Novel translocations in acute nonlymphocytic leukemia. Two cases involving chromosome 21, band q22

AML1 interconnected pathways of leukemogenesis

The AML1 transcription factor, identified by the cloning of the translocation t(8;21) breakpoint, is one of the most frequent targets for chromosomal translocations in leukemia. Furthermore, polysomies and point mutations can also alter AML1 function. AML1, also called CBF alpha 2, PEBP alpha 2 or RUNX1, is thus implicated in a great number of acute leukemias via a variety of pathogenic mechanisms and seems to act either as an oncogene or a tumor suppressor gene. Characterization of AML1 knockout mice has shown that AML1 is necessary for normal development of all hematopoietic lineages and alterations in the overal functional level of AML1 can have a profound effect on hematopoiesis. Numerous studies have shown that AML1 plays a vital role in the regulation of expression of many genes involved in hematopoietic cell development, and the impairment of AML1 function disregulates the pathways leading to cellular proliferation and differentiation. However, heterozygous AML1 mutations alone may not be sufficient for the development of leukemia. A cumulative process of mutagenesis involving additional genetic events in functionally related molecules, may be necessary for the development of leukemia and may determine the leukemic phenotype. We review the known AML1 target genes, AML1 interacting proteins, AML1 gene alterations and their effects on AML1 function, and mutations in AML1-related genes associated with leukemia. We discuss the interconnections between all these genes in cell signaling pathways and their importance for future therapeutic developments.

21q22 balanced chromosome aberrations in therapy-related hematopoietic disorders: report from an international workshop

The International Workshop on the relationship between prior therapy and balanced chromosome aberrations in therapy-related myelodysplastic syndromes (t-MDS) and therapy-related acute leukemia (t-AL) identified 79 of 511 (15.5%) patients with balanced 21q22 translocations. Patients were treated for their primary disease, including solid tumors (56%), hematologic malignancy (43%), and juvenile rheumatoid arthritis (single case), by radiation therapy (5 patients), chemotherapy (36 patients), or combined-modality therapy (38 patients). 21q translocations involved common partner chromosomes in 81% of cases: t(8;21) (n = 44; 56%), t(3;21) (n = 16; 20%), and t(16;21) (n = 4; 5%). Translocations involving 15 other partner chromosomes were also documented with involvement of AML1(CBFA2/RUNX1), identifying a total of 23 different 21q22/AML1 translocations. The data analysis was carried out on the basis of five subsets of 21q22 cases, that is, t(8;21) with and without additional aberrations, t(3;21), t(16;21), and other 21q22 translocations. Dysplastic features were present in all 21q22 cases. Therapy-related acute myeloid leukemia (t-AML) at presentation was highest in t(8;21) (82%) and lowest in t(3;21) (37.5%) patients. Cumulative drug dose exposure scores for alkylating agents (AAs) and topoisomerase II inhibitors indicated that t(3;21) patients received the most intensive therapy among the five 21q22 subsets, and the median AA score for patients with secondary chromosome 7 aberrations was double the AA score for the entire 21q22 group. All five patients who received only radiation therapy had t(8;21) t-AML. The median latency and overall survival (OS) for 21q22 patients were 39 and 14 months (mo), compared to 26 and 8 mo for 11q23 patients, 22 and 28 mo for inv(16), 69 and 7 mo for Rare recurring aberrations, and 59 and 7 mo for Unique (nonrecurring) balanced aberration (latency P < or = 0.016 for all pairwise comparisons; OS, P < or = 0.018 for all pairwise comparisons). The percentages of 21q22 patients surviving 1 year, 2 years, and 5 years were 58%, 33%, and 18%, respectively. Noticeable differences were observed in median OS between 21q22 patients (n = 7) receiving transplant (BMT) (31 mo) compared to 21q22 patients who received intensive non-BMT therapy (n = 46) (17 mo); however, this was nonsignificant because of the small sample size (log-rank, P = 0.33). t-MDS/t-AML with balanced 21q22 aberrations was associated with prior exposure to radiation, epipodophyllotoxins, and anthracyclines, dysplastic morphologic features, multiple partner chromosomes, and longer latency periods when compared to 11q23 and inv(16) t-MDS/AML Workshop subgroups. In general, patients could be divided into two prognostic risk groups, those with t(8;21) (median OS, 19 mo) and those without t(8;21) (median OS, 7 mo) leukemia (log-rank, P = 0.0007).

Identification of chromosomal rearrangements in the human myeloid leukemia cell line GF-D8 by dual-colour fluorescence in situ hybridization

Fluorescence In Situ Hybridization (FISH) studies with chromosome-specific libraries and repetitive probes were performed on the human acute myeloid leukemia cell line GF-D8 in order to define the complex chromosomal rearrangements observed by conventional cytogenetic analysis. Two-colour FISH with whole chromosome painting probes 8 and 11 showed that the add(8) chromosome had an 11-derived region inserted at q24, whereas the add(11) chromosome had an 8-derived region translocated onto q23. It also demonstrated that no normal chromosome 11 is present in GF-D8 cells, since a translocation involving chromosomes 11 and 17q was detected in addition to the add(11). The der(7) chromosome with extra material in its long arm, identified by QFQ and GTG banding, turned out to have a chromosome 15-derived segment translocated to q22. The deletion of 7q was proved to be interstitial, as the 7q-specific telomere as well as a tiny 7-specific band were observed on an unknown chromosome. Fine mapping of the breakpoints involved in the multiple chromosomal rearrangements of the GF-D8 cell line might provide insights into the mechanisms of myeloid leukaemogenesis.

Translocation (3;21)(q26;q22) in therapy-related myelodysplasia following drugs targeting DNA-topoisomerase II combined with alkylating agents, and in myeloproliferative disorders undergoing spontaneous leukemic transformation

Translocation (3;21)(q26;q22) has been observed only rarely in de novo myelodysplasia (MDS) and de novo acute myeloid leukemia (AML), but, including the two new cases in the present study, the aberration has now been identified in at least 10 cases of t-MDS or t-AML. All these 10 patients had previously received alkylating agents, in nine patients combined with a drug targeting at DNA-topoisomerase II (doxorubicin in eight cases). Eight of the ten patients presented with t-MDS. A further 20 patients with various myeloproliferative disorders and an identical t(3;21) have been reported. In these cases, t(3;21) was not related to any specific type of previous therapy but was associated with transformation from chronic stage disease to overt AML.

X and Y chromosome loss as sole abnormality in acute non-lymphocytic leukemia (ANLL)

Of the 9300 bone marrows and peripheral bloods analyzed for hematologic disease in our laboratory between 1978 and 1990, 240 patients exhibited X or Y loss of chromosomes. Of those 240 patients only two could be positively associated with acute leukemia and no other observable chromosome involvement. The evidence presented here, albeit represented by only two patients, proves that sex chromosome loss as the sole abnormality can be a clonal cytogenetic marker for acute leukemia. One patient was a 48-year-old man with loss of the Y in 93% of his bone marrow metaphases and the other patient was a 53-year-old woman with 100% loss of the X in her bone marrow metaphases (perhaps the first such report of a woman). After therapy, both remission bone marrow analyses showed complete reappearance of the respective sex chromosomes.

AML with unusual chromosomal changes. Translocation (15;21) and 5q- in the presence of two normal chromosomes 5

We performed serial cytogenetic studies of the bone marrow (BM) of a patient with acute myeloblastic leukemia (AML) and noted abnormal karyotypes 47,XY,+del(5)(q12q34),t(15;21)(q21;q22)/47,XY,+del(5)(q12q34 ) during the second relapse. Although a case of this t(15;21) was recently observed in a female patient with acute nonlymphocytic leukemia (ANLL) of subtype M4 of the French-American-British (FAB) classification, the present article constitutes the first report of its occurrence in association with ANLL of subtype M1-M2. Furthermore, the presence of the 5q- accompanied by two chromosomes 5 of normal appearance is very rare and of great interest.

Cytogenetic analysis in children with acute nonlymphocytic leukemia

In this work we present the results of cytogenetic analysis of the malignant cells in 27 children with acute nonlymphocytic leukemia (ANLL). The aim of our investigations was to determine the frequency and types of chromosome aberrations in our population of children with ANLL. Successful cytogenetic analysis was carried out in 24 (89%) patients. Aberrant karyotypes of malignant cells were established in 58% of the cases. The most frequent chromosomal abnormality was t(8;21), identified in 5 (20.8%) patients, i.e., 4 of 10 M2-ANLL. Aberration frequency of chromosome 11 was 16.6% and was identified in 3 of 8 M5-ANLL. Trisomy 8 and monosomy 7 were identified in one patient each with M3 and M2-ANLL, respectively. del(13), a rare chromosome aberration in hemoblastoses, was found in a child with M1,t(8;21) and the loss of chromosome Y. Translocation t(1;11;21) with a break in regions 1q23, 11q23, and 21q22, is unusual and was identified in a boy with M2-ANLL; it can be considered as a variant form of the t(8;21).

Translocation (3;21) characterizes crises in myeloid stem cell disorders

Three patients, one with Philadelphia (Ph) chromosome positive chronic myelocytic leukemia (CML) and two with primary acquired myelodysplastic syndromes (MDS), have been identified to have a t(3;21)(q26;q22). In the patient with CML, the t(3;21) was detected only in the blast phase. The t(3;21) as the sole abnormality appeared at presentation of MDS [refractory anemia with excess blasts (RAEB)] in one patient and remained as such when progression to RAEB in transformation (RAEB-t) occurred. The other patient with MDS had the t(3;21), in addition to other changes, during the progression of the disease. Thus, t(3;21) may characterize myeloid crises of clonal hematopoietic stem cell disorders (HSCD) and indicates a poor prognosis. As a primary cytogenetic event it may be also involved in the genesis of myelodysplasia with subsequent leukemic transformation.

Multiple clones with (3;21) translocation in a case of Ph-positive chronic myelogenous leukemia during relapse after allogeneic bone marrow transplantation

Secondary chromosome changes are frequently observed during the blastic phase of chronic myelogenous leukemia (CML) owing to clonal evolution. Both numerical and structural abnormalities are reported in most of these cases. Recently a new translocation, t(3;21)(q26;q22), was reported in Philadelphia (Ph)-positive CML during the chronic as well as accelerated phase. We report a patient with Ph-positive CML who developed three abnormal clones, all of which had t(3;21) at the time of relapse after allogeneic bone marrow transplantation during the accelerated phase.