Effect of conditioned medium, nutritive elements and mitotic synchronization on the accuracy of the cytogenetic analysis in patients with chronic myeloid leukemia at diagnosis and during alpha-interferon therapy

Chronic myeloid leukemia: cytogenetic methods and applications for diagnosis and treatment

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disease caused by recombination between the BCR gene on chromosome 22 and the ABL1 gene on chromosome 9. This rearrangement generates the BCR-ABL1 fusion gene that characterizes leukemic cells in all CML cases. In about 90% of cases, the BCR-ABL1 rearrangement is manifest cytogenetically by the Philadelphia (Ph) chromosome, a derivative of the reciprocal translocation t(9;22)(q34;q11.2). For the remaining cases, recombination may be more complex, involving BCR, ABL1, and genomic sites on one or more other chromosomal regions, or it may occur cryptically within an apparently normal karyotype. Detection of the Ph and associated t(9;22) translocation is a recognized clinical hallmark for CML diagnosis. The disease has a natural multistep pathogenesis, and during chronic phase CML, the t(9;22) or complex variant is usually the sole abnormality. In 60-80% of cases, additional cytogenetic changes appear and often forecast progression to an accelerated disease phase or a terminal blast crisis. Because new frontline therapies such as imatinib specifically target the abnormal protein product of the BCR-ABL1 fusion gene to eliminate BCR-ABL1 positive cells, there is a new reliance on the cytogenetic evaluation of bone marrow cells at diagnosis, then at regular posttreatment intervals. Combined with other parameters, presence or absence of Ph-positive cells in the bone marrow is a powerful early indicator for clinical risk stratification. Cytogenetic changes detected at any stage during treatment, including in the BCR-ABL1-negative cells, may also provide useful prognostic information. Laboratory methods detailed here extend from initial collection of peripheral blood or bone marrow samples through cell culture with or without synchronization, metaphase or interphase harvest, hypotonic treatment and fixation, slide preparation for G-banding or fluorescent in situ hybridization (FISH), and final interpretation.

Automated four-color interphase fluorescence in situ hybridization approach for the simultaneous detection of specific aneuploidies of diagnostic and prognostic significance in high hyperdiploid acute lymphoblastic leukemia

In high hyperdiploid acute lymphoblastic leukemia (ALL), the concurrence of specific trisomies confers a more favorable outcome than hyperdiploidy alone. Interphase fluorescence in situ hybridization (FISH) complements conventional cytogenetics (CC) through its sensitivity and ability to detect chromosome aberrations in nondividing cells. To overcome the limits of manual I-FISH, we developed an automated four-color I-FISH approach and assessed its ability to detect concurrent aneuploidies in ALL. I-FISH was performed using centromeric probes for chromosomes 4, 6, 10, and 17. Parameters established for nucleus selection and signal detection were evaluated. Cutoff values were determined. Combinations of aneuploidies were considered relevant when each aneuploidy was individually significant. Results obtained in 10 patient samples were compared with those obtained with CC. Various combinations of aneuploidies were identified. All clones detected by CC were observed also by I-FISH, and I-FISH revealed numerous additional abnormal clones in all patients, ranging from < or =1% to 31.6% of cells analyzed. We conclude that four-color automated I-FISH permits the identification of concurrent aneuploidies of potential prognostic significance. Large numbers of cells can be analyzed rapidly. The large number of nuclei scored revealed a high level of chromosome variability both at diagnosis and relapse, the prognostic significance of which is of considerable clinical interest and merits further evaluation.

Application of growth factor stimulants improves cytogenetic analysis of chronic myeloproliferative disorder patients without alteration to cell lineage or clonality

Conventional cytogenetic methods rely on culturing bone marrow aspirates to obtain suitable and sufficient mitotic figures for G-banded analysis. Samples from patients with chronic myeloproliferative disorders (CMPD) often have increased failure rates due to reduced growth and poor morphology, all of which hamper the conventional karyotyping investigation. The application of growth factor (GF) stimulants to bone marrow aspirates has been shown to yield significant increases in both the quality and quantity of bone marrow metaphases obtained in 53 CPMD patient samples. All cultures were stimulated using the conditioned supernatant from the human bladder carcinoma cell line 5637, which contains IL-3, IL-6, and G-CSF. Results were assessed qualitatively on G-banded preparations and quantitatively by mitotic index (MI = % dividing cells). To assess whether the application of GF stimulants leads to clonal selection, culture samples from 15 patients were analyzed by fluorescence in situ hybridization, which supported the theory that clonal selection remains unaltered in GF-stimulated cultures. In addition to this immunophenotyping of cells, we demonstrated the lineage of cells propagated under these conditions. Cell markers were chosen to characterize B-lymphoid, T-lymphoid, myeloid, and primitive cell types. Results indicated that T cells were maintained in culture and B-lymphoid markers remained negative. In the myeloid subset, there was an overall reduction in the pan-myeloid markers. We believe this represents the loss of terminally differentiated cells (e.g., neutrophils) in culture. Overall, the study clearly demonstrates that the application of GF stimulants does not alter clonality or cell lineage propagated in these samples and is therefore suitable for application in diagnostic cytogenetic laboratories.

Polysomy 8 defines a clinico-cytogenetic entity representing a subset of myeloid hematologic malignancies associated with a poor prognosis: report on a cohort of 12 patients and review of 105 published cases

Tetrasomy, pentasomy, and hexasomy 8 (polysomy 8) are relatively rare compared to trisomy 8. Here we report on a series of 12 patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or myeloproliferative disorder (MPD) associated with polysomy 8 as detected by conventional cytogenetics and fluorescence in situ hybridization (FISH). In an attempt to better characterize the clinical and hematological profile of this cytogenetic entity, our data were combined with those of 105 published patients. Tetrasomy 8 was the most common presentation of polysomy 8. In 60.7% of patients, polysomy 8 occurred as part of complex changes (16.2% with 11q23 rearrangements). No cryptic MLL rearrangements were found in cases in which polysomy 8 was the only karyotypic change. Our study demonstrates the existence of a polysomy 8 syndrome, which represents a subtype of AML, MDS, and MPD characterized by a high incidence of secondary diseases, myelomonocytic or monocytic involvement in AML and poor overall survival (6 months). Age significantly reduced median survival, but associated cytogenetic abnormalities did not modify it. Cytogenetic results further demonstrate an in vitro preferential growth of the cells with a high level of aneuploidy suggesting a selective advantage for polysomy 8 cells.

Systematic screening at diagnosis of −5/del(5)(q31), −7, or chromosome 8 aneuploidy by interphase fluorescence in situ hybridization in 110 acute myelocytic leukemia and high-risk myelodysplastic syndrome patients: concordances and discrepancies with conventional cytogenetics

To assess the contribution of interphase fluorescence in situ hybridization (I-FISH) toward the detection of recurring unbalanced chromosomal anomalies at diagnosis, a systematic screening of -5/del(5)(q31), -7, and chromosome 8 aneuploidy was performed on 110 patients with acute myelocytic leukemia or high-risk myelodysplastic syndrome. We searched for monosomy 5/del(5q) by one-color I-FISH with a probe specific for the 5q31 region and for -7/8 by dual-color I-FISH with centromeric probes for chromosomes 7 and 8. Discrepancies between conventional cytogenetics (CC) and I-FISH were observed in 8 of the 110 patients (7.3%). For -5/del(5)(q31), a discordance was observed in two patients with complex abnormalities involving chromosome 5. Whereas no discordance was observed for -7, I-FISH detected a trisomy 7 unnoticed by CC in two cases. In six patients, I-FISH revealed a chromosome 8 aneuploidy not detected by CC. Our results illustrate that, when using this specific set of probes, I-FISH is of special interest for the detection of minor clones with chromosome 8 aneuploidy, breakpoint assessment, and sequence identification (markers). Also, to avoid misinterpretations, I-FISH should not be used alone at disease presentation, particularly in cases complex changes that have clearly established prognostic significance.

Determination of cutoff values to detect small aneuploid clones by interphase fluorescence in situ hybridization: the Poisson model is a more appropriate approach. Should single-cell trisomy 8 be considered a clonal defect?

We applied a dual-color interphase in situ fluorescence hybridization (I-FISH) technique using centromeric probes specific to chromosomes 7 and 8 on 20 control samples in order to define the statistical model best suited to determine cutoff values for detection of small abnormal clones. We found that the Poisson model is a more appropriate approach than a Gaussian model. Then, based on the analysis of 91 samples from 80 patients with myelocytic malignant hemopathies and either clonal or nonclonal -7 or +8 as determined with conventional cytogenetics (CC), we compared the respective power of I-FISH and CC for detection of aneuploidy, with special emphasis on the potential contribution of I-FISH as a complement to CC in the case of small abnormal clones. The I-FISH results were positive in samples with clonal -7 or +8 according to CC analysis. Whereas I-FISH was negative in samples with nonclonal -7 according to CC, thus confirming the reliability of the criteria used to define the clonality of -7; the situation was different with nonclonal +8. I-FISH revealed the clonality of +8 in most samples with single-cell +8. In several cases, however, the unquestionable clonal nature of +8, as evidenced during follow-up, could not be established with either CC or I-FISH according to accepted criteria. Our data suggest that, in case of a single metaphase with +8, the general rule should be amended and the single-cell +8 should be considered and reported as potentially clonal.

A novel BCR-ABL transcript e2a2 in a chronic myelogenous leukaemia patient with a duplicated Ph-chromosome and monosomy 7

A novel BCR-ABL transcript was detected by multiplex RT-PCR in a patient with Philadelphia chromosome (Ph) positive chronic myelogenous leukaemia (CML) in accelerated phase. Sequencing of the aberrant transcript revealed an in-frame e2a2 fusion that included a 9 basepairs insertion. Cytogenetic analysis showed t(9;22), an additional Ph chromosome and monosomy 7. The clinical course was dismal: therapy was poorly tolerated, and the patient died in blast crisis 10 months after diagnosis. These data support the association of additional Ph and monosomy 7 with poor prognosis and suggest that the novel e2a2 BCR-ABL transcript may be related to an aggressive clinical course.