Chromothripsis - Extensive Chromosomal Rearrangements and Their Significance in Cancer.

BACKGROUND: Chromosome rearrangements play an important role in cancer pathophysiology. Recently, chromothripsis has been proposed among the mechanisms leading to their formation. Chromothripsis leads to fragmentation of chromosomes and their reconstitution with tens to hundreds of rearrangements clustered in small genome regions. In contrast to the traditional concept of malignant transformation, abnormalities caused by chromothripsis are not accumulated gradually but arise during a single event. The resulting structural variants are extensive and often cause oncogene activation or tumor suppressor inactivation. Chromothripsis is associated with many tumor types, especially with brain and bone tumors. Besides that, it has been described also in congenital disorders. The exact mechanism of chromothripsis origin has not been clarified yet; however, several hypotheses have been prosed, among which DNA damage in micronucleus seems to be most likely. Similarly, an impact of chromothripsis on cellular processes has not been fully understood, yet its association with unfavorable prognosis has been observed. PURPOSE: The purpose of this article is to summarize the current knowledge about chromothripsis and to present gathered pieces of information in a structured way. We focused on describing the basic features of chromothripsis, potential mechanisms of its origin, its impact on cellular processes and providing an overview of diseases where chromothripsis has been noted, with particular attention to cancer. Finally, we suggest a potential use of current knowledge about chromothripsis in the optimization of personalized treatment. Supported by Ministry of Health of the Czech Republic, grant no. 15-31834A. All rights reserved. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Submitted: 31. 12. 2018 Accepted: 19. 3. 2019.

Plasma Cell Leukemia ­â€Š the Forgotten Dis­ease

BACKGROUND: Plasma cell leukemia (PCL) is a rare dis-ease and possibly the most aggressive form of monoclonal gammopathy. It is classified into two forms -  primary PCL that occurs without a previously identifiable multiple myeloma stage, and secondary PCL that develops from previously dia-gnosed multiple myeloma. These two forms have different cytogenetic and molecular profiles, but both forms have an aggressive clinical course. Combinations of different therapeutic approaches includ-ing autologous stem cell transplantation and currently proteasome inhibitors and immunomodulatory drugs are used to treat PCL. Current dia-gnostic criteria, developed in the 1970s, may underestimate PCL prevalence; thus, prospective re-evaluation is be-ing considered. PURPOSE: The aim of this study is to review all available information about PCL with an emphasis on dia-gnostics, treatment, and circulat-ing plasma cells features. CONCLUSION: Although PCL is rare, it is quite a severe dis-ease. Current treatments us-ing the latest therapeutics have prolonged patient survival. However, due to the low incidence of PCL, information about the dis-ease is very limited and comes mostly from small retrospective studies. Further studies of PCL are needed, because new information could increase in patient survival and our understand-ing of its pathogenesis. Key words plasma cell leukemia -  multiple myeloma -  plasma cells -  cytogenetics -  treatment This work was supported by grant NV18-03-00203. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Submited: 2. 11. 2018 Accepted: 18. 11. 2018.

Allogeneic stem cell transplantation after fludarabine, melphalan and thymoglobulin followed by early withdrawal of prophylactic immunosuppression in patients with acute lymphoblastic leukemia - update of single center study.

Presented are updated results of allogeneic hematopoietic stem cell transplantations (HSCTs) in 25 adult patients with acute lymphoblastic leukemia (ALL) in complete remission (CR) after a reduced intensity conditioning (RIC) combining fludarabine (150 mg/m2) and melphalan (140 mg/m2) with thymoglobulin (4.5 mg/kg or recently 4.0 mg/kg) followed by early initiation of reduction and withdrawal of prophylactic posttransplant immunosuppression. The median post-transplant follow-up was 32 (range, 4-87) months. Stable engraftment of donor's hematopoiesis was achieved in all patients. Acute graft versus host disease (GVHD) as well as the chronic one were equally observed in four cases (16%). Five patients (20%) relapsed with ALL in the median of 9 (range, 3-15) months after HSCT. During the above post-transplant follow-up, 4 recipients (16%) died. Disease progression and posttransplant complications were the cause of death in three (12%) and one (4%) of them, respectively. The probabilities of 2-year event-free (EFS) and overall survival (OS) were 70.3% (95% CI 51.9-88.7%) and 86.1% (95% CI 71.6-100%), respectively. Presented study confirmed our previously reported promising results and this approach may be considered as an alternative to traditional HSCTs performed in high-risk patients with ALL.

Treatment and prognosis of childhood acute lymphoblastic leukemia on protocols ALL-BFM 90, 95 and ALL IC-BFM 2002: a retrospective single-center study from Olomouc, Czech Republic.

Great progress has been made in the diagnostics and treatment of childhood acute lymphoblastic leukemia (ALL) over the past decades. The vast majority of children are cured, however, there is need for further improvement, especially in specific patient subgroups. Our aim was to retrospectively evaluate disease characteristics and treatment outcomes of children with ALL enrolled in a single center into consecutive treatment protocols (ALL-BFM 90, ALL-BFM 95 and ALL IC-BFM 2002) between years 1990 and 2007 and comprehensively summarize diagnostic and therapeutic advances between protocols. In total, 97 patients aged 0 to 18 years were treated for ALL at University Hospital Olomouc in the Czech Republic and steadily high relapse-free survival (RFS), event-free survival (EFS) and overall survival (OS) were observed during the evaluated time period without significant difference between the protocols (RFS 80-86%, EFS 75-83% and OS 84-92%). In conclusion, our center has demonstrated survival rates comparable to leading international study groups for childhood ALL over a substantial period of time. This has been achieved namely due to advances in diagnostics, excellent collaboration on regional, national and international level, quality assurance and high overall standard of care. The acquired experience has been crucial for current participation in the best performing Berlin-Frankfurt-Münster (BFM)-based international trials for childhood ALL.

[Molecular Prognostic Markers and Their Clinical Relevance in Chronic Lymphocytic Leukemia]. / Molekulární prognostické markery chronické lymfocytární leukemie a jejich klinický význam.

Chronic lymphocytic leukemia is the most common leukemia in Western countries affecting particularly elderly adults. Despite the constantly improving therapy options, chronic lymphocytic leukemia is still an incurable disease owing to considerable clinical and bio-logical heterogeneity. Pathogenesis of chronic lymphocytic leukemia is not fully understood; however, aberrant antigenic stimulation, apoptosis deregulation and microenvironmental interactions play a crucial role in disease development. The most important molecular prognostic markers with clinical relevance include mutation status of heavychain immunoglobulin genes (IGHV), presence of cytogenetic aberrations and TP53 and ATM gene mutations. Recent implementation of next generation sequencing technologies has enabled more accurate analysis of both wellestablished and novel potential prognostic markers. The most relevant candidates are mutations in SF3B1, NOTCH1 and BIRC3 genes, which are now intensively studied with respect to their clinical importance. The other examined molecular mechanisms of chronic lympho-cytic leukemia pathogenesis include deregulation of B cell receptor signalization and abnormal regulation of gene expression by microRNA. The precise characterization of molecular abnormalities improves the risk stratification of chronic lymphocytic leukemia patients, which could possibly benefit from new treatment approaches.

Allogeneic stem cell transplantation after fludarabine, melphalan and thymoglobulin followed by early withdrawal of prophylactic immunosuppression could be an effective approach to patients with acute lymphoblastic leukemia.

Presented are results of allogeneic hematopoietic stem cell transplantations (HSCTs) in 13 patients with high-risk acute lymphoblastic leukemia (ALL) in the first complete remission after a reduced intensity conditioning combining fludarabine (150 mg/m2) and melphalan (140 mg/m2) with thymoglobulin (4.5 mg/kg). The immunosuppressive effect of T-cell depletion reducing the risk of graft-versus-host disease (GVHD) and non-relapse mortality was compensated by early initiation of reduction and withdrawal of prophylactic immunosuppression aimed at maintaining effective immunological antileukemic control. The median post-transplant follow-up was 23 (range, 10-65) months. Stable engraftment of donor's hematopoiesis was achieved in all patients. Acute GVHD was observed in two cases (15.4%); the chronic form was not noted. Two patients (15.4%) relapsed with ALL at 3 and 16 months after transplantation. During the above post-transplant follow-up, all 13 recipients were alive, with a probability of 2-year disease-free survival of 76.9% (95% CI 51-100%). Although the results were obtained with a small pilot study group it may be assumed that, given the prognostic risk of most patients and the nearly 2-year median post-transplant follow-up, the approach may be considered as an alternative to HSCTs after traditional myeloablative or reduced conditioning regimens with standard GVHD prophylaxis.

Biological and clinical characteristics of patients with chronic lymphocytic leukemia with the IGHV3-21 and IGHV1-69; analysis of data from a single center.

This study aimed at mapping the frequency of IGHV3-21 and IGHV1-69 in a group of 417 patients newly diagnosed with chronic lymphocytic leukemia (CLL) and described basic characteristics, cytogenetic abnormalities and prognosis of these patient subgroups. IGHV3-21 was found in 29 patients (7%) and IGHV1-69 in 51 patients (12.4%). The median overall survival (OS) rates were 97 months and 85 months in the IGHV3-21 and IGHV1-69 groups, respectively. In this small group of patients, the study failed to show a difference in OS of IGHV3-21 patients with mutated and unmutated IGHV status (p<0.597). There was also no difference in OS between IGHV3-21 patients with mutated IGHV status and all patients in the group having unmutated IGHV status (p<0.245). On the other hand, patients with IGHV3-21 and the presence of some other adverse prognostic factors (age ≥ 65 years, lymphocyte count ≥ 50×109/L, serum thymidine kinase ≥ 9U/L, deletion of 17p) had statistically significantly worse OS than IGHV3-21 patients without the presence of these prognostic factors. The multivariate analysis of an entire group of Binet clinical stage A patients proved that the presence of IGHV3-21 is as an independent adverse prognostic factor even though there was no statistical difference in OS between patients with IGHV3-21 and those without IGHV3-21 in the entire group (p<0.769). Patients with IGHV1-69 had the same probablility of OS irrespective of the presence of other adverse prognostic factors; their OS was significantly shorter as compared with the other patients from the entire group (p<0.03).The study mapped the occurrence of recurrent cytogenetic changes detected by FISH in IGHV3-21 (subset #2 and non-subset #2) and IGHV1-69 and compared it with the occurrence of recurrent changes in the entire group of patients. In IGHV1-69 and in subset #2 IGHV3-21, higher proportions of deletion of 11q were found (30% and 31%, respectively), with the deletion being present in 19.2% of the entire group of patients. None of the 3 patients with IGHV3-21 and deletion of 17p had subset #2. Patients with subset #2 IGHV3-21 had higher proportions of deletion of 13 (69%) as compared with non-subset #2 IGHV3-21 patients (27%).

Acute promyelocytic leukemia successfully treated also in elderly patients with significant comorbidities: a 20-year single-center experienc.

UNLABELLED: Acute promyelocytic leukemia is a unique entity among acute leukemias. Introduction of all-trans retinoic acid and, subsequently, arsenic trioxide in its treatment has markedly improved treatment outcomes for this once frequently fatal disease. Improved outcomes have also been observed in elderly patients, including those in whom standard intensive therapy is contraindicated because of comorbidities.In our center, a total of 60 APL patients were treated in 1993-2013, of whom 9 were aged 60 or more years. Although most of them had significant comorbidities at the time of diagnosis, eight achieved complete remission. At the time of the analysis, six patients were alive and in long-term remission; two patients died of causes other than APL. The median follow-up was 59 months.Included is case report of a patient with a high comorbidity score whose treatment was markedly reduced and individualized.Our experience shows that, in APL patients a curative approach is generally tolerated and should always be attempted regardless of age and comorbidities. KEYWORDS: APL - elderly patients - comorbidity.

Diffuse large B-cell lymphoma: the history, current view and new perspectives.

The basic principles of lymphoma classification(s) in general have been widely evolving in a course of decades of years wiht the use of contemporary resources and recent cutting edges in hematooncology on a clinical, morphological and molecular level bring new possibilities not only in improvements of diagnostic and prognostic algorithms and also bear new opportunities in so called targeted and tailored strategies of lymphoma therapy. The pathogenesis and biologic behavior of lymphoproliferations and even lymphomas should be studied in a context of lymphocytic and (neoplastic) lymphoid stage and chronologic development. In a current more complex insight into lymphoproliferations we would like to describe huge heterogeneity of diffuse large B-cell lymphoma in relationship to mandatory WHO classification since 2008 and the next development of knowledge in this field with potential new influence on an advancement of both classification and therapy.

The MLL recombinome of acute leukemias in 2013.

Chromosomal rearrangements of the human MLL (mixed lineage leukemia) gene are associated with high-risk infant, pediatric, adult and therapy-induced acute leukemias. We used long-distance inverse-polymerase chain reaction to characterize the chromosomal rearrangement of individual acute leukemia patients. We present data of the molecular characterization of 1590 MLL-rearranged biopsy samples obtained from acute leukemia patients. The precise localization of genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and novel TPGs identified. All patients were classified according to their gender (852 females and 745 males), age at diagnosis (558 infant, 416 pediatric and 616 adult leukemia patients) and other clinical criteria. Combined data of our study and recently published data revealed a total of 121 different MLL rearrangements, of which 79 TPGs are now characterized at the molecular level. However, only seven rearrangements seem to be predominantly associated with illegitimate recombinations of the MLL gene (≈ 90%): AFF1/AF4, MLLT3/AF9, MLLT1/ENL, MLLT10/AF10, ELL, partial tandem duplications (MLL PTDs) and MLLT4/AF6, respectively. The MLL breakpoint distributions for all clinical relevant subtypes (gender, disease type, age at diagnosis, reciprocal, complex and therapy-induced translocations) are presented. Finally, we present the extending network of reciprocal MLL fusions deriving from complex rearrangements.

FcγRIIIA receptor genotype does not influence an outcome in patients with follicular lymphoma treated with risk-adapted immunochemotherapy.

Antibody (rituximab) dependent cellular cytotoxicity is a key mechanism in killing CD20+ lymphoma cells. FcγRIIIA-158 V/F gene polymorphism results in expression of 3 variants of the FcγRIIIA receptor (FcγRIIIA) on cytotoxic lymphocytes with different receptor affinity. We studied 102 patients with newly diagnosed FL to assess whether the FcγRIIIA genotype influences outcome in patients treated with risk-adapted immunochemotherapy. The median age was 52 years (31-84); 90% of the patients had advanced (III/IV) clinical stages. The Follicular Lymphoma International Prognostic Index (FLIPI) scores were as follows: low 18.9%, intermediate 33.7% and high 47.4%. The front-line treatment was stratified according to the commonly used risk factors (FLIPI, beta-2-microglobuline and serum-Tyrosine-Kinase levels, bulky disease) into 3 treatment groups: (1) patients with FLIPI 0-1 treated with (R)-CHOP (51%), (2) patients under 60 (65) years of age with intermediate-risk disease (FLIPI 2) indicated for an intensive protocol (ProMACE-CytaBOM or sequential chemotherapy) (21%), and (3) patients under 60 (65) years with high-risk disease (FLIPI ≥3) treated with intensive chemotherapy plus autologous stem cell transplantation (28%). Rituximab was added to front-line chemotherapy in 59% of the patients. Generally, complete remission (CR) or unconfirmed CR was achieved in 85% of the patients, 11% had partial remission and 4% stable disease. Molecular CR (CRm) was achieved in 67.4% of 86 evaluable patients. Overall survival (OS) at 5 years reached 84% (95% CI 0.74-0.93); event-free survival (EFS) at 5 years was 58% (95% CI 0.45-0.71). The frequencies of FcγRIIIA-158 gene polymorphisms V/V, V/F and F/F were 8%, 50% and 42%, respectively. The FLIPI score distribution was not different in F/F patients as compared to V/F+V/V carriers (chi-square, P=0.7). The treatment modalities (treatment arm or rituximab administration) had the same distribution in V/V+V/F vs F/F patients (chi-square, P=0.16 and P=0.62, respectively). The CRm rates were similar in both subgroups of V/V+V/F vs F/F patients (chi-square, P=0.92). Survival curves for OS and EFS were not significantly different when comparing the subgroups of V/V+V/F vs F/F patients (P=0.28 and P=0.57, respectively). We found no difference in the quality of treatment response or survival after front-line immunochemotherapy between FcγRIIIA subgroups. FcγRIIIA polymorphism have no influence on the outcome of patients treated with risk-adapted chemotherapy with or without rituximab.

Prognostic factors and treatment outcome in 1,516 adult patients with de novo and secondary acute myeloid leukemia in 1999-2009 in 5 hematology intensive care centers in the Czech Republic.

Acute myeloid leukemia (AML) is a severe condition with a high mortality. When making decisions about the optimal tailor-made therapy, numerous prognostic factors are considered. The study represents a detailed analysis of the role of these factors and treatment outcomes based on a long-term follow-up of patients treated in 5 hematology intensive care centers in the Czech Republic.The studied group comprised 1,188 patients with de novo AML and 328 patients with secondary AML. The latter were significantly older, had more unfavorable cytogenetic changes and less frequently received curative therapy. Curatively treated patients achieved fewer complete remissions and relapsed more often than those with de novo AML. Patients with secondary AML had lower rates of allogeneic transplantation as part of consolidation therapy and a significantly shorter median overall survival. A lower proportion of the patients were alive at the time of analysis. However, the treatment outcome of de novo AML patients is not satisfactory, the only exception being those with acute promyelocytic leukemia. The analysis, which did not evaluate the intention-to-treat criteria and was without randomization, found allogeneic stem cell transplantation to be the most effective modality of consolidation therapy in both groups of patients. .

Dasatinib in imatinib-resistant or -intolerant CML patients: data from the clinical practice of 6 hematological centers in the Czech Republic.

Dasatinib is effective second line treatment for patients with chronic myeloid leukemia (CML) resistant or intolerant to imatinib. We report here the first experiences with dasatinib therapy in 71 CML patients resistant or intolerant to imatinib from the real clinical practice of 6 hematological centers in the Czech Republic. Dose 100 mg daily and 70 mg twice daily was administered to patients with chronic phase (CP) and advanced phases (AP) CML. In chronic phase (n=46), complete hematological reponse (CHR) was achieved in 97%, major cytogenetic reponse (MCgR) in 77% and complete cytogenetic response (CCgR) in 67%. Major molecular reponse (MMR) was achieved in 19/31 patients in median of 10 months. In advanced phase (n=25), CHR was attained in 77%, MCgR in 39%, CCgR in 33% and MMR in 2/18 patients. Eleven different baseline mutations were followed up in 15 patients. Dasatinib eliminated mutations in most of the patients, but 3 patients acquired a new one. Novel mutations were detected under dasatinib therapy in 2 patients. Dasatinib was well tolerated, cytopenias were common and was managed by dose modification. The estimated progression free survival (PFS) at 12 months was 97+/-3% in CP and 62+/-21% in AP. The median time to treatment failure was 605 days in AP while it was not reached in CP patients. Our clinical experiences, described here, confirmed that dasatinib is associated with high response rates especially in imatinib resistant or intolerant CML patients in chronic phase.

[Clinical relevance of chromosomal aberrations in bone and soft tissue tumors in children and young adults]. / Klinický význam chromozomálních zmen u nádoru kostí a mekkých tkání detí a mladistvých.

BACKGROUND: We present the results of a cytogenetic and molecular cytogenetic analysis of a series of patients with bone and soft tissue tumors. PATIENTS ANDMETHODS: We analyzed a cohort of 26 patients with Ewing sarcoma/PNET, 15 patients with rhabdomyosarcoma, 5 with synovial sarcoma and one patient with an undifferentiated sarcoma using the cytogenetic and molecular cytogenetic techniques M-FISH and arrayCGH. RESULTS: We found nonrandom chromosomal structural and numerical changes with diagnostic and prognostic relevance in most patients. Eight patients with ES/PNET had only a t(11;22)(q24;q12), eight patients had secondary aberrations as well and six had only secondary aberrations. In the RMS patients we detected the t(1;13)(p36;q14) once and the t(2;13)(q35;q14) four times, both of them characteristic for the alveolar subtype with poor prognosis and numerical aberrations, characteristic for the embryonal subtype, in five patients. Four patients with synovial sarcoma had the diagnostic t(X;18)(p11.2;q11.2), one of them had a complex karyotype with a complex t(X;18;21) (p11.2;q11.2;q11.2) together with t(2;5)(q24-32;p13-14) and t(12;20)(p11;q13). We correlated the karyotype of cancer cells with histopathologic morphologic analysis, clinical outcome and foreign published results. CONCLUSION: Cytogenetic and molecular cytogenetic analysis is a valuable diagnostic tool in bone and soft tissue tumors, especially in less differentiated subtypes, and as such it should be an integral part of curative care.

High-dose therapy and autologous stem cell transplantation in patients with diffuse large B-cell lymphoma in first complete or partial remission.

Improved survival has been observed in poor-risk diffuse large B-cell lymphoma (DLBCL) patients treated with high-dose therapy (HDT) followed by autologous stem cell transplantation (ASCT) in first complete remission. Retrospective studies have suggested that HDT with ASCT can improve survival also in partial responders but some doubts about the advantage of intensive therapy in such patients still remain. We evaluated retrospectively the results of HDT and ASCT in 55 patients with confirmed DLBCL treated between May 1999 and July 2006. Thirty-six patients (65%) showed partial remission (PR) and 19 patients (35%) reached complete remission (CR) after induction treatment with (44%) or without (56%) concomitant rituximab (R) immunotherapy. After HDT and ASCT, 69% of patients fulfilled the criteria of CR, 22% had unconfirmed CR (CRu), 7% remained in PR and 1 patient (2%) relapsed. Twenty patients in PR after the induction treatment reached CR after ASCT, 12 other PR patients achieved CRu. The 5-year event-free survival (EFS) of the 55 transplanted patients was 76% (95% confidence interval /CI/, 63% to 89%) and the 5-year overall survival (OS) was 85% (95% CI, 73% to 97%). The EFS and OS rates differed significantly only between patients younger than 40 years and older groups (p=0.022 and p=0.046, respectively). On univariate analysis of prognostic factors, EFS and OS were not affected by any of the following: age, sex, stage, subtype of DLBCL, initial lactate dehydrogenase, beta-2-microglobulin and serum thymidine kinase levels, International Prognostic Index (IPI) and age-adjusted IPI scores, induction treatment with or without rituximab and type of primary therapeutic response (CR vs PR). These results show that first-line HDT and ASCT for adults up to the age of 65 years with poor-risk DLBCL is a feasible and effective treatment option even in the era of R-chemotherapy in CR as well as for patients in PR.

Incidence of the main genetic markers in glioblastoma multiforme is independent of tumor topology.

Glioblastoma multiforme (GBM) is the most common as well as the most aggressive type of primary brain tumor of astrocytic origin in adults. GBM is characterized by a high degree of intratumoral heterogeneity both in histomorphology and genetic changes. Trisomy/polysomy of chromosome 7, monosomy of chromosome 10, EGFR gene amplification and p53 deletion have been described as the typical genetic markers for tumor classification and prediction of possible response to therapy. Our work was based on detection of these four main genetic changes both in central and peripheral parts of the tumors to evaluate possible differences in the topological incidence of these genetic markers. Chromosomal abnormalities in tumor samples from a group of 21 patients surgically treated for GBM were characterized by means of the interphase-fluorescence in situ hybridization (I-FISH) technique using sets of centromere and locus-specific DNA probes. In addition, we performed a detailed analysis of one selected tumor sample using a genomic microarray system (GenoSensor Array 300) to characterize copy number changes of specific sequences and refine results obtained by I-FISH. However, the data show no significant differences in occurrence of the described genetic markers in either part of the tumor.

[Chronic myeloid leukemia--resistance to imatinib mesylate (Glivec)--literature review and personal experience]. / Chronická myeloidní leukémie--rezistence na imatinib mesylát (Glivec)--prehled literatury a vlastní zkusenosti.

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by an abnormal fusion gene BCR-ABL. BCR-ABL encodes a constitutively active Bcr-Abl tyrosine kinase, which is required and sufficient for cellular transformation. Bcr-Abl is, therefore, an ideal target for pharmacotherapy. Imatinib Mesylate (Glivec) is a specific inhibitor of Bcr-Abl kinase. Imatinib shows high efficiency and low toxicity in treatment of CML patients. The main problem of imatinib treatment is the development of resistance. The mechanisms of resistance can be divided into two groups. The first group is characterized by reactivation of Bcr-Abl kinase in spite of continual imatinib presence. This can be caused by BCR-ABL amplification, overexpression or mutation in Abl kinase domain. Imatinib might not even reach the target Bcr-Abl protein (possible causes: drug efflux or imatinib binding to alpha1-acid glycoprotein). In the second group of resistance mechanisms, the Bcr-Abl kinase is inhibited but the resistance is maintained by other signal transducers (e.g. Src kinases). Standard cytogenetics as well as assay evaluating the phosphorylation status of Bcr-Abl substrate and/or sequencing of Abl kinase transcript can be used to test the mechanism of resistance. Treatment of patients can be re-evaluated on the basis of the status of IM resistance.

[Principle and importance of using the array CGH in hematooncology]. / Princip a význam metody arrayCGH v hemato-onkologii.

Identification of chromosomal changes and variation in DNA copy number allows us to understand pathogenesis of tumors. To the frequently diagnosed chromosomal changes belong acquired gains and losses of chromosomal regions carring genes involved in cellular proliferation and differentiation as well as oncogenes and tumor suppressor genes. The determination of gene changes is limited by techniques used for their identification. The introduction of genom-wide microarray technology, resolution has rapidly increased. Array comparative genomic hybridization (arrayCGH) offers higher resolution for genome-wide detection of chromosomal alteration and it is able to analyze hundreds to thousands of genes presented on microarray in one experiment. The aim of this study was to perform arrayCGH technology and to stress its value for the identification of chromosomal imbalances in hematological malignancies.