Problems with interphase fluorescence in situ hybridization in detecting BCR/ABL-positive cells in some patients using a novel technique with extra signals

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).

Aberrations of chromosomes 9 and 22 in acute lymphoblastic leukemia cases detected by ES-fluorescence in situ hybridization

A reciprocal translocation between chromosomes 9 and 22 creates oncogenic BCR/ABL fusion in the breakpoint region of the derivative chromosome 22. The aim of this study was to evaluate the importance of atypical fluorescence in situ hybridization (FISH) signal patterns in pediatric and adult acute lymphoblastic leukemia (ALL) cases. We evaluated t(9;22) translocation in 208 cases with ALL (294 tests), including 139 childhood and 69 adult cases by FISH technique using BCR/ABL extra signal (ES) probe. FISH signal patterns observed in pediatric ALL cases were as follows; Major-BCR/ABL (M-BCR/ABL) (1.4%), minor-BCR/ABL (m-BCR/ABL) (3.6%), trisomy 9 (4.3%), trisomy 22 (4.3%), trisomy or tetrasomy of both chromosomes 9 and 22 (2.9%), monosomy 9 (1.4%), monosomy 22 (0.7%), ABL gene amplification (1.4%), derivative chromosome 9 deletion (1.4%), and extra copies of the Philadelphia chromosome (1.4%). FISH signal patterns observed in adult ALL cases were as follows; M-BCR/ABL (5.8%), m-BCR/ABL (11.6%), two different cell clones with major and minor BCR/ABL signal pattern (2.9%), extra copies of Philadelphia chromosome (4.3%), derivative chromosome 9 deletion (1.4%), trisomy 9 (2.9%), tetraploidy (1.4%), monosomy 9 (1.4%), trisomy 22 (1.4%), and coexistence of both trisomy 22 and monosomy 9 (1.4%). Trisomy 9, trisomy 22, and polyploidy of chromosomes 9 and 22 were specific atypical FISH signal patterns for childhood B cell acute lymphoblastic leukemia (B-ALL) patients. However, monosomy 9 and ABL gene amplification were highly specific for childhood T cell acute lymphoblastic leukemia (T-ALL) patients. Our report presents the correlation between atypical FISH signal patterns and clinical findings of a large group of ALL cases.

Automated fluorescent in situ hybridization (FISH) analysis of t(9;22)(q34;q11) in interphase nuclei

BACKGROUND

For chronic myeloid leukemia, the FISH detection of t(9;22)(q34;q11) in interphase nuclei of peripheral leukocytes is an alternative method to bone marrow karyotyping for monitoring treatment. With automation, several drawbacks of manual analysis may be circumvented. In this article, the capabilities of a commercially available automated image acquisition and analysis system were determined by detecting t(9;22)(q34;q11) in interphase nuclei of peripheral leukocytes.

METHODS

Three peripheral blood samples of normal adults, 21 samples of CML patients, and one sample of a t(9;22)(q34;q11) positive cell-line were used.

RESULTS

Single nuclei with correctly detected signals amounted to 99.6% of nuclei analyzed after exclusion of overlapping nuclei and nuclei with incorrect signal detection. A cut-off value of 0.84 mum was defined to discriminate between translocation positive and negative nuclei based on the shortest distance between signals. Using this value, the false positive rate of the automated analysis for negative samples was 7.0%, whereas that of the manual analysis was 5.8%. Automated and manual results showed strong correlation (R(2) = 0.985), the mean difference of results was only 3.7%.

CONCLUSIONS

A reliable and objective automated analysis of large numbers of cells is possible, avoiding interobserver variability and producing statistically more accurate results than manual evaluation.

Early blastic transformation following complete cytogenetic response in a pediatric chronic myeloid leukemia patient treated with imatinib mesylate

This article reports early blastic transformation of chronic myeloid leukemia (CML) in a child following a complete cytogenetic response induced by imatinib mesylate. A 14-year-old Japanese boy was diagnosed with t(9;22) cryptic CML in the chronic phase and treated with imatinib. His response to treatment was slow, but a major cytogenetic response was obtained at 142 days of therapy. However, he developed lymphoid blastic transformation at 9 months. He attained remission with acute lymphoblastic leukemia-type chemotherapy and then successfully received a non-T-cell-depleted allogeneic stem cell transplantation (allo-SCT) with his mother's two loci-mismatched donor cells. A sudden blastic transformation may occur even with a complete cytogenetic response induced by imatinib. CML patients who respond slowly to imatinib may still be candidates for allo-SCT, even when a major cytogenetic response is obtained.

Deletion of the 5'ABL region in Philadelphia chromosome positive chronic myeloid leukemia: frequency, origin and prognosis

The use of new nuclei probes in fluorescent in situ hybridization (FISH) at diagnosis and during follow up has recently allowed the detection of a deletion of the 5'abl region on the derivative chromosome 9 among some CML patients. This deletion seems to be a powerful and independent prognostic factor. The aim of our study was not only to estimate the frequency of the deletion of the 5'abl region among chronic myeloid leukemia (CML) patients with bcr-abl fusion gene, but also, to assess whether this deletion is concomitant with the formation of the Philadelphia (Ph) chromosome or represents a sign for progression of the disease, and finally to evaluate the prognostic implications of this abnormality. One hundred and twelve patients were analysed using FISH with LSI bcr-abl dual ES color probes, at the moment of the diagnosis when possible or, if not, on a sample with a strong rate of Ph+ metaphases evaluated by conventional cytogenetics. When the deletion was highlighted in a patient, we performed an hybridization on all the samples available during the follow-up. The deletion of the 5' region of the gene abl was detected among 9 patients. When the deletion was found in a patient, it was present in all the Ph+ metaphases and nuclei and in all the samples studied at diagnosis and during follow up. In these patients, we never identified cells carrying the Ph chromosome translocation without the deletion. None of the patients with the deletion had a major cytogenetic response to treatment with interferon. The deletion of the 5'abl region on der(9), present in approximately 9% of the CML, takes place at the same time as the formation of the Ph chromosome translocation and seems of worse prognosis. The detection of this deletion could thus constitute an argument to start STI treatment in first intent for these patients.

Detection of the BCR-ABL gene by interphase fluorescence in situ hybridization (iFISH) in chronic myelogenous leukemia patients after hemopoietic stem cell transplantation: the feasibility of iFISH monitoring of therapeutic response in peripheral blood

The detection of the Philadelphia (Ph) translocation has been accomplished primarily by cytogenetic analysis and reverse transcriptase polymerase chain reaction (RT-PCR). RT-PCR is highly sensitive (1/10(4)-10(6)) but not quantitatively reliable and is thus unsuitable for the monitoring of Ph-positive cells during therapy. Interphase fluorescence in situ hybridization (iFISH) allows analysis of a large number of cells (> 500) in a timely and efficiently quantitative manner. We obtained 118 peripheral blood (PB) and 127 bone marrow (BM) samples from 75 adult chronic myelogenous leukemia (CML) patients undergoing stem cell transplantation. We simultaneously performed nested RT-PCR and iFISH for all samples. False-positive cells were detected in 2.48% +/- 0.93% (mean +/- SD) of PB samples and 2.75% +/- 0.83% of BM samples. The iFISH results for PB and BM ranged from 1.4% to 92.8% and 1.0% to 93.8%, respectively. Correlation analysis of iFISH results for PB versus BM samples showed a strong relation (r = .993). A significant correlation (P < .05) was also found between iFISH and first-round RT-PCR. The sensitivity of BCR-ABL iFISH was similar to that of first-round RT-PCR, and iFISH results for PB and BM were also well correlated. Thus, iFISH analysis of PB and/or BM samples may be more clinically reliable than RT-PCR in the quantitative monitoring of BCR-ABL fusion in CML after transplantation.