (APL) oncogene by fusion with any of five translocation partners. Unlike RARalpha, the fusion proteins homodimerize, which may be central to oncogenic activation. This model was tested by replacing PML with dimerization domains from p50NFkappaB (p50-RARalpha) or the rapamycin-sensitive dimerizing peptide of FKBP12 (F3-RARalpha). The X-RARalpha fusions recapitulated in vitro activities of PML-RARalpha. For F3-RARalpha, these properties were rapamycin sensitive. Although in vivo the artificial fusions alone are poor initiators of leukemia, p50-RARalpha readily cooperates with an activated mutant CDw131 to induce APL-like disease. These results demonstrate that the dimerization interface of RARalpha fusion partners is a critical element in APL pathogenesis while pointing to other features of PML for enhancing penetrance and progression.

Cooperative Pathways to Acute Myeloid Leukemia Include the Combining of Transcription Factor Alterations: PML-RARα Cooperates with SOX4.

One paradigm for transformation of normal myeloid cells into acute myeloid leukemia (AML) is the combining of transcription factor alteration with activation of signaling pathways, including cytokine receptor activation. To identify possible alternative pathways to leukemogenesis we crossed MRP8-PML/RARA transgenic mice with BXH-2 mice, which harbor an endogenous retrovirus that causes AML. Approximately half of the leukemias that arose in this cross showed features of acute promyelocytic leukemia (APL). We identified 22 insertions sites in 8 APL-like leukemias. Of these, 7 represented common insertion sites in the Mouse Retroviral Tagged Cancer Gene Database (RTCGD, http://rtcgd.ncifcrf.gov/mm4/index.html). We introduced into a retroviral vector cDNAs encoding 6 genes located at retroviral insertion sites identified in PML/RARA leukemias (Sox4, Meis1, Lck, Sfpi1, Nfil3, Cblb). PML/RARA transgenic bone marrow was transduced with these retroviruses and the marrow was used to reconstitute lethally irradiated recipient animals. Recipients of PML/RARα transgenic marrow transduced with a SOX4 retrovirus developed APL-like leukemias in 3 months. SOX4 is an HMG box transcription factor that exhibits sequence specific DNA binding and transactivation. It is the most common insertion site in RTCGD, and has been found to be overexpressed in small cell lung cancer and medulloblastoma, as well as other tumors. In light of other data indicating that combining transcription factor abnormalities can rapidly induce leukemia (e.g. Hoxa9 + Meis1), our finding that SOX4 + PML/RARα is potently leukemogenic supports the hypothesis that such cooperativity represents another important paradigm in myeloid leukemogenesis.

Leukemias resembling acute promyelocytic leukemia, microgranular variant.

Acute promyelocytic leukemia (APL) should be distinguished from other subtypes of acute myeloid leukemia (AML) because of the increased risk of disseminated intravascular coagulation (DIC) and its response to arsenic compounds and retinoids. Some cases of AML seem morphologically similar to the microgranular variant of APL (French-American-British [FAB] AML-M3v) but lack the t(15;17). We evaluated 8 cases of APL-like leukemias for subtle morphologic, cytochemical, immunophenotypic, and cytogenetic differences compared with 5 cases of promyelocytic leukemia/retinoic receptor alpha (PML/RARalpha)-positive APL (FAB AML-M3v). We also evaluated both groups for the presence of DIC. No differences among the groups were noted in blast size, chromatin pattern, nuclear morphologic features, intensity of myeloperoxidase staining, or presence of Auer rods. Immunophenotypes were similar; both types of cases lacked CD34 and HLA-DR and were CD13+ and CD33+. Two cases of APL-like leukemias also were CD56+. DIC was present in 2 patients with M3v. Our study shows that there are no definitive morphologic, cytochemical, or immunophenotypic findings that can distinguish these cases from PML/RARalpha-positive APL.

Variant and masked translocations in acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is characterized by a unique hemorrhagic syndrome, disseminated intravascular coagulation, and the association with the specific (15;17 chi q22-23:q12-21) translocation, which disrupts the retinoic acid receptor alpha (RARA) and the promyelocytic leukemia (PML) genes. The t(15;17) leads to the formation of two reciprocal fusion genes, PML/RARA on chromosome 15 and RARA/PML on chromosome 17; it is responsible for the unique response of the disease to retinoic acid (ATRA) treatment. As was described for chronic myeloid leukemia and its associated t(9;22) [Philadelphia chromosome], variant translocations have been reported in APL, which are either complex translocations involving additional chromosome(s), or simple variant translocations involving only either one chromosome 15 or 17 and any of several chromosomes. Rearrangements of RARA and PML were documented in some of these variant translocations. In contrast, recent molecular analysis of APL cases with cytogenetically normal chromosomes 15 and 17 revealed the occurrence of submicroscopic translocations, leading to the formation of non reciprocal fusion genes, either PML/RARA or RARA/PML only. Detailed analysis of such cases may shed light on the mechanisms of translocation, on the selection of oncogenic products, and on the respective role(s) of the products of the translocation. Demonstration of the existence, in some APL-like leukemias, of masked translocations with involvement of PML and RARA, thus allows to (i) confirm the diagnosis of APL, (ii) adapt the treatment and (iii) monitor the residual disease. Finally APL-like leukemias were recently reported, with either a t(11;17) or t(5;17), resulting in the fusion of RARA to genes other than PML; these patients do not appear to respond to ATRA treatment. Altogether, these results emphasize the usefulness of a molecular definition of APL.