Cytogenetic evidence for clonal evolution in B-cell chronic lymphocytic leukemia

Clonal evolution in chronic lymphocytic leukemia is scant in relapsed but accelerated in refractory cases after chemo(immune)therapy

Clonal evolution is involved in the progression of chronic lymphocytic leukemia (CLL). In order to link evolutionary patterns to different disease courses, we performed a long-term longitudinal mutation profiling study of CLL patients. Tracking somatic mutations and their changes in allele frequency over time and assessing the underlying cancer cell fraction revealed highly distinct evolutionary patterns. Surprisingly, in long-term stable disease and in relapse after long-lasting clinical response to treatment, clonal shifts are minor. In contrast, in refractory disease major clonal shifts occur although there is little impact on leukemia cell counts. As this striking pattern in refractory cases is not linked to a strong contribution of known CLL driver genes, the evolution is mostly driven by treatment-induced selection of sub-clones, underlining the need for novel, non-genotoxic treatment regimens.

First-line treatment of chronic lymphocytic leukemia: role of alemtuzumab

The CD52-targeting antibody alemtuzumab is established in clinical practice with convincing activity in relapsed and refractory chronic lymphocytic leukemia (CLL), particularly in patients with high-risk features and adverse prognosis. In the CAM307 study alemtuzumab was tested and finally approved as a first-line single agent, even though the hurdle with chlorambucil as the contender was not set very high. Within clinical trials, the drug demonstrated an excellent ability to eliminate minimal residual disease in blood and bone marrow, which has been correlated with a corresponding survival advantage in patients. However, in the maintenance setting, infectious complications due to severe T cell suppression have been highlighted and do not allow clinicans to use alemtuzumab outside of clinical trials. This review discusses potential therapeutic niches and future applications of alemtuzumab with a focus on CLL front-line treatment.

Genetic imbalances in progressed B-cell chronic lymphocytic leukemia and transformed large-cell lymphoma (Richter's syndrome)

Chromosomal imbalances were examined by comparative genomic hybridization in 30 cases of B-cell chronic lymphocytic leukemia (CLL) at diagnosis, in sequential samples from 17 of these patients, and in 6 large B-cell lymphomas transformed from CLL [Richter's syndrome (RS)] with no available previous sample. The most common imbalances in CLL at diagnosis were gains in chromosome 12 (30%), and losses in chromosomes 13 (17%), 17p (17%), 8p (7%), 11q (7%), and 14q (7%). The analysis of sequential samples showed an increased number of chromosomal imbalances in 6 of 10 (60%) patients with clinical progression and in 2 patients with stable stage C disease. No karyotypic evolution was observed in four cases with stable stage A disease and in one RS clonally unrelated to the previous CLL. Gains of 2pter, and 7pter, and losses of 8p, 11q, and 17p were recurrent alterations associated with karyotype progression. RS showed a higher number of gains, losses, total alterations, and losses of 8p and chromosome 9 than CLL at diagnosis. 17p losses were associated with p53 gene mutations and with a significantly higher number of chromosomal imbalances than tumors with normal chromosome 17 profile. However, no relationship was observed between 9p deletions and p16(INK4a) gene alterations. Losses of 17p and an increased number of losses at diagnosis were significantly associated with a shorter survival. These findings indicate that CLL has frequent chromosomal imbalances, which may increase during the progression of the disease and transformation into large cell lymphoma. Genetic alterations detected by comparative genomic hybridization may also be of prognostic significance.

High-grade transformation of low-grade non-Hodgkin's lymphomas: mechanisms of tumor progression

In the natural history of low-grade non-Hodgkin's lymphomas (NHL) a prolonged indolent phase of the disease may be followed by clinical progression toward intermediate and high-grade disease. The abrupt appearance of diffuse large cell lymphoma (DLL) in patients with low-grade NHL is usually associated with an accelerated clinical course and shorter time of survival. The histologic transformation has been described for chronic lymphocytic leukemia or small lymphocytic lymphoma (CLL/SLL), follicular lymphoma (FL), mantle cell lymphoma (MCL) and lymphoma of mucosa-associated lymphoid tissue (MALT). Although the histological transformation of low-grade lymphomas are relatively frequent, the clonal relationship between the two neoplasms and pathogenetic mechanisms underlying the progression of the disease are widely debated. In this review, we will focus on the possible relationship between the low-grade and the transformed high-grade NHLs and genetic lesions that may be associated with the histologic transformation and clinical progression of the disease.

Tumor suppressor genes and clonal evolution in B-CLL

This review highlights the genetic alterations that have been detailed in the malignant B-cell clones of patients with B-chronic lymphocytic leukemia (CLL). In particular, the alterations seen in p53 and the retinoblastoma (Rb) genes are reviewed. In addition, the multiplicity of cytogenetic alterations observed at baseline and on sequential analysis are summarized. The cytogenetic and molecular biologic analysis of B-CLL clones has revealed that there is a dynamic array of genetic events which occur within a B-cell clone. This latter data strongly suggests that clonal evolution may occur in B-CLL patients. However the relationship of the clonal instability to the patient's clinical course is still unclear. The relatively frequent detection of multiple tumor suppressor gene alterations in the B-CLL clones offer several interesting clues regarding the transformation event within B-CLL. A model is proposed which attempts to explain the potential contribution and interaction of p53 and Rb gene alterations in a malignant B-cell transformation.

Cytogenetic study of two cases with lymphoma of mucosa-associated lymphoid tissue

Cytogenetic studies have been reported in fewer than 20 patients with lymphoma of mucosa associated lymphoid tissue (MALT). Two patients with this disease at the Clinical Center, National Institutes of health had numerical and structural chromosome abnormalities, including +12 in both cases. The clonal karyotypes observed were 48-49,XX,t(2;8)(q33;p23), +3, -10,del(10)(q23), +12, +18 [cp] and 47,X,-X,i(6p), +7, +inv(12)(p13q13). Review of cytogenetic studies from published data showed that all cases of MALT lymphoma reported to date also have both numerical and structural chromosome abnormalities, the most frequent being numerical involvement of chromosomes 3, 7, and 12. Identification of a clonal abnormality can help establish the diagnosis when differential diagnosis includes atypical hyperplasia. Although trisomy 12 has been associated with a poor prognosis in B-cell chronic lymphocytic lymphoma (B-CLL), both these patients with MALT lymphoma have had long survival: 8 and 11 years, respectively.

Cytogenetic studies in patients with Richter's syndrome

Cytogenetic studies in six patients with Richter's syndrome (RS) showed complex chromosome abnormalities and chromosomal instability in five. No specific chromosomal abnormality was detected. Chromosomes 14 and 11 were the most frequently involved. Neither deletion of 13q14 nor complete trisomy 12 was observed. Two patients had structural rearrangement of 12q with t(5;12)(q21-q22;q23-q24). The involvement of this region of chromosome 12 may be significant, although not specific for chronic lymphocytic leukemia. These results were compared to those found in cytogenetically studied RS patients from the literature.

Cytogenetics in CLL and related disorders

Chromosome analysis of more than 1200 patients with chronic lymphocytic leukaemia reported to the International Working Party on Chromosomes in CLL and in the literature is analysed. Clonal chromosomal abnormalities are found in about half of the patients, and one third of those with clonal aberrations have trisomy 12, with or without additional changes. The most common structural abnormalities involve the long arm of chromosome 13, usually as deletions involving 13q14, the site of the retinoblastoma gene. Other recurrent abnormalities are deletions of the long arms of chromosome 11 and 6. 14q+ markers are frequent in patients at advanced stage, but are almost always within complex abnormalities. The number of clonal abnormalities in the CLL cells has a strong prognostic impact. Trisomy 12 as a single abnormality is an adverse prognostic sign, whereas patients with 13q abnormalities generally do comparatively well. Lymphoid leukaemia with monoclonal immunoglobulin secretion frequently involves clonal chromosomal abnormalities, and the type of change is similar to that seen in true CLL. In B cell prolymphocytic leukaemia, t(11;14) is a common finding, together with trisomy 12. T cell prolymphocytic leukaemia is characterized by an inversion of the long arm of chromosome 14, with breaks at q11 and q32, and trisomy of 8q, whereas large granular lymphocytic leukaemia has shown no consistent abnormality. Hairy cell leukaemia seems to involve a specific set of non-random chromosome abnormalities, such as inv(5)9.

Complex karyotypic evolution in B-cell chronic lymphocytic leukemia

Cytogenetic analysis at diagnosis in a female patient with chronic B-cell leukemia showed a single abnormal clone with a 4p+ abnormality, 46,XX, -4, +der(4)t(4;?)(p16;?). Six additional clones evolved from this clone during the following 4 1/2 years and showed 3p+, 4p-, and 11q- chromosomes in addition to the 4p+ abnormality. Immunoglobulin heavy chain gene rearrangement studies showed two rearranged bands and a faint germline band. Following splenectomy, a strong germline and faint rearranged bands were seen, suggesting that the majority of cells were normal, whereas cytogenetic studies showed that the karyotypically abnormal cells were still present. The combination of cytogenetic and Ig gene rearrangement studies provides detailed information regarding the number of circulating normal and leukemic cells.

Aberrations of chromosome 6 in 193 newly diagnosed untreated cases of chronic lymphocytic leukemia

Aberrations of chromosome 6 were observed in 11 of 193 cases of chronic lymphocytic leukemia diagnosed January 1, 1984-November 1, 1988 and investigated cytogenetically within 30 days after diagnosis. The 6p was rearranged in 5 cases: 4 balanced and 1 unbalanced translocation. The 6q was involved in 6 cases: 4 deletions and 2 balanced translocations. Three of the del(6q) may be identical: del(6)(q13q27). In two cases there were no additional aberrations. Aberrations of chromosome 6 correlated significantly with an advanced clinical stage, diffuse pattern of bone marrow infiltration, and increased SmIgM-fluorescence intensity. All these factors are associated with poor prognosis. Although the number of cases with 6q aberrations is still too small and the observation period too short to show significant influence on survival, the presence of 6q aberrations at diagnosis may prove useful in delineating a subtype of chronic lymphocytic leukemia with poor prognosis.

Karyotypic evolution in B-cell chronic lymphocytic leukaemia

Sequential cytogenetic studies were performed on a minimum of two and a maximum of nine occasions (mean 3.6) on the peripheral blood leucocytes of 112 patients with B-CLL. On initial cytogenetic analysis, 58 had a normal karyotype and 64 had a clonal abnormality. Karyotypic evolution occurred in 18 patients (16%). There was no significant difference in the incidence of disease progression between patients with a stable karyotype and those who underwent karyotypic evolution. In only one patient was there a clear association between disease progression, a change in cell morphology and karyotypic evolution.

Clonal chromosomal changes in chronic lymphocytic leukemia

Cytogenetic analysis was carried out in 28 B-CLL patients (21 males and 7 females, 38-85 years old, with median age 64 years, disease stage O-IV). Peripheral nominator cells (1 x 10(7)) or isolated B-lymphocytes were incubated in vitro for 5-7 days. The cells were stimulated by pokeweed mitogen (PWM), or phorbol myristate-acetate (PMA), with or without 10% conditioned medium (CM) derived from a T cell leukemia line or 10% B-cell growth factor (BCGF). Twenty-two patients (79%) responded to PWM + CM; 5 out of 5 patients responded to PWM + BCGF. The average mitotic index (+/- S.E.M.) for PWM, PMA, PWM + CM, PMA + CM, PWM + BCGF were 0.13 +/- 0.01, 0.24 +/- 0.13, 0.51 +/- 0.11, 0.14 +/- 0.06 and 0.63 +/- 0.15, respectively. Cytogenetic analysis revealed the presence of abnormal karyotypes in 22 patients. Fourteen patients (50%) had clonal chromosome aberrations which included: monosomy 1, 9, 17, 18, 21, and X chromosome, and trisomy of chromosomes 7, 9, 20, 21 and 22. The clonal structural aberrations were i(6q), inv(12) (q15q24), del(5) (p13p15), del(10) (q24). No homogeneously staining regions (HSR) were observed. Four patients with resistance to anti-neoplastic drugs showed the presence of double minute chromosomes (dmin) ranging in frequency from 5 to 50%.

Establishment of a karyotypically normal B-chronic lymphocytic leukemia cell line; evidence of leukemic origin by immunoglobulin gene rearrangement

A new Epstein-Barr virus (EBV) transformed cell line was established from a patient with B-chronic lymphocytic leukemia (B-CLL). The karyotype of the cell line has remained normal for over 12 months in culture; however, identical heavy and light chain immunoglobulin (Ig) gene rearrangements in the patient's blood and the cell line provided evidence that the EBV transformed cells were derived from the neoplastic clone.

Cytogenetic and molecular changes in chronic B-cell leukemia

Cytogenetic studies using B-cell mitogens indicate that approximately 50% of patients with chronic B-cell leukemia (CLL) have chromosome abnormalities. The most common abnormality is an additional chromosome 12, either as the sole abnormality or in conjunction with other abnormalities such as 14q+, 6q-, and 11q-. In two instances, the 14q+ is a result of a translocation from either chromosome 11, t(11;14), or chromosome 19, t(14;19). These two translocations led to the identification of the bcl-1 and bcl-3 genes located on chromosomes 11 and 19, respectively. Very few instances of oncogene activation have been described and it does not seem to be an important mechanism in the pathogenesis of CLL. Further cytogenetic and molecular studies may provide clues for the identification of the genes involved in CLL.

Primary chromosome abnormalities in human neoplasia

At the cellular level, cancer is a genetic disease; genetic changes in somatic cells are essential events in neoplasia. In a majority of cases these changes involve large enough blocks of genetic material to be visible in the microscope. The chromosome aberrations in neoplastic disorders are probably of three kinds: (1) primary abnormalities, which are essential steps in establishing the tumor; (2) secondary abnormalities, which develop only after the tumor has developed, but which nevertheless may be important in tumor progression; and (3) cytogenetic noise, which is the background level of nonconsequential aberrations. These latter changes are, in contrast to the primary and secondary changes, randomly distributed throughout the genome. The primary abnormalities, of which several dozens have now been identified, are mostly strictly correlated with particular diseases and even with histopathological subtypes within a given disease. This has been evident in the leukemias for some years already, and information now accumulating on solid tumor karyology indicates a similar situation. Clonal chromosome abnormalities are a feature of both benign and malignant neoplasms, although the changes are often less massive in the former. Apart from being clinically useful as a diagnostic technique and an aid in prognostication, tumor cytogenetics also plays a role in identifying those genomic sites which harbor genes essential in the pathogenesis of neoplastic lesions. So far, two functionally different classes of directly cancer-relevant genes have been detected, the oncogenes and antioncogenes. There is every reason to believe that future investigations with cytogenetic and recombinant DNA methods will add to our knowledge of the biology of human neoplasia, in those tumor types where the characteristic genetic change is already partially known, and by identifying hitherto unknown karyotypic abnormalities.

Cytogenetic study of chronic lymphocytic leukemia in ten Japanese patients with a case of the same chromosome abnormality both in T and B cells

Peripheral blood lymphocytes from ten patients with chronic lymphocytic leukemia (CLL) stimulated with phytohemagglutinin (PHA), pokeweed mitogen (PWM), Epstein-Barr virus (EBV), and T-cell growth factor were studied cytogenetically. Eight of ten cases were clinically and immunologically B-cell CLL, and two cases were T-cell CLL. Chromosome analysis revealed that one patient, diagnosed as B-cell CLL, had a clonal abnormality in the leukemic cells. The abnormal karyotype was 46,XY,+3,-15,t(10;19)(q22;p13),t(11;14) (q13;q32),13q+,17q-. The frequencies of the abnormal cell stimulated with PHA, PWM, and EBV were 50%, 13%, and 100%, respectively. Finding the same clonal abnormality after stimulation with three different mitogens suggests that the factor responsible for the development of CLL might affect the stem cell common to T-cell and B-cell lymphocytes. In cells with this abnormal karyotype, chromosome 13q+ seems to have a homogeneous staining region. In the present series of B-cell CLL, no trisomy 12 known to be the specific chromosome abnormality was observed.

Consistency of chromosomal aberrations in chronic B-lymphocytic leukemia. A longitudinal cytogenetic study of 41 patients

Serial chromosome analyses with a mean of 3.7 samplings during a mean interval of 4.2 years (range, 1.5 to 8.6 years) were performed on B-cell mitogen-activated chronic B-lymphocytic leukemia (CLL) cells from 41 patients. Twenty-four of these patients (59%) had progressive disease. Clonal chromosomal aberrations were found in 28 patients; 12 had an extra chromosome 12. Thirty patients (73%), 17 with and 13 without clonal aberrations, retained their karyotype throughout the study, although six lost minor subclones. In five patients (12%), a clonal aberration was found only once. Six patients (15%) showed changes of the karyotype. One treated patient with multiple aberrations acquired another monosomy. Another patient with multiple aberrations and prolymphocytic transformation gained a marker chromosome. One treated patient with an initially normal karyotype acquired two independent clonal aberrations. Three patients lost one subclone but retained another clone that increased in frequency. In two cases, clonal changes were associated with clinical changes. The chromosomal aberrations are mostly established already at diagnosis and mark the disease of the CLL patient. Cytogenetic analysis at any time is representative and useful in the prognosis prediction.

Chromosomal aberrations in progressive and indolent chronic B-lymphocytic leukaemia. A longitudinal study

Chromosome analyses of B-cell mitogen-activated cells from 95 patients with chronic B-lymphocytic leukaemia revealed clonal chromosomal aberrations in 50 patients (53%), of which 24 had an extra chromosome 12 with or without other aberrations. Patients with clonal aberrations, especially those with +12, had poorer survival than other patients. Longitudinal studies, with a mean of 3.5 samplings during a median interval of 3.5 years, were performed in 41 patients, of which 24 (59%) had progressive disease. Twenty-nine of the patients in the longitudinal study (71%), 16 with and 13 without clonal aberrations, retained their karyotype unaltered. In 6 patients a clonal aberration was found only once. Six patients showed minor changes of the karyotype. The karyotype seems to be established at diagnosis, and marks the disease of the individual CLL-patient.