Detection of chimeric BCR-ABL genes in acute lymphoblastic leukaemia by the polymerase chain reaction

Systematic Review of Normal Subjects Harbouring BCR-ABL1 Fusion Gene

The treatment of chronic myeloid leukaemia (CML) requires quantitative polymerase chain reaction (qPCR) to monitor BCR-ABL1 in International Scale (IS). Some normal subjects were found to harbour BCR-ABL1. We performed a systematic review on normal subjects harbouring BCR-ABL1. A literature search was done on July 16, 2017 using EBSCOhost Research Databases interface and Western Pacific Region Index Medicus. Two authors selected the studies, extracted the data, and evaluated the quality of studies using the modified Appraisal Tool for Cross-Sectional Studies independently. The outcomes were prevalence, level of BCR-ABL1IS, proportion, and time of progression to CML. The initial search returned 4,770 studies. Eleven studies, all having used convenient sampling, were included, with total of 1,360 subjects. Ten studies used qualitative PCR and one used qPCR (not IS). The mean prevalence of M-BCR was 5.9, 15.5, and 15.9% in cord blood/newborns/infants (CB/NB/I) (n = 170), children (n = 90), and adults (n = 454), respectively, while m-BCR was 15, 26.9, and 23.1% in CB/NB/I (n = 786), children (n = 67), and adults (n = 208), respectively. No study reported the proportion and time of progression to CML. Nine studies were graded as moderate quality, one study as poor quality, and one study as unacceptable. The result of the studies could neither be inferred to the general normal population nor compared. Follow-up data were scarce.

The impact of immunological and biomolecular investigations on the outcome of children with acute lymphoblastic leukemia - experience of IIIrd Paediatric Clinic Timisoara

Introduction. The unsatisfactory results of the survival in patients with acute lymphoblastic leukemia (ALL) until 2000 in our center have led us to improve the approach of diagnosis and therapy. Since 2003 in all patients the following have been performed: flow cytometry, conventional genetic diagnosis, FISH (fluorescent in situ hybridization), and molecular biology. Objectives. Our aims were to identify solutions to increase patients’ survival. Patients and method. It is a single-center, retrospective study of 136 patients with ALL treated at 3rd Pediatric Clinic of Timisoara, over a period of 10 years (2003-2012), where survival was assessed. Results. Morphologically, 86% of the patients were L1 type, 13% L2 type and 1% L3 type. Flow citometry revealed that 68% were ALL with B precursors, and 19% with T immunophenotype. Acute leukemia with mixed phenotype (biphenotypic) was identified in 2.3% of patients and 10.7% of the forms were acute leukemia with myeloid markers. In 27.7% of patients, mutations were detected by the RT-PCR method, the most commonly identified was TEL-AML1 (ETV6- RUNX1) accounting for 12.7% of the cases. Relapse-free survival at 5 years for the entire group was 59%, and for the group treated between 2008 and 2012 it was 72%. Conclusion. Our analysis confirms the decisive value of laboratory investigations for the prognosis and improvement of supportive therapy.

Diagnostic and treatment of adult Philadelphia chromosome-positive acute lymphoblastic leukemia

The outcome of adult patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) has improved substantially with the introduction of tyrosine kinase inhibitors (TKIs). TKIs are now integral components of therapy for Ph+ ALL. The current consensus is that they improve patient outcomes compared with historical control patients treated with chemotherapy alone, and increase the number of patients able to receive stem cell transplant. New challenges have emerged with respect to induction of resistance mainly via Abelson tyrosine kinase mutations. Several novel kinase inhibitors with significantly more potent antileukemic activity are currently being developed. Furthermore novel immune therapies, which recruit or modify patient's own T cells to fight leukemic cells, are being developed and could find an important place in Ph+ ALL therapy by few years. In this article, we reviewed treatment approaches in adults with Ph+ ALL with a focus on TKIs and combined chemotherapy regimens.

The development of agents targeting the BCR-ABL tyrosine kinase as Philadelphia chromosome-positive acute lymphoblastic leukemia treatment

INTRODUCTION

In Philadelphia chromosome-positive (Ph⁺) acute lymphoblastic leukemia (ALL), the BCR-ABL translocation is the main transforming event; consequently, it is targeted by ABL-tyrosine kinase inhibitors (TKIs), the first of which to be identified was imatinib mesylate. There are now four newer TKIs, three so-called second-generation inhibitors and one third generation inhibitor, all of which are more potent than imatinib in in vitro assays. Areas covered: This paper reviews the current knowledge on the function of BCR-ABL. Furthermore, this paper highlights the impact of this knowledge on the development of a targeted therapy approach in Ph⁺ ALL and the obstacles for the successful treatment with these drugs. Expert opinion: Identifying key components involved in disease pathogenesis may lead to new approaches that might overcome resistance mediated to the BCR-ABL TKIs. In a near future, the authors believe that monoclonal antibodies and immunotherapy should also be combined with TKIs and up-front chemotherapy for the successful treatment of ALL.

Treatment of Relapsing Ph+ Acute Lymphoblastic Leukemia with Donor Leukocyte Infusion Followed by Quantitative Monitoring of Residual Disease

The case of a 34-year-old man with relapsing Ph+ acute lymphoblastic leukemia (ALL), which occurred five months after allogeneic bone marrow transplantation, is described. He was originally treated with aggressive chemotherapy, which put him in hematological remission, and he subsequently received donor leukocyte infusion (DLI) form the original donor. To assess the efficacy of this adoptive immunotherapy, we monitored minor-BCR/ABL (m-BCR/ABL) mRNA levels using the recently established real-time quantitative RT-PCR (RQ-PCR) assay. The results were compared with those obtained using conventional qualitative RT-PCR assays run in parallel. RQ-PCR, but not RT-PCR-based, minimum residual disease (MRD) detection showed a good correlation with the rapid changes documented during the post-DLI clinical course. Currently, six months after DLI, the patient continues to be in remission, which is consistent with the undetectable levels of m-BCR/ABL mRNA in the leukemic clone using RQ-PCR found in this study. Thus, monitoring of m-bcr/abl transcripts using RQ-PCR provides more useful information on a clinical assessment of MRD.

Evaluation of a novel multiplex RT-qPCR assay for the quantification of leukemia-associated BCR-ABL1 translocation

Although monitoring of BCR-ABL1 translocation has become an established practice in the management of chronic myeloid leukemia (CML), the detection limit of the BCR-ABL1 transcripts needs more standardization. The aim of the present study was to evaluate the clinical performances of a novel assay for the quantification of BCR-ABL1 fusion transcripts (e13a2 and e14a2) and ABL1 in a single reaction. This assay is based on the real-time reverse transcription polymerase chain reaction (RT-qPCR) in multiplex format. In a retrospective comparative clinical study performed in a reference laboratory, RNA was extracted from 48 CML patient blood samples with various BCR-ABL1/ABL1 ratios and RT-qPCR was performed using either MAScIR assay or the RT-qPCR simplex reference assay used in routine clinical testing. The comparative clinical results showed high qualitative and quantitative concordance (correlation coefficient >0.95) between MAScIR and the reference assays. The present study illustrates the utility of MAScIR assay as a sensitive, rapid, and cost-effective quantitative device to monitor the BCR-ABL1 ratios by RT-qPCR on whole blood of diagnosed Philadelphia chromosome-positive (Ph+) leukemia patients. This test could be used as an aid in the assessment of molecular response to available treatments.

Current and future management of Ph/BCR-ABL positive ALL

Following the introduction of targeted therapy with tyrosine kinase inhibitors (TKI) at the beginning of the past decade, the outcome of patients with Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph+ ALL) has dramatically improved. Presently, the use of refined programs with first/second generation TKI's and chemotherapy together with allogeneic stem cell transplantation allow up to 50% of all patients to be cured. Further progress is expected with the new TKI ponatinib, overcoming resistance caused by T315I point mutation, other targeted therapies, autologous transplantation in molecularly negative patients, therapeutic monoclonal antibodies like inotuzumab ozogamicin and blinatumomab, and chimeric antigen receptor-modified T cells. Ph+ ALL could become curable in the near future even without allogeneic stem cell transplantation, minimizing the risk of therapy-related death and improving greatly the quality of patients' life.

Philadelphia Chromosome-positive Acute Lymphoblastic Leukemia in the Elderly: Prognostic Factors and Treatment Outcome

Data on all patients diagnosed with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) aged 55 or older, seen in our institution over a 17-year period, were studied to determine the incidence and range of clinical and biological subtypes, and the outcome of different therapeutic approaches. Twenty-five Ph+ ALL cases (median age: 64 years) were diagnosed between 1986 and 2003 (28% of all B-lineage elderly ALL seen during this period). Karyotypic analysis was performed successfully in 22 cases, while 3 were only diagnosed by molecular biology analysis. All patients had B-cell lineage ALL. Co-expression of myeloid markers was observed in 20% of tested cases. One patient died before chemotherapy could be given. All other patients received "curative" treatment according to different protocols used during the period of study. Overall the complete remission (CR) rate was 76% (95% confidence interval, CI: 55-91%). Fifteen patients achieved CR after one course of chemotherapy and 4 patients after salvage therapy. Median disease-free survival (DFS) of the entire cohort was 5.6 months (95% CI: 4.5-8.4 months) and median overall survival was 10.1 months (95% CI: 7.9-13 months). In multivariate analysis, age>or=70 years was of poor prognostic value for achieving CR (p=0.05) and hyperleukocytosis at diagnosis was of poor prognostic value for overall survival (p=0.001). Overall survival duration was not significantly influenced by achieving CR. Ph+ ALL patients did not show a significant difference in terms of outcome as compared with Philadelphia-negative ALL patients. The very poor overall outcome in elderly patients with Ph+ ALL may be significantly improved by the introduction of imatinib mesylate into current treatment regimens.

Philadelphia chromosome-positive leukemia stem cells in acute lymphoblastic leukemia and tyrosine kinase inhibitor therapy

Leukemia stem cells (LSCs), which constitute a minority of the tumor bulk, are functionally defined on the basis of their ability to transfer leukemia into an immunodeficient recipient animal. The presence of LSCs has been demonstrated in acute lymphoblastic leukemia (ALL), of which ALL with Philadelphia chromosome-positive (Ph(+)). The use of imatinib, a tyrosine kinase inhibitor (TKI), as part of front-line treatment and in combination with cytotoxic agents, has greatly improved the proportions of complete response and molecular remission and the overall outcome in adults with newly diagnosed Ph(+) ALL. New challenges have emerged with respect to induction of resistance to imatinib via Abelson tyrosine kinase mutations. An important recent addition to the arsenal against Ph(+) leukemias in general was the development of novel TKIs, such as nilotinib and dasatinib. However, in vitro experiments have suggested that TKIs have an antiproliferative but not an antiapoptotic or cytotoxic effect on the most primitive ALL stem cells. None of the TKIs in clinical use target the LSC. Second generation TKI dasatinib has been shown to have a more profound effect on the stem cell compartment but the drug was still unable to kill the most primitive LSCs. Allogeneic stem cell transplantation (SCT) remains the only curative treatment available for these patients. Several mechanisms were proposed to explain the resistance of LSCs to TKIs in addition to mutations. Hence, TKIs may be used as a bridge to SCT rather than monotherapy or combination with standard chemotherapy. Better understanding the biology of Ph(+) ALL will open new avenues for effective management. In this review, we highlight recent findings relating to the question of LSCs in Ph(+) ALL.

Common leukemia- and lymphoma-associated genetic aberrations in healthy individuals

Leukemia- and lymphoma-associated (LLA) chromosomal rearrangements are critical in the process of tumorigenesis. These genetic alterations are also important biological markers in the diagnosis, prognosis, and treatment of hematopoietic malignant diseases. To detect the presence or absence of these genetic alterations in healthy individuals, sensitive nested RT-PCR analyses were performed on a large number of peripheral blood samples for selected markers including MLL partial tandem duplications (PTDs), BCR-ABL p190, BCR-ABL p210, MLL-AF4, AML1-ETO, PML-RARA, and CBFB-MYH11. Using nested RT-PCR, the presence of all of these selected markers was detected in healthy individuals at various prevalence rates. No correlation was observed between incidence and age except for BCR-ABL p210 fusion, the incidence of which rises with increasing age. In addition, nested RT-PCR was performed on a large cohort of umbilical cord blood samples for MLL PTD, BCR-ABL p190 and BCR-ABL p210. The results demonstrated the presence of these aberrations in cord blood from healthy neonates. To our knowledge, the presence of PML-RARA and CBFB-MYH11 in healthy individuals has not been previously described. The present study provides further evidence for the presence of LLA genetic alterations in healthy individuals and suggests that these mutations are not themselves sufficient for malignant transformation.

High prevalence of BCR-ABL fusion transcripts with poor prognostic impact among adult ALL patients: report from Pakistan

AIM

Philadelphia (Ph) chromosome positive acute lymphoblastic leukemia (ALL) is a common cytogenetic abnormality associated with poor outcome in adults. This preliminary study, in the absence of substantial evidence, reported the prevalence of the BCR-ABL gene fusion in ALL patients by RT-PCR in Pakistan. Moreover, the prognostic significance of BCR-ABL fusion along with other characteristics was also ascertained.

METHODS

One hundred forty six newly diagnosed ALL patients treated at our center between 2005 and 2008 comprised the study group. The patients were treated with a Children and Leukemia Group B induction regimen.

RESULTS

Among these patients, BCR-ABL fusion oncogene was present in 43 of 78 patients (55%). A statistically significant difference in BCR-ABL-positivity within three age groups (<20 years, 20-50 years, >50 years) was observed (P= 0.001). The median age was significantly higher in the BCR-ABL+ group (30 vs 19 years; P= 0.001). BCR-ABL+ patients were also characterized by higher median WBC counts (96,000/µL vs 23,000//µL, P= 0.002). Complete remission was achieved in 74% BCR-ABL- patients and 35% BCR-ABL+ patients (P= 0.001). Only 10% of BCR-ABL- patients achieved continued complete remission (CR). None of the BCR-ABL+ patients maintained a CR further to induction therapy. With the available therapeutic protocol, the presence of a BCR-ABL fusion predicted a lower survival (P= 0.001).

CONCLUSION

A high prevalence of BCR-ABL gene fusion was observed that appeared as a poor prognostic factor. Identification of this genetic entity at diagnosis is crucial for understanding the nature of adult ALL and for deciding optimal treatment.

Clinical outcome of children with newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia treated between 1995 and 2005

PURPOSE

In a previous analysis of 326 children with Philadelphia chromosome (Ph) -positive acute lymphoblastic leukemia (ALL) treated between 1986 and 1996, hematopoietic stem-cell transplantation from HLA-matched related donors, but not from unrelated donors, offered a superior outcome than chemotherapy alone. To evaluate the impact of recent improvements in chemotherapy and transplantation, we performed a similar analysis on patients treated in the following decade.

PATIENTS AND METHODS

We analyzed 610 patients with Ph-positive ALL treated between 1995 and 2005 without tyrosine kinase inhibitor therapy. The median follow-up duration was 6.3 years.

RESULTS

Complete remission was achieved in 89% of patients. The 7-year event-free survival and overall survival rates were superior in the present cohort compared with the previous cohort (32.0% ± 2.0% v 25.0% ± 3.0, respectively, P = .007; and 44.9% ± 2.2% v 36.0% ± 3.0%, respectively, P = .017). Compared with chemotherapy alone, transplantation with matched related donors or unrelated donors in first remission (325 patients) showed an advantage with increasing follow-up, suggesting greater protection against late relapses (hazard ratio at 5 years, 0.37; P < .001). In the multivariate Cox regression analysis accounting for treatment (transplantation v no transplantation), age, leukocyte count, and early response had independent impact on treatment outcome.

CONCLUSION

Clinical outcome of children and adolescents with Ph-positive ALL has improved with advances in transplantation and chemotherapy. Transplantations with matched related donors and unrelated donors were equivalent and offered better disease control compared with chemotherapy alone. Age, leukocyte count, and early treatment response were independent prognostic indicators. The results of this study will serve as a historical reference to evaluate the therapeutic impact of tyrosine kinase inhibitors on the outcome of Ph-positive ALL.

Mutation-specific control of BCR-ABL T315I positive leukemia with a recombinant yeast-based therapeutic vaccine in a murine model

Chromosomal translocations generating the BCR-ABL oncogene cause chronic myeloid leukemia (CML) and a subset of acute lymphoblastic leukemia. The BCR-ABL(T315I) mutation confers drug resistance to FDA-approved targeted therapeutics imatinib mesylate, dasatinib, and nilotinib. We tested the ability of a recombinant yeast-based vaccine expressing the T315I-mutated BCR-ABL antigen to stimulate an anti-BCR-ABL(T315I) immune response. The yeast-based immunotherapy significantly reduced or eliminated BCR-ABL(T315I) leukemia cells from the peripheral blood of immunized animals and extended leukemia-free survival in a murine model of BCR-ABL(+) leukemia compared to animals receiving sham injection or yeast expressing ovalbumin. With immunization, leukemic cells harboring BCR-ABL(T315I) were selectively eliminated after challenge with a mixed population of BCR-ABL and BCR-ABL(T315I) leukemias. In summary, yeast-based immunotherapy represents a novel approach against the emergence of cancer drug resistance by the pre-emptive targeted ablation of tumor escape mutants.

Expression of interleukin 15 in primary adult acute lymphoblastic leukemia

BACKGROUND

Interleukin-15 (IL-15) has been associated with the growth, survival and biological behavior of leukemic cells and response to therapy. We determined the expression of IL-15 in lymphoblasts and evaluated its potential impact on the outcome in adult acute lymphoblastic leukemia (ALL).

METHODS

Between June 1999 and June 2006, ALL samples were collected from 87 adult patients before initiation of antineoplastic therapy. These patients were enrolled in the German Multicenter Acute Lymphoblastic Leukemia June 1999 and July 2003 study trials. The expression of IL-15 in leukemic cells was analyzed by real-time polymerase chain reaction.

RESULTS

The expression of IL-15 correlated with the immunophenotype: T-lineage ALL had a more than 4-fold higher IL-15 mRNA expression as compared with B-cell precursor (BCP)-ALL (P < .001). Patients with BCR-ABL(+)-BCP-ALL had lower IL-15 expression compared with BCR-ABL(-)-BCP-ALL (P = .041). Furthermore, higher expression of IL-15 was associated with mediastinal (P = .001) and lymph node infiltration (P = .051), but not with hepatomegaly and splenomegaly. Notably, high IL-15 expression in BCP-ALL was associated with an inferior relapse-free survival (RFS) at 5 years (0.17 +/- 0.13 vs 0.47 +/- 0.13) (P = .008), but there was no impact on overall survival (P = .249).

CONCLUSIONS

Differential expression of IL-15 in adult ALL at diagnosis was associated with clinical features and outcome, in particular, RFS. It remains to be evaluated whether IL-15 might be a relevant therapy target, or might be used for risk stratification.

Aurora kinases and their inhibitors: more than one target and one drug

Dependent on the degree of inhibition of different Aurora kinase family members, various events in mitosis are affected, resulting in differential cellular responses. These different cellular responses have to be considered in the clinical development of the small molecule inhibitors with respect to the chosen indications, schedules and appropriate endpoints. Here the properties of the most advanced small molecule Aurora kinase inhibitors are compared and a case report on the development of PHA-739358 - a spectrum selective kinases inhibitor with a dominant phenotype of Aurora kinases inhibition, which is currently being tested in clinical trials - is discussed. One of the selection criteria for this compound was its property of inhibiting more than one cancer relevant target, such as Abl wild-type and the multidrug resistant Abl T315I mutant. This opens another path for clinical development in CML, and clinical trials are underway to evaluate the activity in patients suffering from chronic myelogenous leukemia, who developed resistance to currently approved treatments.

A multiplex PCR for improved detection of typical and atypical BCR-ABL fusion transcripts

RT-PCR is the method of choice for detecting BCR-ABL in CML and ALL. The three predominant mRNA transcripts found are e1a2 (in ALL), e13a2, and e14a2 (in CML and ALL). However, a number of "atypical"BCR-ABL transcripts (e1a3, e13a3, e14a3, e19a2, e6a2, e8a2, etc.) resulting from chromosomal breakpoints outside ABL intron 1 or BCR intron 1, 13 or 14, respectively, have been reported. These atypical transcripts may escape detection when using methods that are optimized to detect just the typical ones. We present here a novel, fast, and reliable multiplex PCR for improved detection of typical and atypical BCR-ABL transcripts.

Outcome of treatment in adults with Philadelphia chromosome-positive and/or BCR-ABL--positive acute lymphoblastic leukemia-retrospective analysis of Polish Adult Leukemia Group (PALG)

Patients with Philadelphia chromosome-positive (Ph+) and/or BCR-ABL+ acute lymphoblastic leukemia (ALL) have extremely poor prognoses. Most of these patients have additional, heterogenous karyotype abnormalities, the majority of which have uncertain clinical significance. In this study we analyzed the clinical characteristics, karyotype abnormalities, and outcome of 77 patients with Ph+ and/or BCR-ABL+ ALL registered in Poland in 1997-2004. In 31/55 patients with known karyotype, the sole t(9;22)(q34;q11) abnormality had been diagnosed; in one patient, variant translocation t(4;9;22)(q21q31.1;q34;q11), and additional abnormalities in 23 (42%) patients, had been diagnosed. The characteristics of the patients with Ph chromosome and additional abnormalities were not significantly different when compared with the entire analyzed group. Out of 77 patients, 54 (70%) achieved first complete remission (CR1) after one or more induction cycles. The overall survival (OS) probability of 2 years was 63, 43, and 17% for patients treated with allogeneic stem cell transplantation (alloSCT), autologous SCT, and chemotherapy, respectively (log rank p=0.002). Median OS from the time of alloSCT was significantly longer for patients transplanted in CR1 compared with alloSCT in CR >1 (p=0.032). There were no significant differences in CR rate, disease-free survival (DFS), and OS for patients with t(9;22) and additional abnormalities compared with the whole group. Only WBC >20 G/l at diagnosis adversely influenced OS probability (log rank p=0.0017). In conclusion, our data confirm poor outcome of Ph+ and/or BCR-ABL+ ALL. Only patients who received alloSCT in CR1 had longer DFS and OS. We have shown that additional karyotype abnormalities did not influence the clinical characteristics of the patients; however, their influence on treatment results needs to be further assessed.

Jumping translocation of 17q11∼qter and 3q25∼q28 duplication in a variant Philadelphia t(9;14;22)(q34;q32;q11) in a childhood chronic myelogenous leukemia

The virtually obligatory presence of the Philadelphia chromosome may suggest a causal homogeneity, but chronic myelogenous leukemia (CML) is a clinically heterogeneous disease. This may be a consequence of the variable BCR breakpoints on chromosome 22 and of nonrandom secondary chromosomal abnormalities. We present the case of a boy, age 12, investigated in blastic phase of CML. Karyotyping with conventional and multiplex fluorescence in situ hybridization (FISH and M-FISH) karyotyping, complemented with reverse transcriptase-polymerase chain reaction, identified a variant Philadelphia translocation t(9;14;22)(q34;q32;q11) involving a cryptic BCR/ABL fusion with formation of the p190(Bcr-Abl) oncoprotein. M-FISH revealed also an unbalanced jumping translocation of 17q11 approximately qter alternatively present on chromosomes 14 or 20, apparently hithertofore unreported in hematological malignancies. Another secondary aberration, dup(3)(q25q28), was revealed by multipoint interphase FISH (mpI-FISH). Gain of this region is known in adult hematological malignancies and solid tumors, suggesting its general involvement in tumor initiation or progression (or both), regardless of tissue origin.

The effect of first-line imatinib interim therapy on the outcome of allogeneic stem cell transplantation in adults with newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia

Previously, we suggested that imatinib incorporation into conventional chemotherapy as an alternative (imatinib interim therapy) might be a useful strategy for bridging the time to allogeneic stem cell transplantation (SCT) for newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL). Here, we provide an updated report on this strategy in 29 patients. At the time of enrollment, 23 patients (79.3%) achieved complete remission (CR). After the first imatinib cycle, the median breakpoint cluster region-Abelson oncogene locus (BCR-ABL)/ABL ratios decreased by 0.77 log in 25 (86.2%) responders, and their BCR-ABL/ABL ratios decreased further by 0.34 log after the second imatinib cycle, which included 7 molecular CR. One patient (4.3%) relapsed during the imatinib therapy. The remaining 3 patients were primarily refractory to both imatinib and chemotherapy. Twenty-five (86.2%) of the 29 patients received transplants in first CR. With a median follow-up duration of 25 months after SCT, the 3-year estimated probabilities of relapse, nonrelapse mortality, disease-free survival, and overall survival were 3.8%, 18.7%, 78.1%, and 78.1%, respectively. In comparison to our historical control data, first-line imatinib interim therapy appears to provide a good quality of CR and a survival advantage for patients with Ph(+) ALL. Further long-term follow-up is needed to validate the results of this study.

Reduced-intensity conditioning using TBI (8 Gy), fludarabine, cyclophosphamide and ATG in elderly CML patients provides excellent results especially when performed in the early course of the disease

Allogeneic bone marrow or stem cell transplantation is a curative therapeutic option for chronic myelogenous leukemia. In order to decrease the toxicity of the procedure, the dosage of total body irradiation was reduced from 12 to 8 Gy and subsequently the dose of cyclophosphamide from 120 to 80 mg/kg. The purine analogue fludarabine, ATG, cyclosporine A and a short course of methotrexate were given for immune suppression. So far, 35 elderly CML patients with sibling and unrelated donors have been transplanted. Transplant-related mortality at day + 100 was 11%. After engraftment, all patients achieved a complete cytogenetic remission. Relapse occurred in 14% of the patients. The risk of relapse was significantly higher in those patients transplanted in second chronic or accelerated phase (P = 0.048). After a median follow-up of 30 months (range 12-62), 63% of the patients are alive. Those patients transplanted within the first year from diagnosis had an overall survival of 79% (P = 0.049), emphasizing the benefit of early transplantation. Stepwise reduction of conditioning intensity resulted in stable engraftment, low relapse rates and encouraging overall survival in this high-risk patient group.

Poor correlation of kinetics between BCR-ABL and WT1 transcript levels after allogeneic stem cell transplantation

After allogeneic stem cell transplantation (SCT), we evaluated the use of the Wilms' tumor gene (WT1) as a minimal residual disease (MRD) marker in 32 patients (28 chronic myeloid leukemia, three acute lymphoblastic leukemia and one acute myeloid leukemia). All patients expressed BCR-ABL and the kinetics of WT1 were compared with those of BCR-ABL using real-time quantitative PCR. WT1 expression was seen in the peripheral blood (PB) of healthy controls with a median expression level of 7 x 10(-5) (WT1/ABL ratio). The corresponding values for BCR-ABL-negative and BCR-ABL-positive patient samples were 1 x 10(-4) and 1.6 x 10(-4), respectively. Kinetic studies in individual patients showed that WT1 and BCR-ABL levels usually did not copy each other. In four out of six patients who relapsed, an increase in WT1 from the background level (10(-4)) was observed only at the time of or after relapse, and in two patients increasing WT1 levels were observed before the relapse. In addition, the WT1 values found at the time of relapse were only two logs higher than the background level, indicating a sensitivity of 10(-2). In conclusion, there is a constitutive low expression of WT1 in normal hematopoietic cells. The sensitivity and ability of WT1 to predict a relapse were poor in this study.

Secondary cytogenetic aberrations in childhood Philadelphia chromosome positive acute lymphoblastic leukemia are nonrandom and may be associated with outcome

Additional chromosomal aberrations occur frequently in Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia (ALL) of childhood. The treatment outcome of these patients is heterogeneous. This study assessed whether such clinical heterogeneity could be partially explained by the presence and characteristics of additional chromosomal abnormalities. Cytogenetic descriptions were available for 249 of 326 children with Ph+ ALL, diagnosed and treated by 10 different study groups/large single institutions from 1986 to 1996. Secondary aberrations were present in 61% of the cases. Chromosomes 9, 22, 7, 14, and 8 were most frequently abnormal. Most (93%) karyotypes were unbalanced. Three main cytogenetic subgroups were identified: no secondary aberrations, gain of a second Ph and/or >50 chromosomes, or loss of chromosome 7, 7p, and/or 9p, while other secondary aberrations were grouped as combinations of gain and loss or others. Of the three main cytogenetic subgroups, the loss group had the worst event-free survival (P=0.124) and disease-free survival (P=0.013). However, statistical significance was not maintained when adjusted for other prognostic factors and treatment. Karyotypic analysis is valuable in subsets of patients identified by molecular screening, to assess the role of additional chromosomal abnormalities and their correlation with clinical heterogeneity, with possible therapeutic implications.

Paucity of TEL-AML 1 translocation, by multiplex RT-PCR, in B-lineage acute lymphoblastic leukemia (ALL) in Indian patients

A total of 69 patients of B lineage ALL, 35 children (32 males, 3 females) and 34 young adults (27 males, 7 females) were studied by multiplex RT-PCR to determine the relative frequency of t(9;22), t(12;21), t(1;19), and t(4;11,). Translocation (9;22) was seen in 1/35 (2.8%) and t(1;19) in 2/35 (5.7%) children. None of the children showed t(12;21) and t(4;11) translocations. In young adults, t(9;22) and t(1;19) were seen in 5/34 (14.7%) and 2/34 (5.8%) patients, respectively. None of the latter showed t(12;21) or t(4;11) translocations. Thus, there appears to be a significant under representation of the fusion transcripts for TEL-AML, a good prognostic marker, in this study, unlike in the West, where it is seen in 35% of children with ALL. This, together with the generally increased leukemic burden seen in Indian patients, may explain in part, the poor treatment outcome reported.

Specific killing of Ph+ chronic myeloid leukemia cells by a lentiviral vector-delivered anti-bcr/abl small hairpin RNA

Chronic myeloid leukemia (CML) is characterized by a reciprocal chromosomal translocation between chromosomes 9 and 22 t(9;22)(q34;q11) that causes fusion of the bcr and abl genes. Transcription and splicing of the fusion gene generate two major splice variants of the bcr/abl transcript that encode an oncoprotein with tyrosine kinase activity. We have taken advantage of lentiviral vectormediated delivery of anti-bcr/abl short hairpin RNAs (shRNA) to downregulate the bcr/abl transcript in Philadelphia chromosome-positive (Ph+) K562 leukemia cells. This downregulation caused complete inhibition of proliferation of these cells and was accompanied by >90% inhibition of the bcr/abl transcript and p210 protein. These results demonstrate the feasibility of using a lentiviral vector to stably transduce therapeutic shRNAs into leukemia cells for the potential ex vivo purging of Ph+ cells in an autologous hematopoietic cell transplant setting. Furthermore, the robust expression of the shRNAs from our lentiviral vector suggests that this system could be generally useful for the expression of other shRNAs.

Early prediction of response in patients with relapsed or refractory Philadelphia chromosome–positive acute lymphoblastic leukemia (Ph+ALL) treated with imatinib

Imatinib has pronounced but brief antileukemic activity in advanced Philadelphia chromosome–positive acute lymphoblastic leukemia (Ph+ALL). We assessed the prognostic impact of pretreatment disease features and the early bone marrow (BM) response in 68 consecutive patients with Ph+ALL receiving imatinib salvage therapy. A complete hematologic or marrow response was achieved by 92% of patients with BM blasts below 5% on day 14, whereas 62.5% of patients with more than 5% BM blasts on day 14 were nonresponders. Similarly, time to progression (TTP) was superior in patients with a good day 14 response (5.2 versus 0.9 months; P &lt; .0001). Prior complete remission of less than 6 months, white blood cell count of more than 10 × 109/L, circulating peripheral blood blasts at diagnosis, additional Philadelphia chromosomes, or at least 2 Bcr-Abl fusion signals were associated with significantly inferior remission rate and response duration. In patients without poor prognostic features, single-agent imatinib may be appropriate before transplant salvage therapy. Conversely, patients with clinically or cytogenetically defined poor-risk features are candidates for trials of upfront imatinib in combination with other agents.

Chronic myeloid leukemia: pathophysiology, diagnostic parameters, and current treatment concepts

Chronic myeloid leukemia (CML) is a stem cell disease characterized by excessive accumulation of clonal myeloid (precursor) cells in hematopoietic tissues. CML cells display the translocation t(9; 22) that creates the bcr/abl oncogene. The respective oncoprotein (= BCR/ABL) exhibits constitutive tyrosine kinase activity and promotes growth and survival in CML cells. Clinically, CML can be divided into three phases: the chronic phase (CP), the accelerated phase (AP), and the blast phase (BP) that resembles acute leukemia. Progression to AP and BP is associated with occurrence of additional genetic defects that cooperate with bcr/abl in leukemogenesis and lead to resistance against antileukemic drugs. The prognosis in CML is variable depending on the phase of disease, age, and response to therapy. The only curative approach available to date is stem cell transplantation. For those who cannot be transplanted, the BCR/ABL tyrosine kinase inhibitor STI571 (Glivec, Imatinib), interferon-alpha (with or without ARAC), or other cytoreductive drugs are prescribed. Currently available data show that STI571 is a superior compound compared to other drugs in producing complete cytogenetic and molecular responses. However, despite superior initial data and high expectations for an effect on survival, long term results are not available so far, and resistance against STI571 has been reported. Forthcoming strategies are therefore attempting to prevent or counteract STI571 resistance by co-administration of other antileukemic drugs. Whether these strategies will lead to curative drug therapy in CML in the future remains at present unknown.

Minimal residual disease-based role of imatinib as a first-line interim therapy prior to allogeneic stem cell transplantation in Philadelphia chromosome-positive acute lymphoblastic leukemia

Fourteen adults with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) were studied to evaluate the role of imatinib prior to allogeneic stem cell transplantation (SCT). Of these, 12 patients were in complete hematologic response (CHR), and 2 were refractory. Imatinib was administered as an interim schedule after each chemotherapy course. After the first imatinib cycle, 11 patients remained in sustained CHR with a decrease in the BCR-ABL/ABL ratios (0.89 logs), and one refractory patient achieved CHR. Meanwhile, 2 patients were resistant to imatinib. Ten patients receiving a second imatinib cycle following consolidation showed sustained CHR, including 2 molecular CR, with a further decrease in the BCR-ABL/ABL ratios (0.19 logs). Twelve patients underwent SCT in a favorable status, and of these, 11 are still alive in a leukemia-free status at 9 to 28+ months after SCT. First-line imatinib interim therapy appears to be a useful strategy to bridge the time to SCT for patients with Ph+ ALL.

Serial minimal residual disease (MRD) analysis as a predictor of response duration in Philadelphia-positive acute lymphoblastic leukemia (Ph+ALL) during imatinib treatment

Patients with refractory or relapsed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL) rarely have prolonged responses to salvage therapy, including imatinib, resulting in a short opportunity for potentially curative stem cell transplantation. To identify minimal residual disease (MRD) parameters predictive of imminent relapse, we quantitated Bcr-Abl expression by real-time PCR in peripheral blood (PB) and bone marrow (BM) of 24 Ph+ALL patients after achieving a complete response and MRD minimum. The ratio of Bcr-Abl and glyceraldehyde-3-phosphate dehydrogenase copies, magnitude of increase and velocity of increase were evaluated regarding subsequent time intervals to relapse, death or censoring. High Bcr-Abl levels >/=5 x 10(-4) in PB (n=23) and >/=10(-4) in BM (n=18) were significantly associated with short time periods to relapse. Bcr-Abl increases >2 logarithmic units (log) in PB, but not in BM preceded short-term relapse. The velocity of Bcr-Abl increases predicted response duration in PB (cutoff: 1.25 log/30 days) and BM (0.6). Bcr-Abl level and velocity of increase in BM as well as magnitude of increase in PB correlated with remaining periods of survival and predicted relapse within 2 months in nine of 10, 10 of 11 and four of four patients, respectively. Thus, these MRD parameters may guide timing and intensity of therapeutic modifications.

Expression of the human homologue of rat NG2 in adult acute lymphoblastic leukemia: close association with MLL rearrangement and a CD10(-)/CD24(-)/CD65s(+)/CD15(+) B-cell phenotype

The expression of the chondroitin sulfate proteoglycan neuron-glial antigen 2 (NG2) has been demonstrated in association with rearrangement of the mixed lineage leukemia (MLL) gene in acute leukemia, but the frequency of NG2 expression in adult acute lymphoblastic leukemia (ALL) is yet unknown. We evaluated NG2 expression in 313 adult ALL patients by flow cytometry and simultaneously determined MLL rearrangement in 120 adult patients out of them with B-precursor ALL by reverse transcription-polymerase chain reaction and fluorescence in situ hybridization. A total of 57% of pro-B ALL, 2% of common ALL and 20% of pre-B ALL were NG2 positive, but NG2 was absent in T-ALL and mature B-ALL. In B-precursor ALL, NG2 expression was significantly associated with a CD10(-)/CD34(-)/CD24(-)/CD65s(+)/CD15(+)/CD13(-)/CD33(-) phenotype and showed a sensitivity, specificity and positive predictive value of 0.89, 0.89, and 0.93 for MLL rearrangement, respectively. NG2 was positive in three patients without detectable MLL rearrangement and negative in eight patients with MLL-AF4 transcripts. However, NG2 predicted with a 100% accuracy MLL rearrangement among patients disclosing a CD65s(+) and/or CD15(+) immunophenotype. In summary, NG2 adds to a more precise identification of high-risk adult ALL and should therefore be included into diagnostic marker panels. As NG2 is negative in non-malignant hematopoietic cells, this novel antigen might also serve in future studies as a powerful marker in monitoring minimal residual disease.

A potential graft-versus-leukemia effect after allogeneic hematopoietic stem cell transplantation for patients with Philadelphia chromosome-positive acute lymphoblastic leukemia: results from the French Bone Marrow Transplantation Society

SUMMARY

Philadelphia chromosome (Ph) acute lymphoblastic leukemia-positive (ALL) is a subgroup of ALL with a poor prognosis. We sought to evaluate the results of allogeneic hematopoietic stem cell transplantation (HSCT) in this situation. From 1992 to 2000, 121 patients with Ph- positive ALL enrolled in one of the three main French prospective ALL chemotherapy trials and receiving allogeneic HSCT were reported to the registry of the French Society of Bone Marrow Transplantation (SFGM-TC). The median age was 35 years (range, 1-53). In all, 76 patients received HSCT in first complete remission and 45 in a more advanced disease stage. Minimal residual disease was evaluated just before the graft: 35 patients of the 52 patients in first remission had persistent BCR-ABL transcript detectable while 17 had no detectable minimal residual disease. Bone marrow and/or peripheral blood samples from 94 patients were submitted for reverse transcriptase polymerase chain reaction analysis at variable points after transplantation. Estimated 2-year survival and relapse rate for patients in CR1 were 50 and 37%, respectively, significantly better than for patients with more advanced disease (P=0.0001 and 0.01, respectively). There was no difference in survival or in relapse rates in terms of the donor used. Relapse was the most common cause of treatment failure. Hematological status at the time of transplant and the occurrence of acute graft-versus-host disease (GvHD) were the only two prognostic factors identified for relapse (P=0.02 and 0.02, respectively). Detection of BCR-ABL transcripts after transplantation had a predictive value on relapse occurrence. Finally, donor lymphocyte infusions were successfully used to treat some relapses. The graft-versus-leukemia effect of HSCT in Ph-positive ALL appears to be supported by (1) the lack of prognostic significance of pretransplant BCR-ABL transcript detection, (2) the efficacy of donor lymphocyte infusions in cases of relapse, and (3) the role of GvHD as protecting against relapse.

Risk factors for adults with Philadelphia-chromosome-positive acute lymphoblastic leukaemia in remission treated with allogeneic bone marrow transplantation: the potential of real-time quantitative reverse-transcription polymerase chain reaction

The aim of this study was to evaluate the outcomes for Philadelphia-chromosome-positive acute lymphoblastic leukaemia (Ph+ ALL) patients in remission treated with allogeneic bone marrow transplantation (BMT). Twenty-three adults were entered onto this study. The 2-year probabilities of relapse and disease-free survival (DFS) were 39.4 +/- 11.6% and 43.5 +/- 10.3% respectively. The presence of chronic graft-versus-host disease (GVHD) was found to be an independent predictive factor affecting lower relapse and DFS. To monitor the BCR-ABL transcript, we also analysed 48 bone marrow samples of eight patients using real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR). The kinetics of the BCR-ABL transcript correlated well with the patients' clinical course. In six patients who were in continuous remission after BMT, a rapid decrease in BCR-ABL copy number to the PCR-negative status was observed after the development of chronic GVHD. Meanwhile, routine bone marrow examination of two patients showed PCR positivity with a 3 or 4-log increase of BCR-ABL copy number and subsequent haematological relapse, which occurred 2 and 4 months later respectively. Although our data should be interpreted cautiously, the presence of chronic GVHD may reduce the risk of relapse in Ph+ ALL. Real-time quantitative RT-PCR appears to be a useful test for BCR-ABL transcript monitoring.

BCR/ABL genes and leukemic phenotype: from molecular mechanisms to clinical correlations

The Philadelphia chromosome (Ph), a minute chromosome that derives from the balanced translocation between chromosomes 9 and 22, was first described in 1960 and was for a long time the only genetic lesion consistently associated with human cancer. This chromosomal translocation results in the fusion between the 5' part of BCR gene, normally located on chromosome 22, and the 3' part of the ABL gene on chromosome 9 giving origin to a BCR/ABL fusion gene which is transcribed and then translated into a hybrid protein. Three main variants of the BCR/ABL gene have been described, that, depending on the length of the sequence of the BCR gene included, encode for the p190(BCR/ABL), P210(BCR/ABL), and P230(BCR/ABL) proteins. These three main variants are associated with distinct clinical types of human leukemias. Herein we review the data on the correlations between the type of BCR/ABL gene and the corresponding leukemic clinical features. Lastly, drawing on experimental data, we provide insight into the different transforming power of the three hybrid BCR/ABL proteins.

Prospective molecular monitoring of BCR/ABL transcript in children with Ph+ acute lymphoblastic leukaemia unravels differences in treatment response

Children with Philadelphia-chromosome-positive (Ph+) acute lymphoblastic leukaemia (ALL) represent a subgroup at very high risk for treatment failure, despite intensive chemotherapy. However, recent retrospective studies showed that Ph+ childhood ALL is a heterogeneous disease with regard to treatment response. We have prospectively monitored, by reverse transcription polymerase chain reaction (RT-PCR) during follow-up, the presence of the BCR/ABL fusion transcript in Ph+ ALL children diagnosed in the Italian multicentre Associazione Italiana Ematologia Oncologia Pediatrica ALL-AIEOP-95 therapy protocol. To our knowledge, this is the first report on the evaluation of minimal residual disease (MRD) in childhood Ph+ ALL prospectively enrolled in an intensive, Berlin-Frankfurt-Munster (BFM)-type treatment protocol. Twenty-seven of 36 (75.0%) Ph+ patients consecutively enrolled into the high-risk group of the AIEOP-ALL protocol between May 1995 and October 1999 were successfully analysed. Twenty were good responders to the pre-phase of prednisone/intrathecal methotrexate treatment (PGR) and seven were poor responders (PPR). Within the PPR group, the RT-PCR monitoring constantly showed positivity for the BCR/ABL fusion transcript and all the patients died of disease progression. In contrast, highly sensitive qualitative RT-PCR monitoring revealed heterogeneity within the PGR group of Ph+ childhood ALL patients. Three different subgroups could be defined, according to the clearance of Ph+ cells within the first 5 months of treatment. This provides useful information on the capability of chemotherapy to reduce the leukaemic clone, with prognostic implications.

Killing of leukemic cells with a BCR/ABL fusion gene by RNA interference (RNAi)

Short 21-mer double-stranded RNA (dsRNA) molecules have recently been employed for the sequence-specific silencing of endogenous human genes. This mechanism, called RNA interference (RNAi), is extremely potent and requires only a few dsRNA molecules per cell to silence homologous gene mRNA expression. We used dsRNA targeting the M-BCR/ABL fusion site to kill leukemic cells with such a rearrangement. Transfection of dsRNA specific for the M-BCR/ABL fusion mRNA into K562 cells depleted the corresponding mRNA and the M-BCR/ABL oncoprotein. This was demonstrated by real-time quantitative PCR and Western blots. The BCR/ABL knockdown was accompanied by strong induction of apoptotic cell death. Leukemic cells without BCR/ABL rearrangement were not killed by M-BCR/ABL-dsRNA. In addition, to corroborate the extraordinary sequence specificity of RNAi, we designed another RNA oligo matching the M-BCR/ABL fusion site but having two point mutations within its central region. We show that these two point mutations abolished both p210 reduction and induction of apoptosis in K562 cells. Finally, we compared leukemic cell killing by RNAi to that caused by the ABL kinase tyrosine inhibitor, STI 571, Imatinib. For full induction of apoptosis, dsRNA targeting M-BCR/ABL required 24 h more than Imatinib. This may be caused by the relatively long half-life of the BCR/ABL oncoprotein, which is not targeted by the RNAi mechanism, but is affected by STI 571. When we applied ds M-BCR/ABL RNA and STI 571 in combination, we did not observe a further increase in the induction of apoptosis. Nevertheless, these data may open a field for further studies towards gene-therapeutic approaches using RNA interference to kill tumor cells with specific genetic abnormalities.

Quantification of minimal residual disease in patients with e1a2 BCR-ABL-positive acute lymphoblastic leukemia using a real-time RT-PCR assay

Using a real-time RT-PCR method, we analyzed the expression of e1a2 BCR-ABL mRNA in bone marrow samples from 13 patients with e1a2 BCR-ABL-positive acute lymphoblastic leukemia (ALL) at different time points during chemotherapy and after bone marrow transplantation (BMT). The detection limit of the method, assessed using serial dilutions of ALL/MIK cells, was found to be 1:10(5), similar to what is observed for the conventional RT-nested PCR method. The e1a2 BCR-ABL values were normalized with respect to those of the housekeeping gene GAPDH. The decrease in the e1a2 BCR-ABL/GAPDH ratio after remission induction chemotherapy reflects well the response to chemotherapy and consequently correlates with the prognosis. Although molecular remission was achieved by chemotherapy alone, some patients relapsed, and the e1a2 BCR-ABL/GAPDH ratios in these cases progressively increased to the levels seen prior to hematological relapse. Long-term hematological complete remission (more than 30 months) could be achieved in cases in which a more than 4.0 log decrease in the e1a2 BCR-ABL/GAPDH ratio was obtained by chemotherapy alone, and BMT was then performed. In conclusion, real-time RT-PCR allows for an evaluation of the kinetics of e1a2 BCR-ABL/GAPDH expression during the various phases of chemotherapy or after BMT and may be effective for the indication and control of disease relapse in Ph-positive ALL patients.

Monitoring minimal residual disease using chromosomal translocations in childhood ALL

Clonal chromosomal abnormalities have been identified in approximately 80% of childhood ALL. In most instances the genes disrupted by these abnormalities have been identified, thus providing important insights into disease pathogenesis and normal cellular physiology. Polymerase chain reaction (PCR) amplification of fusion transcripts resulting from chromosomal translocations has emerged as a sensitive and reproducible method to monitor minimal residual disease (MRD) in childhood ALL. The measure of the initial response to therapy in patients who have achieved complete remission by morphological standards can dissect clinical heterogeneity within the genetically homogeneous childhood ALL subgroup. Moreover, MRD monitoring can be applied to predict impending relapses early. Despite notable progress with this method, several critical issues must be resolved before MRD determinations can be routinely considered in clinical decision making. This chapter will focus on the main progress and common pitfalls in the PCR detection of chromosomal translocations applied to clinical studies.

Detection of minimal residual disease

A high percentage of patients with leukemia, lymphoma, and solid tumors achieve a complete clinical remission after initial treatment, but the majority of these patients will finally relapse from residual tumor cells detectable in clinical remission only by the most sensitive methods. The in vitro amplification of tumor-specific DNA or RNA sequences by polymerase chain reaction (PCR) allows identification of a few neoplastic cells in 10(4) to 10(6) normal cells. Depending on the underlying malignant disease and therapeutic treatment, the presence of residual tumor cells in an individual patient may herald relapse, but a long-term stable situation or slowly vanishing tumor cells are also possible. Molecular monitoring of residual leukemia and lymphoma cells by quantitative PCR techniques has provided important information about the effectiveness of treatment and the risk of recurrent disease as shown by minimal residual disease (MRD) analysis in patients with various malignant diseases. Such diseases include childhood acute lymphoblastic leukemia, after induction therapy; acute promyelocytic leukemia, during and after chemotherapy; and chronic myelogenous leukemia, during treatment with alpha-interferon and after allogeneic bone marrow transplantation. Evaluation of the predictive value of the detection of MRD has to take into account its evolution and course, the pathogenesis, biology, and natural course of the underlying malignant disease, the molecular genetic lesion, and finally, the type of treatment. Quantification of minimal residual cells by the recently developed real-time quantitative PCR technique will surely have a major impact on our therapeutic strategies for patients with leukemia, lymphomas, and solid tumors. Based on quantitative PCR data, the terms molecular remission and molecular relapse have to be exactly defined and validated in prospective clinical trials to assess the biological and clinical significance of MRD in various types of malignancies.

Comparison of chromosome banding analysis, interphase- and hypermetaphase-FISH, qualitative and quantitative PCR for diagnosis and for follow-up in chronic myeloid leukemia: a study on 350 cases

For the diagnosis of CML and for monitoring of treatment response the detection of the t(9;22)(q34;q11) or the BCR-ABL rearrangement is necessary. Chromosome banding analysis (CA) is still the gold standard but other techniques like Southern blot, fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) are available. We analyzed 350 CML patients at different stages of disease in parallel with CA, interphase-FISH (IP-FISH), hypermetaphase-FISH (HM-FISH) and RT-PCR. In 20 cases with no Ph(+) metaphases in CA, HM-FISH detected 0.2 to 10% BCR-ABL(+)metaphases. After IP-FISH 107 samples were judged as negative. However, in 17 of these samples HM-FISH detected BCR-ABL(+) metaphases (0.3-11%), and in eight cases CA detected Ph(+) metaphases (2.5-25%). A comparison of IP-FISH performed on uncultivated cells vs cells cultivated for 48 h in 70 cases revealed a higher proportion of BCR-ABL+ cells in the cultivated samples. If nested PCR was negative, all other methods were negative in all cases too. In addition, 94 cases were evaluated using real-time PCR (LightCycler technology). The BCR-ABL/cABL ratio measured showed a high correlation with all other methods. Interestingly, a wide range in the BCR-ABL/ABL ratio was observed especially in patients who showed 100% Ph-positive metaphases in CA. In conclusion, CA, IP-FISH, HM-FISH and real-time PCR give reliable results but differences due to measurement of different target structures have to be kept in mind when using these data for definition of remission status.