The use of FISH with chromosome-specific repetitive DNA probes for the follow-up of leukemia patients. Correlations and discrepancies with bone marrow cytology

Evaluation of chromosome 5 aberrations in complex karyotypes of patients with myeloid disorders reveals their contribution to dicentric and tricentric chromosomes, resulting in the loss of critical 5q regions

Dicentric chromosomes have often been observed in complex karyotypes in previously reported studies of therapy-related myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Fluorescence in situ hybridization (FISH) has now made the characterization of these rearrangements much easier. Dicentric and tricentric chromosomes were identified in 21 patients (9 MDS and 12 AML) among the 133 consecutive MDS/AML patients (17%) who had a structural or numerical aberration of chromosome 5 using conventional cytogenetic analysis. One third (7/21) of the patients had received alkylating drugs for a previously diagnosed cancer or chronic myeloproliferative disease. Loss of 5q material was identified in all 21 patients. One copy of the EGR1 (5q31) or the CSF1R (5q33 approximately q34) genes was lost in 20 of the 21 patients. Dicentric and tricentric chromosomes involving chromosome 5 are frequently observed in complex karyotypes among patients with de novo or therapy-related MDS/AML. They lead to deletions of various parts of the long arm of chromosome 5.

Establishment and study of different real-time polymerase chain reaction assays for the quantification of cells with deletions of chromosome 7

The evaluation of residual disease, which has prognostic value in the treatment of hematological malignancies, is currently assessed by scoring a limited number of cells by karyotyping and molecular cytogenetics. Real-time polymerase chain reaction (PCR) is an easier and more sensitive technique, enables analysis of a larger number of cells, and decreases sampling error. However, real-time PCR has been applied only to target transcripts of fusion genes. Here, we considered two real-time PCR strategies to quantify a number of cells carrying a partial deletion of chromosome 7 mixed with normal disomic cells. The first strategy was based on the amplification of two sequences, one on chromosome 7 and the other on chromosome 14. In the second strategy residual disease was assessed by the ratio between the two alleles of a bi-allelic marker, mapped on chromosome 7, measured with allele-specific assays. Precision and accuracy of the two approaches were tested by reference samples with nominal values of residual disease ranging from 2 to 95%. As expected the second strategy resulted in more precise and accurate monitoring within the range from 5 to 95%. Furthermore, this method may be applied to assess the number of dysplastic or neoplastic clones carrying any unbalanced chromosome changes.

9q34 rearrangements in BCR/ABL fusion-negative acute lymphoblastic leukemia

The t(9;22)(q11.2;q34) translocation is found in a subset of acute lymphoblastic leukemia (ALL). The presence of this translocation involving the fusion of BCR/ABL genes represents a poor prognostic group. Because of the importance in detecting t(9;22) in ALL patients and because occasionally a cytogenetically cryptic BCR/ABL fusion is detected with fluorescence in situ hybridization (FISH), our laboratory routinely performs BCR/ABL FISH tests on all newly diagnosed ALL patients. In the past year, 25 consecutive, newly diagnosed, untreated ALL cases were analyzed. We report the cytogenetics and FISH findings of three cases containing a rearranged 9q34 region with an intact BCR (22q11.2) region and an absence of the BCR/ABL fusion. A split ABL signal representing a translocation of the 9q34 region with chromosome segments other than 22q11.2 (BCR) was observed in 3 cases. Two of these patients were 3 years old; one was 21 at the time of diagnosis. A split ABL FISH signal without the involvement of BCR does not represent a t(9;22) translocation, and prognostic implications of this apparent subgroup of ALL cases have not been determined. Cytogenetic, pathologic, and clinical aspects of these three cases are presented.

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.

A strategy to detect chromosomal abnormalities in children with acute lymphoblastic leukemia

Conventional cytogenetics (CC) can be used to identify chromosomal abnormalities that are predictors of treatment outcome in acute lymphoblastic leukemia (ALL). The detection of abnormalities in ALL is difficult because low mitotic index and poor-quality metaphases are obtained. Flow cytometry (FC) and fluorescence in situ hybridization (FISH) can be used to detect aneuploidy in any phase of the cell cycle, increasing the number of analyzable cells. The aim of this study was to develop a strategy combining these methods to improve the frequency of chromosome abnormality detection. One hundred children with newly diagnosed ALL were included. CC and DNA content analysis by FC were performed in all patients. The numerical abnormalities identified by both methods were compared and patients were classified as concordant or discordant. FISH was used to support aneuploidy results in discrepant cases using centromeric probes for the chromosomes most frequently involved in aneuploidy. CC and FC showed high concordance (86%). Fourteen cases were discrepant: nine showed hypodiploidy and low hyperdiploidy by cytogenetics and five showed high hyperdiploidy by FC. FISH confirmed aneuploidy in 12 cases in which it could be performed. High hyperdiploidy was the most common abnormality; the 31 cases showing this aneuploidy were identified by FC. The search for abnormalities must begin by measuring DNA content to detect this aneuploidy, which is useful to evaluate the patient's risk. However, it is important to screen for structural abnormalities by CC or molecular techniques. This strategy may detect chromosomal abnormalities, optimizing resources in laboratories where not all the screening methods are available.

Constitutional chromosome aberrations as pathogenetic events in hematologic malignancies

A predisposition to tumor development is associated with some constitutional chromosomal abnormalities. Investigations of families with an apparent hereditary cancer and constitutional chromosome rearrangements have led to the molecular identification of tumor suppressor genes. Under the somatic mutation theory for the development of cancer, two mutational events are required. The first step may be a constitutional event and the second an acquired genetic mutation. Cytogenetic studies were performed on 5633 bone marrow specimens from patients with hematologic malignancies from a single institution. Fifty cases of constitutional chromosome aberrations were detected. Data collected from the literature and from our series are reviewed and compared with the incidence of specific constitutional chromosome aberrations in the newborn population. Possible mechanisms that may predispose individuals with constitutional chromosome aberrations to the development of a hematologic malignancy are reviewed.

Treatment of leptomeningeal metastases evaluated by interphase cytogenetics

PURPOSE

Although cytologic examination of CSF is the primary method for the evaluation of response to therapy for leptomeningeal metastases (LMMs), the procedure's sensitivity decreases throughout the course of protracted therapy. We studied whether this response could be monitored more accurately through the detection of numerical chromosomal aberrations by interphase cytogenetics, using fluorescence in situ hybridization (FISH).

PATIENTS AND METHODS

Seven patients treated for LMMs and with a known numerical aberration for chromosome 1 in their pretreatment CSF were included in this study. Up to 16 consecutive CSF samples were analyzed by means of the fluorescence in situ hybridization (FISH) technique for cells with aberrant chromosome 1 content. The results of routine cytology and FISH analyses were compared and were correlated with each patient's neurologic status.

RESULTS

Routine cytology detected malignancies in only 24 of the 76 samples, all of which were classified as chromosomally abnormal by FISH (except for two samples that could not be evaluated). Moreover, FISH demonstrated aneusomic cells in 32 additional samples, which could therefore be classified as malignant. The FISH results correlated better with patient neurologic status in that more malignant cells were detected in the CSF of neurologically deteriorating patients.

CONCLUSION

Using FISH in addition to performing routine cytologic examination of CSF led to a more accurate evaluation of response to treatment in patients treated for LMMs.

Interphasic analysis of aneuploidy in cancer cell lines using primed in situ labeling

The primed in situ (PRINS) labeling technique has been adapted to chromosomal screening of interphasic tumoral cells. A panel of ten chromosome-specific alpha-satellite DNA primers was used to evaluate numerical chromosome abnormalities in two colon cancer cell lines (Caco-2 and HT-29) and in three of their subpopulations (PF11, TC7, and HT29-MTX). In each cell line, the copy number distribution for different chromosomes showed different patterns. The observation of significant variations in the chromosome constitutions between subpopulations derived from the same original tumor suggests the common occurrence of chromosome copy number heterogeneity in tumoral cell lines. This study demonstrates that the PRINS procedure offers a simple and reliable method for in situ chromosomal screening, which could be efficiently used for karyotypic analysis of tumoral cells.

Retrospective analysis of clonality and detection of residual disease in myeloid leukemia by FISH on long-term stored bone marrow smears

BACKGROUND

Fluorescence in situ hybridization (FISH) has allowed the detection of numerical chromosomal aberrations in interphase nuclei on fresh or frozen smears of leukemia.

METHODS

To analyze clonality and residual disease in myeloid leukemia retrospectively, we applied FISH to bone marrow smears stored at ambient temperature for up to 9 years.

RESULTS

When hybridization efficiency was investigated on stored control smears from patients without hematological malignancy, more than 96% of nuclei showed the expected number of signals using DNA probes specific for chromosome 7, X or Y. In combination with cell morphology, we observed much higher hybridization efficiency in blasts and granulomonocytic cells compared with lymphoid and erythroid cells. On the basis of good hybridization efficiency for old smear specimens, we applied FISH to stored bone marrow smears of myeloid leukemias, in which either loss of chromosome 7 or loss of sex chromosomes had been verified previously by conventional cytogenetics (one patient with chronic myelomonocytic leukemia (CMML) and four with acute myeloid leukemia (AML; three M2 and one M7)). As a result, the loss of chromosome was detected in blasts from all patients and was observed in mature granulocytes, except in M7. In the CMML patient and one AML (M2) patient with t(8;21), lymphoid and erythroid cells also showed the loss of chromosomes, suggesting that it should occur at stem-cell level. A high amount of residual disease was detected in the morphological remission samples in one AML (M2) patient after induction therapy. The patient eventually succumbed to relapse.

CONCLUSION

Thus, the present FISH technique is useful to analyze the clinical significance of clonality and the residual disease in myeloid leukemia, retrospectively.

Fluorescence in situ hybridization (FISH) detects clonal instability in an optic nerve relapse of acute lymphoblastic leukemia

PURPOSE

We report a case of an isolated optic nerve relapse 3.5 years after diagnosis of hyperdiploid acute lymphoblastic leukemia (ALL) in a 6-year-old boy who had been off treatment for 3 months. The use of interphase fluorescence in situ hybridization (FISH) for clonal identification of chromosome abnormalities is described.

PATIENT AND METHODS

An asymptomatic lesion over the right optic nerve head was identified on routine funduscopic exam. Fine needle aspiration of the optic nerve infiltrate provided tissue for morphologic, immunohistochemical, and FISH analyses.

RESULTS

FISH showed similar but not identical chromosome makeup of the leukemic blasts at the time of relapse as compared to tissue samples obtained at the time of diagnosis.

CONCLUSION

Despite antimetabolite therapy, hyperdiploid ALL can rarely recur isolated to an optic nerve. FISH is a useful adjunct for confirming relapse when low numbers of white blood cells are obtained with fine needle aspiration.