Monoallelic p53 deletion in chronic lymphocytic leukemia detected by interphase cytogenetics

Applications of Fluorescence In Situ Hybridization Technology in Malignancies

The molecular characterization of nonrandom recurrent cytogenetic abnormalities has identified numerous disease-related genes involved in hematologic and lymphoid malignancies. Cytogenetic analysis has become essential for disease diagnosis, classification, prognostic stratification, and treatment guidance. Fluorescence in situ hybridization (FISH) has greatly enhanced the field and enabled a more precise determination of the presence and frequency of genetic abnormalities. The advantages of FISH compared to standard cytogenetic analysis are that FISH can be used to identify genetic changes that are too small to be detected under a microscope, does not require cell culture, and can be applied directly on fresh or paraffin-embedded tissues for rapid evaluation of interphase nuclei. The application of FISH with a variety of chromosome-specific DNA probes helps to further define molecular subclasses and cytogenetic risk categories for patients with particular hematologic malignancies. FISH analysis is useful in identifying genetic abnormalities undetectable by conventional chromosomal analysis and monitoring residual disease during treatment and follow-up. Therefore, FISH has become an indispensable tool in the management of hematologic malignancies.

Impact of trisomy 12, del(13q), del(17p), and del(11q) on the immunophenotype, DNA ploidy status, and proliferative rate of leukemic B-cells in chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) is a well-defined clinical entity with heterogeneous molecular and cytogenetic features. Here, we analyze the impact of trisomy 12, del(13q), del(17p), and del(11q) as determined by interphase fluorescence in situ hybridization analysis of purified neoplastic B-CLL cells on their immunophenotype, DNA ploidy status and proliferative rate.Overall, 111 of 180 (62%) B-CLL cases studied displayed one (50%) or more (12%) genetic abnormalities, del(13q) (35%) being more frequently detected than trisomy 12 (23%) followed by del(11q) (9%) and del(17p) (8%). Trisomy 12 was associated with a higher frequency of DNA aneuploidy, stronger expression of CD19, CD20, CD22, CD24, CD27, CD79b, CD38, and sIg and lower reactivity for CD43 with respect to cytogenetically nonaltered cases. In turn, cases with del(13q) displayed greater reactivity for CD20, FMC7, CD27, CD22, CD5, and bcl2, while del(11q) was associated with brighter expression of CD38, FMC7, CD25, and sIg. Hierarchical clustering analysis of the immunophenotype of B-CLL cases with cytogenetic abnormalities allowed the identification of three different groups of patients with increasing frequencies of trisomy 12, del(11q), and del(13q). Remarkably, none of the cytogenetic abnormalities analyzed except coexistence of 13q- and 17p- had a clear impact on the proliferative index of B-CLL cells.

Analysis of a large multi-generational family provides insight into the genetics of chronic lymphocytic leukemia

We report the genetic analysis of a large multi-generational family composed of 144 individuals in which 11 members have been diagnosed with chronic lymphocytic leukaemia (CLL). The observation of a significant over-representation of monoclonal B-cell lymphocytosis (MBL) in unaffected family members strongly supports MBL being a surrogate marker of carrier status. A genome-wide linkage scan of the family using high-density 10K single nucleotide polymorphisms provided no significant evidence for a single gene model of disease susceptibility, inviting speculation that susceptibility to CLL has a more complex basis. The absence of a correlation in IGHV usage between affected family members does however argue strongly against exposure to a single super-antigen in disease development.

Diverse p53 gene aberration in hepatocellular carcinoma detected by dual-color fluorescence in situ hybridization

BACKGROUND AND AIM

In order to evaluate loss of the p53 gene more precisely, we performed dual-color fluorescence in situ hybridization (dual-color FISH) for chromosome 17 and p53 gene together with DNA polymorphism analysis of the p53 gene in hepatocellular carcinoma (HCC).

METHODS

Dual-color FISH using probes specific for the centromere of chromosome 17 and the p53 gene was performed for 41 HCC and DNA polymorphism analysis was also performed for them.

RESULTS

Of the 34 HCC tested by dual-color FISH, 20 had loss of at least one p53 gene (58.8%). In contrast, of the 32 HCC tested by DNA polymorphism analysis, 23 gave informative results, among which only eight had loss of heterozygosity (LOH) of the p53 gene (34.8%). Notably, among 14 cases positive for loss of the p53 gene by dual-color FISH, seven cases were negative for LOH of the p53 gene. Moreover, dual-color FISH revealed that the percentage of cells that lost at least one p53 gene increased as the HCC became less differentiated (P < 0.01), whereas LOH did not reveal any such correlation.

CONCLUSIONS

These data suggest that loss of the p53 gene was present in a considerable number of HCC, and diversity of the p53 gene aberration increases with progression of HCC. Dual-color FISH is an effective method for detection of p53 gene aberration, and it can provide new insight into oncogenesis in HCC.

Molecular differences between small and large cells in patients with chronic lymphocytic leukemia

The genetic events involved in the transformation of chronic lymphocytic leukemia (CLL) to Richter's syndrome (RS) are poorly understood. Frequently large cells are seen in the bone marrows of patients with CLL and evidence of RS. Using a laser-capture microdissection we analyzed small and large leukemic bone marrow cells from 19 patients with RS for loss of heterozygosity (LOH) on chromosome 11 (D11S2179 at the ATM gene), 17 (D17S938 and D17S1852 at the TP53 site), and 20 (Plc1, D20S96, D20S110, and D20S119). Megakaryocytes were also isolated and used as a control for normal cells. Four of 15 (27.7%) informative cases showed LOH in small cells in the ATM gene while seven (46.7%) showed LOH in large cells. Six of 15 (40%) informative cases had LOH in chromosome 17 in small cells, and eight (53%) showed LOH in large cells. Eleven of 19 informative cases (61.1%) showed LOH in chromosome 20 in large cells, and eight (42.1%) showed LOH in small cells. RS cases with LOH at chromosome 20 were associated with marginally shorter survival rates (P = 0.08). Our data suggest that there are significant molecular differences between large and small cells in patients with CLL. Further analysis of the genes on these chromosomes may provide new insight into our understanding of the transformation of small CLL cells to large (Richter) cells.

Interphase fluorescence in situ hybridization analysis of del(11)(q23) and del(17)(p13) in chronic lymphocytic leukemia. a study of 40 early-onset patients

Although B-cell chronic lymphocytic leukemia (B-CLL) is the most common form of leukemia in Western countries, little is known about its underlying molecular abnormalities and their prognostic significance, particularly for use in early therapeutic interventions in young patients. As TP53 tumor suppressor gene abnormalities and 11q23 deletions are reported to be prognostically adverse in hematologic malignancies, we used interphase fluorescence in situ hybridization to analyze their incidence and prognostic significance in young B-CLL patients. Bone marrow samples from 40 untreated B-CLL patients at diagnosis were studied using five yeast artificial chromosome clones from the 11q23.1 approximately q23.3 chromosomal region and a probe specific for the 17p13.1 locus. Twenty-three patients (58%) carried 11q deletions. Interestingly, 16 of 17 patients (94%) who showed early disease progression exhibited this chromosomal abnormality, suggesting that 11q deletions may help to identify more aggressive disease in early stage patients. In contrast, monoallelic TP53 deletions were found in all of the patients. The TP53 and 11q deletions were only present in a proportion of the clonal B-cells, which suggests that they are secondary events in B-CLL.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.

Molecular abnormalities in B-cell chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia is the commonest adult leukaemia, however the pathogenesis is largely unknown. Since the 1980s specific chromosomal abnormalities have been identified, of which the commonest are deletions of chromosomes 6q, 11q23, 13q14 and 17q13 and trisomy 12. The search for the responsible oncogenes at these sites has proved to be extremely frustrating. There are many oncogenes at 11q23 but the exact gene(s) responsible have yet to be identified. Germline abnormalities of the ATM gene occur in about 18% of patients compared to a normal population carriage of 0.5% but not all studies agree that ATM is the gene responsible. Unfortunately, despite the identification of various minimally deleted regions and the full sequencing of 13q14 no oncogenes have been identified. All original studies suggested the presence of a autosomally recessive tumour suppressor gene at this site but more recent studies suggest this may not be the case and the pathogenesis is more complex than first thought. Similarly, no genes have been identified at 6q or on chromosome 12. We know that the p53 tumour suppressor gene at 17p13 is an important prognostic indicator but it occurs in a minority of patients (about 15%), usually in patients with advanced disease, and therefore probably is not of aetiological importance.

Dicentric (17;18) in a case of atypical B-cell chronic lymphocytic leukemia

We report a new dic(17;18)(p11.2;p11.2) in a 61-year-old male patient diagnosed with atypical B-cell chronic lymphocytic leukemia. The dic(17;18)(p11.2;p11.2) was detected in 90%, 10%, and 100% of metaphases in the peripheral blood, bone marrow, and lymph node, respectively. Fluorescence in situ hybridization studies with chromosome 17 and 18 centromeric probes revealed the presence of two normal centromeres of both chromosomes 17 and 18. The centromere of one chromosome 17 was found together with the centromere of one chromosome 18, confirming the dicentric nature of the rearrangement. In addition, with the use of a 17p13.1 region probe, monosomy of the 17p13 region, where the Tp53 gene is located, was observed.

TP53 deletions but not trisomy 12 are adverse in B-cell lymphoproliferative disorders

Abnormalities of the TP53 tumor suppressor gene at 17p13.1 are prognostically adverse in a variety of hematolymphoid malignancies. The present study utilized interphase fluorescence in situ hybridization (I-FISH) to detect TP53 deletions and trisomy 12 in 101 clinical specimens from 98 patients with B-cell lymphoproliferative disorders (B-LPDs). Twelve patients had TP53 deletions (group A), 23 had trisomy 12 (group B), and 63 had neither (group C). The groups did not significantly differ in age, duration of disease, absolute lymphocyte count, or percentage with an immunophenotype or cytology atypical for chronic lymphocytic leukemia (CLL). The clinical stage of disease and lactate dehydrogenase (LDH) level were higher in group A, with less response to therapy. After a median follow-up of 19 months, seven of the patients in group A had died of disease (another patient subsequently has had large cell transformation) compared with none in group B and nine in group C. Multivariate analysis found the stage of disease and TP53 deletions as the only parameters independently associated with shortened survival (P < 0.001). Thirty-nine patients had conventional cytogenetic analysis (CCA) which was complexly abnormal in 11 patients; 6 of whom died of disease. There was a trend for complex cytogenetics to be seen more frequently in group A, often with 17p involvement. For most laboratories, CCA may be the preferable initial study to identify prognostically different subgroups of B-LPDs. However, as more probes and clinical outcome data become available, I-FISH will likely play an increasingly important ancillary role.

CD5 B cells and B-cell malignancies

Over the past year, progress has been made in understanding of the physiology and disease associations of CD5+ (B1) B cells, although their exact role in pathogenesis remains unclear. Earlier studies on the negative function of CD5 within the B-cell receptor complex have been substantiated, and it seems likely that soon the signaling pathways used by this coreceptor will be elucidated. Progress in diagnosis, physiology, and etiopathogenesis of CD5+ malignancies has been made, particularly in B-cell chronic lymphocytic leukemia. The low-level expression of surface immunoglobulin has been explained by the mutations that occur in the associated CD79b. Two new potential tumor-suppressor genes have been identified in the hot spot of chromosome 13q, which provides an exciting step forward in understanding of the etiopathogenesis of some B-cell chronic lymphocytic leukemia. Activated signal transducers for activation of transcription factors molecules have been shown to be phosphorylated on different amino acids in B1 and chronic lymphocytic leukemia tumors, although the significance of this is, as yet, unclear. Finally, aberrant expression of CD40L by chronic lymphocytic leukemia T cells may contribute to the immunodeficiency that develops in these patients.

Replication pattern in cancer: asynchronous replication in multiple myeloma and in monoclonal gammopathy

In this study we evaluated the replication pattern and cell-cycle dynamics of cells from patients considered to have a premalignant condition (monoclonal gammopathy, or MGUS) and patients with multiple myeloma (MM), as well as healthy controls. We applied the fluorescence in situ hybridization (FISH) technique with the TP53, RB-1 and 21q22 loci on the patient's cells. Asynchrony was determined by the presence of one single and one set of double dots in the same cell. The rate of asynchronic replication was significantly higher in the cells from MM patients, with intermediate value in the cells from MGUS, while the lowest rate was in cells from controls. We suggest that these results may reflect the changes in gene replication and cell-cycle progression that occur in premalignant and malignant cells.