Fluorescent In Situ Hybridization Analysis of Philadelphia Chromosome-Negative Chronic Myeloid Leukemia with the bcr/abl Fusion Gene

Chronic myeloid leukemia with insertion-derived BCR-ABL1 fusion: redefining complex chromosomal abnormalities by correlation of FISH and karyotype predicts prognosis

Chromosomal insertion-derived BCR-ABL1 fusion is rare and mostly cryptic in chronic myeloid leukemia (CML). Most of these cases present a normal karyotype, and their risk and/or prognostic category are uncertain. We searched our database and identified 41 CML patients (20 M/21 F, median age: 47 years, range 12-78 years) with insertion-derived BCR-ABL1 confirmed by various FISH techniques: 31 in chronic phase, 1 in accelerated phase, and 9 in blast phase at time of diagnosis. Conventional cytogenetics analysis showed a normal karyotype (n = 19); abnormal karyotype with morphologically normal chromosomes 9 and 22 (n = 5); apparent ins(9;22) (n = 2) and abnormal karyotype with apparent abnormal chromosomes 9, der(9) and/or 22, der(22) (n = 15). The locations of insertion-derived BCR-ABL1 were identified on chromosome 22 (68.3%), 9 (29.3%), and 19 (2.4%). Complex chromosomal abnormalities were often overlooked by conventional cytogenetics but identified by FISH tests in many cases. After a median follow-up of 58 months (range 1-242 months), 11 patients died, and 3 lost contact, while the others achieved different cytogenetic/molecular responses. The locations of BCR-ABL1 (der(22) vs. non-der(22)) and the karyotype results (complex karyotype vs. noncomplex karyotype) by conventional cytogenetics were not associated with overall survival in this cohort. However, redefining the complexity of chromosomal abnormality by correlating karyotype and FISH findings, CML cases with simple chromosomal abnormalities had a more favorable overall survival than that with complex chromosomal abnormalities. We conclude that insertion-derived BCR-ABL1 fusions often involve complex chromosomal abnormalities which are overlooked by conventional cytogenetics, but can be identified by one or more FISH tests. We also suggest that the traditional cytogenetic response criteria may not apply in these patients, and the complexity of chromosomal abnormalities redefined by correlating karyotype and FISH findings can plays a role in stratifying patients into more suitable risk groups for predicting prognosis. (Word count: 292).

Detection of the CBFB/MYH11 fusion gene in de novo acute myeloid leukemia (AML): A single-institution study of 224 Japanese AML patients

The cytogenetic findings in acute myeloid leukemia (AML) are a powerful prognostic indicator. Among these abnormalities, the World Health Organization has classified inv(16)(p13q22), which is closely associated with the M4E classification in the French-American-British system, as indicating a good-risk AML. However, this chromosomal abnormality can often be difficult to detect. In this study, we used RT-PCR and FISH analysis to examine 224 Japanese adult de novo AML patients for the presence of the CBFB/MYH11 fusion transcript at the time of diagnosis. The CBFB/MYH11 fusion gene was detected in 17 patients (7.6%): eight patients had the inv(16) chromosome and in all of them it was M4E; nine patients did not have abnormalities in chromosome 16. AML with the CBFB/MYH11 fusion gene but without inv(16) was found in M2, M4, and M5, but not in M4E patients. There were no statistically significant differences in the clinical features of patients with the inv(16) and those with the cryptic inv(16) chromosome. These results indicate that even if eosinophilia is not found, molecular screening for CBFB/MYH11 fusion gene should be performed in all AML patients at the time of diagnosis to help guide disease management.

Generation of the BCR/ABL fusion gene in a Philadelphia chromosome-negative chronic myeloid leukaemia: insertion of 5.6 Mb of 9q34 into the BCR region of chromosome 22

This report describes a chronic myelogenous leukaemia patient with an apparently normal bone marrow karyotype but BCR/ABL fusion-gene-positive. Commercial FISH probes showed an atypical pattern and the BCR/ABL fusion transcript was detected by RT-PCR, but not the reciprocal ABL/BCR. Consecutive FISH assays clarified the mechanism of the masked Ph. The ABL gene and the following 5.6-5.7 Mb of 9q are inserted into the BCR region of chromosome 22. There is no transference of 22q material to chromosome 9 or to any other chromosomes. Clinical features and evolution of the patient are similar to those cases with classic Ph chromosome.

Granulocytic sarcoma of mesentery in acute myeloid leukemia with CBFB/MYH11 fusion gene but not inv(16) chromosome: Case report and review of literature

Granulocytic sarcoma (GS) is a rare extra-medullary tumor and usually involves the skin, soft tissue, and lymph nodes. GS is found in 8% of acute myeloid leukemia (AML) patients, especially patients with t(8;21)AML. It has been suggested that GS is a poor prognostic factor in t(8;21)AML. Compared to t(8;21)AML, GS is rare in cases of inv(16)AML. Thus, the characteristics of inv(16) with GS are not well understood. Here, we describe a patient with AML and mesentery GS. The chromosomal analysis was normal, but molecular analysis detected the CBFB/MYH11 fusion gene in the blasts. A complete remission was achieved with standard induction therapy followed by high-dose cytarabine consolidation. We have also summarized 12 reported cases of inv(16)AML with GS and found that GS was commonly found in abdominal lesions. These observations suggest that when abdominal GS is diagnosed, an analysis of the CBFB/MYH11 fusion gene is necessary to make an appropriate decision regarding treatment options, even if no chromosomal abnormalities are found.

Molecular and phenotypic analysis of Philadelphia chromosome-positive bilineage leukemia: possibility of a lineage switch from T-lymphoid leukemic progenitor to myeloid cells

The occurrence of acute bilineage leukemia is thought to be the malignant transformation of a myeloid or lymphoid leukemic progenitor with the potential to differentiate into the other lineages; however, the mechanisms of this lineage switch are not well understood. Here, we report on the extremely rare case of adult Philadelphia chromosome-positive acute bilineage leukemia, which is characterized by T-cell acute lymphoblastic leukemia and acute myelomonocytic leukemia. Chromosome analysis showed 46,XY,del(7)(p11.2),t(9;22)(q34;q11.2) in all metaphases and a minor BCR/ABL chimeric gene was detected in these leukemic cells by PT-PCR. When the CD5+ and CD5- cells were sorted, a fusion gene of BCR/ABL and the same clonally rearranged band of a T-cell receptor (TCR) gene were detected in both populations. Nucleotide sequencing of the TCR-gamma gene revealed the clonal rearrangement of the V8-JGT2 complex in both populations. Overexpression of PU.1, which plays a fundamental role in myelomonocyte development, was found in the sorted CD34+CD7+ and CD5-, but not CD5+ cells. These results suggest that leukemic progenitor cells in the T-lineage with the del(7) and t(9;22) have the potential to differentiate into myeloid lineage, and that enforced PU.1 expression may contribute in part of this phenomenon.