The significance of cytogenetic findings of erythroid colonies derived from a Ph+ ALL patient: fundamental differences between Ph+ ALL and blastic phase CML

Bcr-Abl variants: biological and clinical aspects

Bcr-Abl is an oncogene that arises from fusion of the Bcr gene with the c-Abl proto-oncogene. Three different Bcr-Abl variants can be formed, depending on the amount of Bcr gene included: p185, p210, and p230. The three variants are associated with distinct types of human leukemias. Examination of the signaling pathways differentially regulated by the Bcr-Abl proteins will help us gain better insight into Bcr-Abl mediated leukemogenesis.

The existence of lymphoid lineage restricted Philadelphia chromosome-positive acute lymphoblastic leukemia with heterogeneous bcr-abl rearrangement

Analysis of lineage involvement was performed in 17 Philadelphia chromosome-positive acute lymphoblastic leukemia patients with no history of chronic myeloproliferative disorder. The percentage of blastic cells as defined by flow cytometry matched that of the Ph-positive cells in 14 out of 17 patients. The bcr-abl rearrangement was investigated by fluorescent in situ hybridization in morphologically identified blastic cells, myeloid elements, lymphocytes and erythroblasts using a combined light and fluorescent microscopical imaging. Lymphoid lineage restriction could be determined in all but three of the patients. These 14 patients exhibited heterogeneity in terms of m-bcr and M-bcr types of translocation as revealed by reverse transcription polymerase chain reaction. The three patients with multilineage involvement and M-bcr type of translocation reverted to chronic phase and the percentage of Ph-positive cells remained high. Thus, we could identify an uncommitted stem cell origin among Ph-positive ALLs only in those patients whose disease subsequently proved to be a lymphoid blastic crisis with clinically silent chronic phase.

Differences between blastic chronic myeloid leukemia and Ph-positive acute leukemia

Cytogenetic and molecular characteristics of chronic myeloid leukemia in blast crisis and Ph-positive acute leukemia are compared. The main differences relate to the presence of Ph-negative metaphases at diagnosis and the disappearance of Ph in complete remission in acute leukemia, and the localization of the chromosome breakpoints in the BCR gene, in the bcr segment in chronic leukemia and in the first intron of the BCR gene in 50% of acute leukemias. The profiles of these abnormalities, as well as the types of additional chromosome changes, are not sufficient to distinguish between the two disorders in every patient. The distinction between these two entities, which is possible in the majority of patients, will be improved by results of experimental work currently in progress in many laboratories.

Philadelphia chromosome-positive leukaemia: the translocated genes and their gene products

Overwhelming evidence indicates a role for the deregulated ABL protein tyrosine kinase in the aetiology of CML and Ph-positive acute leukaemia. These disorders are characterized by the generation of BCR/ABL fusion proteins with elevated tyrosine kinase activity. Although much is known concerning the transforming potential of ABL proteins in various systems, very little is understood of the normal function and mode of regulation of ABL activity. The mechanism of oncogenic activation is therefore also obscure. In spite of this, our understanding of the molecular details of these chromosomal translocations allows the design of therapies directed against their unique, leukaemia-specific proteins and RNA products.

Philadelphia chromosome negative acute lymphoblastic leukemia preceding Philadelphia positive chronic myelogenous leukemia

A patient with Philadelphia chromosome (Ph) negative acute lymphoblastic leukemia (ALL, FAB type L1) developed Ph-positive chronic myelogenous leukemia (CML) after more than 2 years in complete remission. Subsequently, Ph-positive lymphoblastic transformation occurred, which was again successfully treated. Thereafter, the CML state was interrupted twice more by blast crisis. The additional chromosomal abnormalities were atypical for Ph-positive CML. The course is interpreted as a possible example of the multistep development of CML. Blastic transformation occurring prior to the Ph chromosome has been reported in only two cases previously.

Molecular analysis of chromosome 22 breakpoints in adult Philadelphia-positive acute lymphoblastic leukaemia

The Philadelphia (Ph) translocation, t(9:22)(q 34:q11), is found in the majority of patients with chronic myelogenous leukaemia (CML) as well as in approximately 20% of adult acute lymphoblastic leukaemia (ALL) patients. The chromosome 22 breakpoint in CML has been localized within a restricted 5.8 kb segment of DNA known as the breakpoint cluster region (bcr). To investigate the chromosome 22 breakpoint in ALL, we analysed five adult Ph-positive ALL patients for bcr rearrangement. Rearrangement was detected within bcr in two patients. However, in one patient the break occurred 5' to the first exon of bcr and in two patients the bcr region was not involved. We conclude that the identical cytogenetic marker, t(9:22), may yield a different genomic configuration in ALL and CML.

Chromosome studies of hematopoietic colonies for distinct diagnosis of megakaryoblastic crisis of chronic myelogenous leukemia: a case report

Chromosome studies of cells from megakaryocytic colonies (CFU-Meg) as evidenced by a megakaryocyte-specific monoclonal antibody, TP80, from a patient with chronic myelogenous leukemia (CML) in the blast crisis (BC) revealed the same aberrant karyotype, 52,XY,+9,+9,+18,+19,+21,+22,t(9;22)(q34;q11),t(9;22), as that having newly appeared in the peripheral blood. Cells from erythroid bursts (BFU-E) showed only the standard 46,XY,t(9;22) karyotype, and cells from granulocyte/macrophage colonies (CFU-GM) had either of these karyotypes. These results demonstrated that the whole megakaryocytic line and part of the granulocyte/macrophage line had been involved in the BC while the erythroid line totally belonged to the original clone. Chromosome analysis coupled with immunophenotyping of hemopoietic colonies was useful for a definite diagnosis of megakaryoblastic crisis of CML in this patient.