Report of 34 patients with clonal chromosomal abnormalities in Philadelphia-negative cells during imatinib treatment of Philadelphia-positive chronic myeloid leukemia

Chronic myelogenous leukemia, BCR-ABL1+

Session 1 of the 2007 Workshop of the Society for Hematopathology/European Association for Haematopathology focused on chronic myelogenous leukemia, BCR-ABL1+ (CML). CML is a myeloproliferative neoplasm arising at the level of a pluripotent stem cell and consistently associated with the BCR-ABL1 fusion gene. CML most commonly manifests in a chronic phase of the disease with neutrophilic leukocytosis, and the demonstration of the Philadelphia chromosome is the ultimate confirmation of the diagnosis. However, in select cases, the initial diagnosis remains challenging, and a number of issues pertaining to the manifestations and disease evolution remain unresolved. These issues have been illustrated by the cases submitted to our workshop and include unusual manifestations of CML, including manifestation in the accelerated and/or blast phase, and patterns of disease progression and therapy resistance in the era of protein tyrosine kinase inhibitor therapy.

t(5;6;12) associated with resistance to imatinib mesylate in chronic myeloid leukemia

A patient with t(9;22)-positive chronic myelogenous leukemia (CML) developed a resistance to therapy with imatinib mesylate (Glivec) which coincided with the appearance of t(5;6;12) in the same cells with t(9;22) [46,XX,t(5;6;12)(q14?;q21?;q23?),t(9;22)(q34;q11)]. She remains in a continuous chronic phase of CML. This is the first reported instance of karyotype evolution temporally associated, and possibly involved, with the induction of resistance to imatinib mesylate but without any signs of evolution of leukemia toward a more anaplastic and aggressive form.

Management of the advanced phases of chronic myelogenous leukemia in the era of tyrosine kinase inhibitors

Imatinib has revolutionised the management of chronic phase chronic myelogenous leukemia (CML). Unfortunately it has had less of an impact on the management of the advanced phases of CML. These historically difficult-to-treat phases of disease remain largely resistant to therapy. Even when responses are obtained with the tyrosine kinase inhibitors, they are brief, particularly in blast phase (BP) disease. Allogeneic stem cell transplantation is the only curative option for these patients and should be considered early as an integral part of the treatment plan. But transplant outcomes are dependent on cytogenetic and gross disease burden at the time of transplant. This review will compare and contrast the various tyrosine kinase- and non-tyrosine kinase inhibitor-based treatments for accelerated and BP CML before allogeneic transplantation.

A myeloproliferative disorder may hide another one

Chronic myeloproliferative disorders (MPDs) are divided into Philadelphia-positive chronic myeloid leukemia (CML) and Philadelphia-negative disorders including polycythemia vera, essential thrombocythemia and idiopathic myelofibrosis (IMF). Concomitance of a CML and another MPD is a rare event. We report here the case of a patient presenting initially with IMF who developed a Philadelphia-positive CML 7 years later. At the time of CML diagnosis, two distinct clones were present, one with a 13q deletion and one with a t(9;22). We raise the problem of a CML developing on an initial IMF, or two MPDs occurring from a common or two different stem cells.

Targeted treatment of chronic myeloid leukemia: role of imatinib

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by clonal expansion of pleuripotent hematopoetic stem cells. The incidence of CML is 1 to 2 cases per 100,000 people per year; in the Western Hemisphere, CML accounts for 15% of leukemias in adults. Discovery of the specific karyotypic abnormality of the Philadelphia (Ph) chromosome in the pathogenesis of CML has led to a better understanding of the disease and hence to an advancement of targeted therapeutics. Availability of imatinib as an accepted targeted therapy in newly diagnosed patients has changed the treatment paradigm in CML. The majority of CML patients in chronic phase achieve excellent and durable responses with standard-dose imatinib. Mechanisms of primary and secondary resistance to imatinib in CML have been extensively studied and newer tyrosine kinase inhibitors are now being evaluated for clinical use. It is important that at any time the CML treatment and response remain optimal and thus patients on imatinib require continuous monitoring for early detection of resistance. This review will discuss the treatment and guidelines for monitoring CML patients in the imatinib era.

Transient trisomy 8 abnormality in Philadelphia-negative cells during imatinib mesylate treatment of chronic myelogenous leukemia

We investigated chronic myelogenous leukemia (CML) patients who developed trisomy 8 abnormalities in Philadelphia-negative (Ph-) cells during imatinib mesylate treatment to evaluate the clinical outcome and laboratory features. Of the 470 CML patients, 1.5% (n = 7) developed trisomy 8 chromosomal abnormalities in Ph- cells. The median interval of the first trisomy 8 observation was 12 months. Our follow-up cytogenetic evaluations revealed that six of the patients demonstrated a complete or partial cytogenetic response and that all of the six patients revealed no dysplastic changes following a bone marrow examination. Moreover, the percentage of trisomy 8 in metaphase karyotyping has decreased in five of the seven subjects. In conclusion, these results suggest that the emergence of trisomy 8 in Ph- cells is transient and not related to therapy-related myelodysplasia or acute leukemia.

Chronic myeloid leukaemia: the evolution of gene-targeted therapy

Chronic myeloid leukaemia (CML) was the first human cancer linked to an acquired chromosomal abnormality, subsequently shown to be a reciprocal translocation between chromosomes 9 and 22. The resulting fusion gene product, BCR-ABL, was shown to be the causative agent of the disease. CML has an incidence of around 1-2 cases per 100,000; in Australia, there are probably more than 200 new cases per year and more than 1300 prevalent cases. Treatment of CML with imatinib has been a powerful vindication of the concept of rational, gene-targeted drug design. Five-year published experience with imatinib at 400 mg orally daily demonstrates 89% overall survival and an estimated 93% freedom from disease progression. Adverse effects are mostly mild and transient. Higher doses of imatinib may be more efficacious and will be studied in upcoming clinical trials in Australia; however, imatinib is almost certainly not curative. Up to 28% of patients may have to stop imatinib because of intolerance or disease resistance, mostly due to point mutations of BCR-ABL. In this situation, many patients will respond to second- and third-generation tyrosine kinase inhibitors. Management of CML patients should involve close monitoring, especially in the first 2 years, with regular cytogenetics and quantitative polymerase chain reaction to optimise response and identify suboptimal responders as early as possible. Bone marrow transplantation remains the only known cure, but is reserved for patients whose kinase inhibitor therapy has failed, or who have advanced disease (accelerated phase or blastic transformation).

Emerging stem cell concepts for imatinib-resistant chronic myeloid leukaemia: implications for the biology, management, and therapy of the disease

Chronic myeloid leukaemia (CML) is a myeloid neoplasm defined by the BCR/ABL oncoprotein that is considered essential for leukaemogenesis and accumulation of neoplastic cells. The BCR/ABL kinase inhibitor imatinib is an effective agent in most patients and can now be regarded as front-line therapy. Hence, intrinsic and acquired resistance to imatinib has been described and is an emerging challenge in clinical practice. While CML stem cells display primary resistance, stem cell subclones may, in addition, acquire imatinib-resistant mutants of BCR/ABL. Other factors that are considered to contribute to stem cell resistance include the genetic background, clonal evolution, additional biological features of subclones, gene amplifications, silencing of tumour suppressor genes and specific pharmacological aspects. In this article, mechanisms of resistance of CML (stem) cells against imatinib and other BCR/ABL inhibitors are discussed, together with strategies to overcome and/or to prevent resistance with available drugs or novel anti-leukaemic approaches.

Secondary myelodysplastic syndrome in a patient with Philadelphia-positive acute lymphoblastic leukemia after achieving a major molecular response with hyperCVAD plus imatinib mesylate

The addition of imatinib to high-intensity chemotherapy has improved the outcome of patients with Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL). However, the possible long-term side effects of this combination are not yet known. Development of new clonal abnormalities in complete cytogenetic remission after treatment with imatinib has been reported in patients with chronic myeloid leukemia but not in patients with Ph-positive ALL. Here, we present a patient with Ph-positive ALL who received hyperCVAD plus imatinib and achieved hematologic, cytogenetic, and major molecular responses. The patient then developed myelodysplastic syndrome and solitary central nervous system relapse of ALL.

Successful application of a direct detection slide-based sequential phenotype/genotype assay using archived bone marrow smears and paraffin embedded tissue sections

Identification of genetic abnormalities in pathological samples is critical for accurate diagnosis, risk stratification, detection of minimal residual disease, and assessment of response to therapy. Interphase fluorescence in situ hybridization analysis is the standard cytogenetic assay used by many laboratories to detect specific clonal karyotypic aberrations in formalin-fixed, paraffin-embedded tissue. However, direct correlation with immunophenotype or morphology in individual cells is rarely performed because the procedural steps are labor intensive and usually require extensive troubleshooting. In this study, we present a sequential fluorescence in situ hybridization-based technique that uses the identical archived bone marrow smears or paraffin-embedded tissue sections previously evaluated by a pathologist for morphological or immunohistochemical characteristics. This approach is relatively straightforward, using uncomplicated pretreatment and hybridization conditions and basic equipment attached to an automated image analyzer with image capture software to record the location of targeted cells for genotypic/phenotype correlation. Furthermore, the method has proved reliable and reproducible on test samples regardless of specimen age, tissue type, or referring institution.

The prognosis for patients with chronic myeloid leukemia who have clonal cytogenetic abnormalities in philadelphia chromosome-negative cells

BACKGROUND

Clonal cytogenetic abnormalities (CCA) were detected in Philadelphia chromosome (Ph)-negative cells in some patients with chronic myeloid leukemia (CML) who attained a cytogenetic response to imatinib mesylate. In some patients, CCA/Ph-negative status was associated with myelodysplasia or acute myeloid leukemia. The objective of the current study was to determine the prognostic impact of CCA/Ph-negative cells.

METHODS

The authors compared the pretherapeutic risk factors (Kruskall-Wallis test), exposure to cytotoxic drugs (chi-square test), and overall and progression-free survival (Kaplan-Meyer and logistic regression analysis, respectively) of 515 patients with mostly chronic-phase CML who were treated with imatinib mesylate after failure of interferon-alpha according to whether they attained a major cytogenetic response (MCR) (n = 324 patients), an MCR with CCA/Ph-negative status (n = 30 patients), or no MCR (n = 161 patients).

RESULTS

CCA/Ph-negative status most frequently involved chromosomes Y, 8, and 7. No significant differences in pretherapeutic risk factors were detected between patients who attained an MCR with and without CCA/Ph-negative cells, except that exposure to alkylating agents was more frequent in patients with CCA/Ph-negative cells, and overall and progression-free survival were identical. With a median follow-up of 51 months, only 2 patients developed myelodysplastic syndromes (MDS).

CONCLUSIONS

The overall prognosis for patients who had CML with CCA/Ph-negative status was good and was driven by the CML response to imatinib mesylate. Isolated CCA/Ph-negative cells in the absence of morphologic evidence of MDS do not justify a change in therapy.

Monosomy 7 with severe myelodysplasia developing during imatinib treatment of Philadelphia-positive chronic myeloid leukemia: two cases with a different outcome

Chromosomal abnormalities in Ph-negative metaphases from patients with chronic myeloid leukemia (CML) treated with imatinib have been described in some cases. Trisomy 8 is the most frequent, but monosomy 7 has also been described. However, the association of these chromosomal alterations with myelodysplasia has been scarcely reported. We report the appearance of monosomy 7 in Ph-negative cells, associated with severe dysplasia, in two patients with CML treated with imatinib, with a different outcome: one with a transient evolution and the other evolving to acute myeloid leukemia.

Recent advances in the understanding of mastocytosis: the role of KIT mutations

Mastocytosis is a heterogeneous disorder characterised by the expansion and accumulation of mast cells in different organs and tissues. Mast cell physiology is closely dependent on activation of the stem cell factor/Kit signalling pathways and accumulating evidences confirm the physiopathological key role of activating KIT mutations (typically D816V) in mastocytosis and their relationship with the clinical manifestations of the disease. This paper reviews the most recent advances in the understanding of the molecular mechanisms associated with KIT mutations in mastocytosis, including recent data about the use of new therapies targeting the Kit molecule and its associated downstream signalling pathways.

Chromosomal abnormalities in Philadelphia chromosome negative metaphases appearing during imatinib mesylate therapy in patients with newly diagnosed chronic myeloid leukemia in chronic phase

The development of chromosomal abnormalities (CAs) in the Philadelphia chromosome (Ph)-negative metaphases during imatinib (IM) therapy in patients with newly diagnosed chronic myecloid leukemia (CML) has been reported only anecdotally. We assessed the frequency and significance of this phenomenon among 258 patients with newly diagnosed CML in chronic phase receiving IM. After a median follow-up of 37 months, 21 (9%) patients developed 23 CAs in Ph-negative cells; excluding -Y, this incidence was 5%. Sixteen (70%) of all CAs were observed in 2 or more metaphases. The median time from start of IM to the appearance of CAs was 18 months. The most common CAs were -Y and + 8 in 9 and 3 patients, respectively. CAs were less frequent in young patients (P = .02) and those treated with high-dose IM (P = .03). In all but 3 patients, CAs were transient and disappeared after a median of 5 months. One patient developed acute myeloid leukemia (associated with - 7). At last follow-up, 3 patients died from transplantation-related complications, myocardial infarction, and progressive disease and 2 lost cytogenetic response. CAs occur in Ph-negative cells in a small percentage of patients with newly diagnosed CML treated with IM. In rare instances, these could reflect the emergence of a new malignant clone.

Characterization of Ph-negative abnormal clones emerging during imatinib therapy

BACKGROUND

Imatinib is a tyrosine kinase-specific inhibitor widely used for the treatment of chronic myeloid leukemia (CML). Studies reported the occurrence of additional cytogenetic abnormalities in the Philadelphia chromosome (Ph)-negative cell population emerging after treatment-induced suppression of the Ph-positive clone. These abnormalities were described in a relatively high proportion of patients treated with imatinib compared with the anecdotal reports of similar cases in patients treated with other drugs. However, the origin of these abnormalities as well as their biological and clinical significance are unknown.

METHODS

The study involved 13 cases of patients diagnosed with CML carrying cytogenetic abnormalities in their Ph-negative cell population after imatinib treatment. The presence of the markers within the CD34+ stem cell compartment and the cell culture growth were analyzed and patients were followed over time.

RESULTS

CD34+ cells express the cytogenetic markers present in Ph- cells, suggesting a possible involvement of the stem cell population. Cultured cells showed normal growth in all but 1 patient. No growth advantage was demonstrated for the Ph-negative or the Ph-positive clone after cell culture.

CONCLUSIONS

After follow-up of up to 49 months, none of the patients had evolved to myelodysplasia or acute leukemia. Hypothesis regarding the biological and clinical significance of these abnormalities are formulated.

Acute myeloid leukemia developing during imatinib mesylate therapy for chronic myeloid leukemia in the absence of new cytogenetic abnormalities

The BCR/ABL tyrosine kinase inhibitor imatinib mesylate produces a high rate of cytogenetic responses in patients with Philadelphia (Ph)-positive chronic myeloid leukemia (CML), but secondary clonal chromosome abnormalities may develop in Ph-negative cells, and acute myeloid leukemia (AML) has been reported in patients with secondary chromosome abnormalities. We report a patient who developed AML during imatinib treatment of Ph-positive CML despite a cytogenetic response and absence of secondary chromosome abnormalities. Thus, development of AML as a rare event in CML patients with cytogenetic responses to imatinib therapy does not depend on the development of secondary cytogenetic abnormalities.

Trisomy 8 as the sole chromosomal aberration in acute myeloid leukemia and myelodysplastic syndromes

Trisomy 8 as the sole abnormality is the most common karyotypic finding in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), occurring in approximately 5% and 10% of the cytogenetically abnormal cases, respectively. However, despite the high frequency of +8, much remains to be elucidated as regards its epidemiology, etiology, clinical impact, association with other chromosomal abnormalities, cell of origin, and functional and pathogenetic consequences. Here, we summarize and review these various aspects of trisomy 8, focusing on AMLs and MDS harboring this abnormality as a single change.

Cytogenetic evolution patterns in CML post-SCT

The cytogenetic evolution patterns in chronic myeloid leukemia (CML) after allogeneic (allo) stem cell transplantation (SCT) are different from the ones observed in non-transplanted patients, a phenomenon suggested to be caused by the conditioning regime. We reviewed 131 CMLs displaying karyotypic evolution after SCT (122 allo, nine autologous (auto)), treated at Lund University Hospital or reported in the literature. Major route abnormalities (i.e., +8, +Ph, i(17q), +19, +21, +17 and -7) were seen in 14%, balanced aberrations in 61%, hyperdiploidy in 19%, pseudodiploidy in 79%, divergent clones in 14%, and Ph-negative clones in 21%. The breakpoints involved in secondary structural rearrangements clustered at 1q21, 1q32, 7q22, 9q34, 11q13, 11q23, 12q24, 13q14, 17q10 and 22q11. Cytogenetic abnormalities common in AML after genotoxic exposure, that is, der(1;7)(q10;p10), del(3p), -5, del(5q), -7, -17, der(17p), -18, and -21, were only rarely seen post-SCT. Comparing the cytogenetic features in relation to type of SCT revealed that balanced aberrations were significantly more common after allo than after auto SCT (64 and 22%, respectively, P=0.03). In addition, there was a trend as regards hyperdiploidy being more common after auto (P=0.07) and pseudodiploidy being more frequent after allo SCT (P=0.09). Possible reasons for these differences are discussed.

Philadelphia-negative clonal hematopoiesis following imatinib therapy in patients with chronic myeloid leukemia: a report of nine cases and analysis of predictive factors

There are increasing reports of Philadelphia-negative (Ph-negative) clonal hematopoiesis developing among patients with chronic myeloid leukemia (CML) treated with imatinib mesylate (IM). To establish the incidence and significance of these chromosomal abnormalities, we analyzed data on 141 consecutive patients with CML treated with IM at the British Columbia Cancer Agency and Vancouver General Hospital from 1999 to 2004. The cumulative incidence of developing a Ph-negative clone three years from the start of IM was 8.7% at a median of 13.3 months. The Ph-negative clonal abnormalities included monosomy 7 and/or trisomy 8 (seven patients), monosomy for chromosomes X and 22 (one patient), and a (12;16) translocation (one patient). Two of the patients presented with the same chromosomal abnormality in both Ph-negative and Ph-positive cells. None of the Ph-negative clonal abnormalities was associated with myelodysplasia. In a multivariate analysis, an interval from diagnosis to initiation of IM of 1 year or less was associated with an increased risk of developing a Ph-negative clone (relative risk = 20.2; P = 0.025). There was no difference, however, in event-free survival between patients who did and did not develop Ph-negative clones. Therefore, while the development of Ph-negative clonal hematopoiesis in patients with CML treated with IM is uncommon, it appears to be more frequent than that previously seen with IFN, but it does not seem to confer a worse prognosis.

Imatinib-associated neutropenia may not be overcome by filgrastim treatment in patients with blastic phase of chronic myeloid leukaemia

Imatinib mesylate is a very effective treatment in patients with Philadelphia (Ph)-positive chronic myeloid leukaemia (CML). However, in patients with advanced phase CML, it is still unclear whether, in the presence of myelosuppression, therapy with imatinib should be continued. It has been reported that intermittent filgrastim treatment may overcome imatinib-associated neutropenia and allow improved delivery of imatinib. Such combined sequential treatment is theoretically attractive as it may lead to better disease response. Here, we report a patient with blastic phase CML who developed severe and prolonged myelosuppression during imatinib treatment. Despite cessation of imatinib and 2 months of filgrastim therapy neither recurrence of Ph-positive or Ph-negative cells occurred. We conclude that filgrastim treatment may not always reverse imatinib-associated neutropenia therefore the decision of continued imatinib therapy in patients with advanced CML should be taken with caution.

Random aneuploidy in CML patients at diagnosis and under imatinib treatment

Chronic myeloid leukemia (CML) is characterized by the presence of a BCR-ABL fusion gene, which is the result of a reciprocal translocation between chromosomes 9 and 22, and is cytogenetically visible as a shortened chromosome 22 (Philadelphia). Research during the past two decades has established that BCR-ABL is probably the pathogenetic pathway leading to CML, and that constitutive tyrosine kinase activity is central to BCR-ABL capacity to transform hematopoietic cells in vitro and in vivo. The tyrosine kinase inhibitor imatinib mesylate was introduced into the treatment regimen for CML in 1998. During the last few years, reports on chromosomal changes during imatinib treatment have been described. In this study, we evaluated the random aneuploidy rate with chromosomes 9 and 18 in bone marrow from treated and untreated patients. We found higher aneuploidy rates in both treated and untreated patients compared to the control group. In three patients who were treated with imatinib mesylate for more than 1.5 years, triploidy also appeared in some nuclei. To our knowledge, this is the first report on new chromosomal changes such as random aneuploidy and triploidy under imatinib treatment, but more studies are needed to investigate the long-term effect of the imatinib treatment on genetic instability.

Myelodysplastic syndromes and acute leukemia developing after imatinib mesylate therapy for chronic myeloid leukemia

During therapy with imatinib, some patients with chronic myeloid leukemia (CML) develop chromosomal abnormalities in Philadelphia chromosome (Ph)-negative cells. These abnormalities are frequently transient and their clinical consequence is unclear. Although some reports have suggested that the abnormalities might be associated with secondary myelodysplastic syndrome (MDS), the diagnosis has not always been established using standard criteria. We report 3 cases of patients treated with imatinib for CML who were subsequently found to have chromosomal abnormalities in Ph-negative cells. One of them developed acute myelogenous leukemia (AML) and the other 2 developed high-risk MDS that rapidly transformed to AML. These cases were identified in a total study group of 1701 patients. Although these occurrences are rare, the findings highlight the need for close monitoring of patients with CML treated with imatinib.

Limited clinical value of regular bone marrow cytogenetic analysis in imatinib-treated chronic phase CML patients monitored by RQ-PCR for BCR-ABL

Real-time quantitative polymerase chain reaction (PCR) for BCR-ABL mRNA in the peripheral blood (RQ-PCR) provides an accurate and reliable measure of response to therapy in chronic myeloid leukaemia (CML). We wanted to determine in what circumstances additional clinically relevant information was provided by simultaneous cytogenetic analysis in RQ-PCR monitored patients receiving imatinib treatment. We analysed 828 simultaneous RQ-PCR and bone marrow cytogenetic analyses from 183 patients with chronic phase CML with a median follow-up of 20 months. Cytogenetic progression was defined as Philadelphia (Ph)-positive clonal evolution, loss of complete cytogenetic response or an increase of > or = 20% Ph-positive cells. Cytogenetic progression occurred in 24/183 (13%) patients. At the time of cytogenetic progression, none of the 24 patients had a major molecular response (MMR; > or = 3-log reduction in BCR-ABL from standardised baseline). There were 320 RQ-PCR results from 95 patients indicating MMR. No abnormality was detected in any of the corresponding cytogenetic analyses. A policy of regular RQ-PCR monitoring with cytogenetic analysis targetted only to patients who have not achieved, or have lost MMR would represent a rational approach to monitoring and spare most patients the discomfort of multiple marrow aspirates. This approach depends upon availability of an accurate, reproducible RQ-PCR assay with ongoing quality assurance.

[Hematological side effects of tyrosine kinase inhibition using imatinib]

Imatinib (STI571, Gleevec/Glivec) and other small-molecule tyrosine kinase inhibitors are highly effective in the treatment of chronic myeloid leukemia (CML), gastrointestinal stromal tumors and, for example, eosinophilia-associated chronic myeloproliferative disorders. This molecularly targeted approach disrupts abnormal tyrosine kinase dependent signalling pathways, thus providing a preferred treatment option for selected neoplastic disorders with activating mutations of Abelson-, Abl-related-, Kit-, and platelet-derived growth factor receptor A and B genes. Loss of response to imatinib may be due to an acquired resistance of emerging mutant tumor cell clones. Therapy is generally well tolerated. However, toxicities including edema, skin rashes, fatigue, nausea and myelosuppression have been reported. Philadelphia/Bcr-Abl-negative clonal chromosomal abnormalities may develop. Bone marrow trephines obtained from CML patients in complete remission with prolonged pancytopenia secondary to imatinib generally show marrow hypoplasia. Morphological features may be in keeping with either aplastic anemia or myelodysplasia developing in Philadelphia-negative hematopoiesis. Single or multilineage myelodysplasia may be accompanied by an excess of blasts and rarely evolves into acute leukemia in CML patients. Severe adverse hematological effects of imatinib are extremely rare. Current questions involve the molecular mechanisms of hematological side effects of tyrosine kinase inhibitors with special regard to the emergence of distinct aberrant clones.

Induction of centrosome and chromosome aberrations by imatinib in vitro

Imatinib (STI571, Gleevec/Glivec) is a potent selective tyrosine kinase inhibitor and is used successfully in the treatment of chronic myeloid leukemia (CML). While karyotype alterations, in addition to the Philadelphia chromosome, are a common phenomenon of progressing CML, the observation of BCR-ABL-negative leukemic clones with distinct aberrant karyotypes under an imatinib regimen is not yet understood. Here we test the hypothesis that such tumor clones may be induced de novo from normal cells by imatinib. In vitro experiments with varying drug concentrations (5-20 microM) were performed on normal human dermal fibroblasts (NHDF), Chinese hamster embryonal and Indian muntjak fibroblasts. After 3 weeks of treatment, analysis of cell cultures by centrosome immunostaining and conventional cytogenetics revealed that imatinib induced centrosome and chromosome aberrations in all cultures in a significant dose-dependent and species-independent manner. Moreover, the results of NHDF long-term culture experiments demonstrated that aberrant phenotypes, emerging under imatinib treatment for 12 weeks, were not reversible after prolonged propagation omitting the drug. These observations suggest a causative role of imatinib in the origin of centrosome and karyotype aberrations (genetic instability) and thus may explain the emergence of clonal chromosomal abnormalities in BCR-ABL-negative progenitor cells under imatinib therapy.

Durable molecular remissions with a single cycle of timed sequential consolidation chemotherapy in acute promyelocytic leukemia

In a pilot study to reduce the duration of treatment and potential long-term toxicities, 39 patients with acute promyelocytic leukemia in remission received a single cycle of intensive consolidation therapy, followed by intermittent ATRA maintenance. Consolidation therapy required prolonged hospitalization and was associated with a high incidence of mucositis (43% grade II or greater) and documented infection (45%). No deaths occurred during consolidation. Seven patients have relapsed; all other patients are in molecular remission (median follow-up, 2.75 years). Kaplan-Meier estimate of 3 year disease-free survival is 73% (95% confidence interval 55-91%). The relapse rate (0.06 relapses/patient-year of follow-up) is well within the range of larger published series that administer more prolonged consolidation. One patient has developed secondary myelodysplastic syndrome. These pilot data suggest that decreasing the total duration of consolidation chemotherapy did not compromise disease-free survival for APL patients induced with ATRA/anthracycline and given intermittent ATRA maintenance. However, the toxicity of the consolidation module and the development of secondary myelodysplasia despite decreased total therapy emphasize the need to further improve and refine curative therapy for APL.

Monitoring minimal residual disease in BCR-ABL-positive chronic myeloid leukemia in the imatinib era

PURPOSE OF REVIEW

The total number of leukemia cells in the body is reduced very substantially in patients with BCR-ABL-positive chronic myeloid leukemia (CML) responding to imatinib. This reduction is seen first as restoration of Ph negativity in blood and marrow and thereafter as decreasing BCR-ABL transcript levels assayed by quantitative polymerase chain reaction (PCR). Most patients with newly diagnosed chronic-phase CML who receive imatinib achieve complete cytogenetic remission (CCYR) and low levels of BCR-ABL transcripts, a status that seems to predict for relatively long survival compared with previous treatments.

RECENT FINDINGS

Patients treated with 400 mg daily who achieved a reduction in BCR-ABL transcript numbers equal or greater than 3 logs compared with a baseline value have a significantly better progression-free survival than those who achieved lesser degrees of response. The presence of Ph-positive subclones with point mutations in the ABL kinase domain correlates with "acquired" resistance to imatinib and some mutations are associated with greater resistance than others. Preliminary evidence suggests that P-loop mutations are especially likely to be associated with progression to advanced-phase disease.

SUMMARY

Patients with CML should be monitored routinely by serial cytogenetic analysis of bone marrow until Ph negativity is achieved. Thereafter serial quantitative-PCR studies should be undertaken at approximately 3-month intervals and probably also bone marrow cytogenetic studies at longer intervals. Routine studies for ABL kinase domain mutations may also be advisable. The observation of increasing quantities of residual leukemia or expansion of a mutated clone suggests the need to modify therapy.