The impact of molecular cytogenetics on chronic lymphoid leukaemia

Relevance of IgVH gene somatic hypermutation and interphase cytogenetics in lymphomatous presentation of chronic lymphocytic leukemia/small lymphocytic lymphoma

BACKGROUND

Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are regarded as the same entity, with SLL restricted to tissue cases featuring no leukemic phase. In this study, the authors evaluate a group of SLL cases for cytogenetic abnormalities and IgVH gene mutational status to illicit differences between CLL and SLL.

DESIGN

IgVH gene polymerase chain reaction amplification and subsequent sequencing were preformed on formalin-fixed, paraffin-embedded archival tissue of 44 patients (SLL n = 34 or CLL n = 10). Cytogenetic data, CD38, and ZAP-70 expression were also evaluated for these cases.

RESULTS

The data indicate that 9/34 (26%) SLL cases have somatic hypermutation >2%, which is less than the CLL group where 40% were mutated (4/10). Cytogenetic abnormalities were seen in 58% of the SLL cases with many showing abnormalities associated with favorable to intermediate prognosis.

CONCLUSION

The authors' attempt to compare CLL with SLL with regards to cytogenetic and IgVH mutational status shows no statistically significant difference.

Translocation (8;14)(q24;q32) as the sole cytogenetic abnormality in B-cell prolymphocytic leukemia

B-cell prolymphocytic leukemia is a relatively rare lymphoproliferative disorder. No specific cytogenetic abnormality has yet been associated with it. The most common translocation reported in patients with this disease is t(11;14)(q13;q32). We describe the case of a patient with B-cell prolymphocytic leukemia and a hitherto unreported genetic translocation (8;14)(q24;q32) as the sole genetic abnormality, classically seen in patients with B-cell acute lymphoblastic leukemia/Burkitt lymphoma. This patient presented with an asymptomatic leukocytosis and splenomegaly. Her marrow showed lymphoid hyperplasia, with immunophenotyping consistent with prolymphocytic leukemia; however, t(8;14)(q24;q32) was the only cytogenetic aberration with both standard karyotyping and fluorescence in situ hybridization analysis.

P2X7 polymorphism and chronic lymphocytic leukaemia: lack of correlation with incidence, survival and abnormalities of chromosome 12

The P2X7 receptor, a plasma membrane ATP-gated ion channel that plays a role in lymphocyte apoptosis, has been suggested as an important contributory factor to the pathogenesis of chronic lymphocytic leukaemia (CLL). The P2X7 gene resides on chromosome 12 and is polymorphic in the population at large (1513A/C) with the A and C alleles encoding fully active and nonfunctional proteins, respectively. We have evaluated the significance of this polymorphism by genotyping 144 patients with CLL and 348 healthy controls using a tetraprimer ARMS assay. We found no significant difference in allele frequency between patients and controls. Although patients with the C allele (A/C heterozygotes or C/C homozygotes) had a marginally shorter survival than those who were homozygous for the A allele, this difference was not significant for either the patient group considered as a whole or for IgVH-mutated/unmutated subsets. Finally, no association was found between trisomy 12 and P2X7 genotype. We conclude that the influence, if any, of P2X7 genotype on susceptibility to CLL or clinical outcome is small.

Update in the pathologic features of mature B-cell and T/NK-cell leukemias

Modern diagnosis of mature B- and T-cell leukemias requires integration of morphologic, immunophenotypic, and molecular genetic features. This integrative approach has allowed more precise definitions of specific disease entities. This in turn provides better information for clinicians to select proper therapy and determine prognosis. The characteristic pathologic features of these disorders are reviewed.

Chromosome anomalies detected by interphase fluorescence in situ hybridization: correlation with significant biological features of B-cell chronic lymphocytic leukaemia

Fluorescence in situ hybridization (FISH) was used to detect 6q-, 11q-, +12, 13q-, 17p- and translocations involving 14q32 in interphase nuclei from blood and/or bone marrow from 113 patients with B-cell chronic lymphocytic leukaemia (B-CLL). A total of 87 patients (77%) had a FISH anomaly: 13q- x 1 was most frequent (64%) followed by 13q- x 2 (28%), +12 (25%), 11q- (15%), 17p- (8%) and 6q- (0%). FISH results for blood and bone marrow cells in 38 patients were similar. Purified CD5+/CD19+ cells from blood were studied in eight patients and results indicate that in some patients not all B cells have FISH anomalies. We used a defined set of hierarchical FISH risk categories to compare FISH results by stable versus progressive disease, age, sex, Rai stage, CD38+ expression and IgVH mutational status. Significant differences in FISH risk distributions were associated with Rai stage, disease status and CD38+, but not by age, sex or IgVH mutational status. To look for baseline factors associated with high-risk disease, multivariate analysis of age, sex, Rai stage, CD38+ and disease status versus FISH risk category was performed. Importantly, only CD38+ was significantly associated with high-risk FISH categories (+12, 11q- and 17p-) after adjustment for the effects of other variables.

Cytogenetic and FISH studies in myelodysplasia, acute myeloid leukemia, chronic lymphocytic leukemia and lymphoma

Conventional cytogenetic studies are widely used today to diagnose and manage patients with hematological malignancies. The application of fluorescence in situ hybridization (FISH) with chromosome-specific DNA probes helps to further define molecular subclasses and cytogenetic risk categories for patients with these disorders. Moreover, FISH permits analysis of proliferating (metaphase cells) and non-proliferating (interphase nuclei) cells, and is useful in establishing the percentage of neoplastic cells before and after therapy (minimal residual disease). For patients with myelodysplasia or acute myeloid leukemia, these chromosome techniques are important for accurate diagnosis and classification of disease and to help decide treatment and monitor response to therapy. Conventional cytogenetic studies have been problematic in chronic lymphocytic leukemia because the neoplastic cells divide infrequently. However, interphase FISH studies now permit detection of chromosome anomalies with prognostic significance in chronic lymphocytic leukemia. The World Health Organization recognizes that genetic anomalies are one of the most reliable criteria for classification of malignant lymphomas. New methods to extract individual nuclei from paraffin-embedded tissue are now available which permit the use of interphase FISH to detect important chromosome anomalies in lymphoma.

Four novel non-random chromosome rearrangements in B-cell chronic lymphocytic leukaemia: 6p24-25 and 12p12-13 translocations, 4q21 anomalies and monosomy 21

Nine patients with previously unreported chromosome changes were identified among 209 B-cell chronic lymphocytic leukaemia (CLL) cases: three patients had a translocation involving 6p24-25; three had a 12p12-13 translocation; two had 4q21 involvement (one with coexisting 6p anomaly); and two had monosomy 21. Interphase fluorescence in situ hybridization (FISH) detected some cryptic aberrations (+12, 6q-, 17p-, 11q-) in those patients with 6p translocations, whereas only a cytogenetically undetected 13q14 deletion was found in the remaining cases. Atypical morphology was noted in six cases, including both cases with monosomy 21, two cases with 6p and 4q21 anomaly and one case with 12p involvement. Four of these cases also had more than one phenotype deviation with respect to the classical CLL phenotype. Disease progression after 21-51 months (median 41) was noted in two cases with 6p and 4q21 involvement and in one case with 12p anomaly and monosomy 21. We arrived at the following conclusions: (i) 6p24-25 and, possibly, 4q21 lesions represent non-random events in CLL, occurring in association with other well-known unbalanced rearrangements; (ii) 12p rearrangements and monosomy 21 may possibly represent early chromosome defects that are not associated with the classical DNA gains and losses known to be present in the majority of CLL; and (iii) atypical morphology and immunophenotype as well as disease progression were frequently observed in these cases

p53 gene deletion and trisomy 12 in hairy cell leukemia and its variant

The deletion or mutation of the p53 tumour suppressor gene on chromosome 17p13 is known to be associated with aggressive disease in several B-cell malignancies. The present study describes the p53 gene status in 20 cases of hairy cell leukemia (HCL) and in 12 cases of its morphological variant (HCL-V) by fluorescence in situ hybridization (FISH). A high incidence of p53 deletion was found in both diseases (75-100% of cases). However, a significant difference was observed between the proportion of cells with p53 deletion in HCL-V cases (mean 31%) and HCL cases (mean 12%) P value < 0.01. The observed difference correlates with the well known tendency for transformation and poor response to therapy in HCL-V and seven cases of HCL-V with greater than 22% of cells with p53 deletion showed features of disease progression and transformation. Trisomy 12 was present in 8.5% of the cells in one case of HCL-V and in 6-8% of cells in three cases of HCL.

Chromosomal imbalances in primary lymphomas of the central nervous system

Twenty-two primary central nervous system lymphomas of immunocompetent adults were studied by comparative genomic hybridization. All were high-grade diffuse large B cell lymphomas. Comparative genomic hybridization revealed an average of 5.5 chromosomal changes per tumor, with gains being more common than losses (3.5 vs. 2.0). The most frequent DNA copy number changes were gains on chromosomes 1, 12, 18 (41% each), 7 (23%), and 11 (18%) and losses involving chromosomes 6 (59%), 18, and 20 (18% each). Commonly involved regions were +12q (41%), +18q (36%), +1q (32%), and +7q (23%), as well as -6q (50%), -6p (18%), -17p, and -18p (14% each). High-level gains were found on 7 chromosomes, mainly involving chromosomes 18q (23%), 12q (18%), and 1q (14%). Minimal common regions of over- and underrepresentation were found on +1q25-31, -6q16-21, +7q11.2, +12p11.2-13, +12q12-14, +12q22-24.1, and +18q12.2-21.3. A significant correlation between loss of DNA copy numbers on chromosome 6q and shorter survival could be established (10.2 vs. 22.3 months; P < 0.05). Our findings suggest that chromosomal imbalances of primary central nervous system lymphomas are similar to those of diffuse large B cell lymphomas at other locations and are probably not related to cerebral presentation; however, they may be prognostically relevant.