New definition of remission in childhood acute lymphoblastic leukemia

IKZF1PLUS alterations contribute to outcome disparities in Hispanic/Latino children with B-lymphoblastic leukemia

BACKGROUND

Compared to other ethnicities, Hispanics/Latinos (H/L) have a high incidence of acute lymphoblastic leukemia (ALL), enrichment of unfavorable ALL genetic subtypes, and worse outcomes, even after correcting for socioeconomic factors. We previously demonstrated increased incidence of the high-risk genetic drivers IKZF1 deletion and IGH::CRLF2 rearrangement in H/L compared to non-H/L children with B-ALL. Here in an expanded pediatric cohort, we sought to identify novel genetic drivers and secondary genetic alterations in B-ALL associated with H/L ethnicity.

PROCEDURE

Comprehensive clinicopathologic data from patients with B-ALL treated from 2016 to 2020 were analyzed. Subtype was determined from karyotype, fluorescence in situ hybridization (FISH), chromosome microarray (CMA), and our next-generation sequencing (NGS) panel (OncoKids). Non-driver genetic variants were also examined. p-Values less than .05 (Fisher's exact test) were considered significant.

RESULTS

Among patients with B-ALL at diagnosis (n = 273), H/L patients (189, 69.2%) were older (p = .018), more likely to present with CNS2 or CNS3 disease (p = .004), and NCI high-risk ALL (p = .014) compared to non-H/L patients. Higher incidence of IGH::CRLF2 rearrangement (B-ALL, BCR::ABL1-like, unfavorable; p = .016) and lower incidence of ETV6::RUNX1 rearrangement (favorable, p = .02) were also associated with H/L ethnicity. Among secondary (non-subtype-defining) genetic variants, B-ALL in H/L was associated with IKFZ1 deletion alone (p = .001) or with IGH::CRLF2 rearrangement (p = .003). The IKZF1PLUS profile (IKZF1 deletion plus CDKN2A/2Bdel, PAX5del, or P2RY8::CRLF2 rearrangement without DUX4 rearrangement) was identified as a novel high-risk feature enriched in H/L patients (p = .001).

CONCLUSIONS

Our study shows enrichment of high-risk genetic variants in H/L B-ALL and raises consideration for novel therapeutic targets.

Circulating Tumor DNA in Pediatric Cancer

The measurement of circulating tumor DNA (ctDNA) has gained increasing prominence as a minimally invasive tool for the detection of cancer-specific markers in plasma. In adult cancers, ctDNA detection has shown value for disease-monitoring applications including tumor mutation profiling, risk stratification, relapse prediction, and treatment response evaluation. To date, there are ctDNA tests used as companion diagnostics for adult cancers and it is not understood why the same cannot be said about childhood cancer, despite the marked differences between adult and pediatric oncology. In this review, we discuss the current understanding of ctDNA as a disease monitoring biomarker in the context of pediatric malignancies, including the challenges associated with ctDNA detection in liquid biopsies. The data and conclusions from pediatric cancer studies of ctDNA are summarized, highlighting treatment response, disease monitoring and the detection of subclonal disease as applications of ctDNA. While the data from retrospective studies highlight the potential of ctDNA, large clinical trials are required for ctDNA analysis for routine clinical use in pediatric cancers. We outline the requirements for the standardization of ctDNA detection in pediatric cancers, including sample handling and reproducibility of results. With better understanding of the advantages and limitations of ctDNA and improved detection methods, ctDNA analysis may become the standard of care for patient monitoring in childhood cancers.

Early T-Cell Precursor ALL and Beyond: Immature and Ambiguous Lineage T-ALL Subsets

Simple Summary

Immature T-cell acute lymphoblastic leukemias englobes a wide range of low prevalence subtypes, not well identified, that in some cases overlap with myeloid lineage subtypes. Globally, this “grey zone” of immature leukemias, are difficult to precisely diagnose using a classical immunophenotypic approach. Interesting, genomic data collected during last years has shown that these subtypes share several genomic alterations, raising the question of how their phenotypes reflect distinct AL entities. Here we provide a systematic overview of the genetic events associated with immature T-ALL and outline their relationship with treatment choices and outcomes. Our goal is to offer a basis for using the genetic information for new diagnostic algorithms. An immunogenetic classification of these immature subtypes will better stratify patients and improve their management with more efficient and personalized therapeutic options.

Abstract

A wide range of immature acute leukemias (AL), ranging from acute myeloid leukemias with minimal differentiation to acute leukemias with an ambiguous lineage, i.e., acute undifferentiated leukemias and mixed phenotype acute leukemia with T- or B-plus myeloid markers, cannot be definitely assigned to a single cell lineage. This somewhat “grey zone” of AL expresses partly overlapping features with the most immature forms of T-cell acute lymphoblastic leukemia (T-ALL), i.e., early T-cell precursor ALL (ETP-ALL), near-ETP-ALL, and pro-T ALL. These are troublesome cases in terms of precise diagnosis because of their similarities and overlapping phenotypic features. Moreover, it has become evident that they share several genomic alterations, raising the question of how their phenotypes reflect distinct AL entities. The aim of this review was to provide a systematic overview of the genetic events associated with immature T-ALL and outline their relationship with treatment choices and outcomes, especially looking at the most recent preclinical and clinical studies. We wish to offer a basis for using the genetic information for new diagnostic algorithms, in order to better stratify patients and improve their management with more efficient and personalized therapeutic options. Understanding the genetic profile of this high-risk T-ALL subset is a prerequisite for changing the current clinical scenario.

Remission, treatment failure, and relapse in pediatric ALL: an international consensus of the Ponte-di-Legno Consortium

Comparison of treatment strategies in de novo pediatric acute lymphoblastic leukemia (ALL) requires standardized measures of efficacy. Key parameters that define disease-related events, including complete remission (CR), treatment failure (TF; not achieving CR), and relapse (loss of CR) require an updated consensus incorporating modern diagnostics. We collected the definitions of CR, TF, and relapse from recent and current pediatric clinical trials for the treatment of ALL, including the key components of response evaluation (timing, anatomic sites, detection methods, and thresholds) and found significant heterogeneity, most notably in the definition of TF. Representatives of the major international ALL clinical trial groups convened to establish consensus definitions. CR should be defined at a time point no earlier than at the end of induction and should include the reduction of blasts below a specific threshold in bone marrow and extramedullary sites, incorporating minimal residual disease (MRD) techniques for marrow evaluations. TF should be defined as failure to achieve CR by a prespecified time point in therapy. Relapse can only be defined in patients who have achieved CR and must include a specific threshold of leukemic cells in the bone marrow confirmed by MRD, the detection of central nervous system leukemia, or documentation of extramedullary disease. Definitions of TF and relapse should harmonize with eligibility criteria for clinical trials in relapsed/refractory ALL. These consensus definitions will enhance the ability to compare outcomes across pediatric ALL trials and facilitate development of future international collaborative trials.

Significance of NOTCH1 mutations détections in T-acute lymphoblastic leukemia patients

BACKGROUND

This study aimed to determine the prevalence and clinical impact of neurogenic locus notch homolog protein 1 (NOTCH1) mutations among patients with T cell acute lymphoblastic leukemia (T-ALL).

PATIENT AND METHODS

A cohort of 60 T-ALL cases was included in this study. Sanger sequencing were done for NOTCH1 exon 26, 27, and distal part of exon 34 expanding the sequences encoding transcription activation domain (TAD) and a peptide sequence rich in proline, glutamic acid, serine, threonine (PEST) domains in all studied T ALL patients at diagnosis.

RESULTS

NOTCH1 mutations was detected in 40 out of 60 T-ALL patients (66%). Mutations in T-ALL patients are deletions (22 mutations) and point mutation (10 mutations). NOTCH1 mutations was found to have no significant impact on clinical outcome and prognosis in T-ALL including overall survival, progression free survival, relapse and mortality (P> 0.05 for all).

CONCLUSION

NOTCH1 mutations were frequently detected in T All patients; however, these mutations did not affect the T ALL patient's outcome. The high prevalence of NOTCH1 mutations at diagnosis could be used for detection of minimal residual disease in T ALL.

Clinical value of the quantitation of average daily platelet increase during the recovery period in childhood acute lymphoblastic leukaemia

The time to platelet recovery (TPR) is becoming a predicting factor during the treatment of childhood acute leukaemia. However, the initial pre-treatment platelet count (PPC) could interfere with TPR. Here, we integrated both TPR and PPC as the average daily platelet amount increase (Ap) to predict the prognosis in childhood B-ALL during the recovery period.148 patients were enrolled. The relationship between the Ap and MRD was evaluated, and Multivariate analysis was performed to evaluate whether Ap was independently associated with a better EFS. The PPC was inversely correlated with TPR (rs = -0.519, P = 0.021). Patients in Ap >3.9 × 10⁹/L group had better EFS (x² = 3.109, P = 0.028) than TPR ≤ 16d. Multivariate analysis indicated that Ap > 3.9 × 10⁹/L was independently associated with a longer EFS (RR = 3.468; 95%CI: 1.037-11.597, P = 0.043). However, when introducing both MRD and Ap > 3.9 × 10⁹/L as candidate variables, the Ap > 3.9 × 10⁹/L lost its independent effect (P = 0.081). The strong association between MRD on treatment day 33 and Ap > 3.9 × 10⁹/L (x² = 148.00, P = 0.000) was responsible for this phenomenon. Ap could be a valuable prognostic indicator in childhood B-ALL.

Pretransplant Consolidation Is Not Beneficial for Adults with ALL Undergoing Myeloablative Allogeneic Transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) is curative for patients with acute lymphoblastic leukemia (ALL) who achieve complete remission (CR1) with chemotherapy. However, the benefit of consolidation chemotherapy remains uncertain in patients undergoing alloHCT. We compared clinical outcomes of 524 adult patients with ALL in CR1 who received ≥2 (n = 109), 1 (n = 93), or 0 cycles (n = 322) of consolidation before myeloablative alloHCT from 2008 to 2012. As expected, time to alloHCT was longer with increasing cycles of consolidation. Patients receiving ≥2, 1, or 0 cycles of consolidation had an adjusted 3-year cumulative incidence of relapse of 20%, 27%, and 22%; 1-year transplant-related mortality (TRM) of 16%, 18%, and 23%; adjusted 3-year leukemia-free survival (LFS) of 54%, 48%, and 47%; and 3-year overall survival (OS) of 63%, 59%, and 54% (all P values >.40). Multivariable analysis confirmed that consolidation was not prognostic for LFS (relative risk, 1.20, 95% confidence interval, .86 to 1.67; P = .28 for no consolidation; RR, 1.18, 95% confidence interval, .79 to 1.76; P = .41 for 1 cycle versus ≥2 cycles = reference). Similarly, consolidation was not associated with OS, relapse, TRM, or graft-versus-host disease. We conclude that consolidation chemotherapy does not appear to provide added benefit in adult ALL patients with available donors who undergo myeloablative alloHCT in CR1.

An update on PCR use for minimal residual disease monitoring in acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is the first neoplasm where the assessment of early response to therapy by minimal residual disease (MRD) monitoring has proven to be a fundamental tool for guiding therapeutic choices. In recent years, thanks to real-time quantitative PCR (qPCR), MRD monitoring has further achieved higher levels of sensitivity and standardization. However, some outstanding issues still remain to be addressed and emerging technologies hold the promise of improving MRD detection in ALL patients. Areas covered: Through a comprehensive review of the literature, we analyze the state-of-the-art of molecular MRD assessment in ALL to better understand how, in the upcoming years, some of its limitations could be tackled by emerging molecular technologies. Furthermore, we highlight the future role of molecular MRD monitoring in the context of personalized protocols, taking into account the growing genetic complexity in ALL. Expert commentary: Although new molecular technologies are promising tools for MRD assessment, qPCR still remains the gold standard for evaluating MRD in ALL. High-throughput sequencing and droplet digital PCR allow to identify new prognostic factors and/or MRD targets at diagnosis and to perform earlier MRD evaluations, thereby optimizing patient stratification and earlier MRD-based clinical intervention to improve ALL patient outcomes.

Redefining treatment failure for pediatric acute leukemia in the era of minimal residual disease testing

Technologies for the detection of minimal residual disease (MRD) in leukemia and our understanding of the prognostic implications of MRD at different phases of treatment have significantly improved over the past decade. As a result, definitions of treatment failure based on bone marrow morphology by light microscopy are becoming increasingly inadequate for clinical care and trial design. In addition, novel therapies that may have increased efficacy and decreased toxicity in the setting of MRD compared to overt disease are changing clinical practice and challenging investigators to redefine treatment failure, the role of disease surveillance in remission, and clinical trial eligibility in the era of MRD.

Lorenz system in the thermodynamic modelling of leukaemia malignancy

The core idea of the proposed thermodynamic modelling of malignancy in leukaemia is entropy arising within normal haematopoiesis. Mathematically its description is supposed to be similar to the Lorenz system of ordinary differential equations for simplified processes of heat flow in fluids. The hypothetical model provides a description of remission and relapse in leukaemia as two hierarchical and qualitatively different states of normal haematopoiesis with their own phase spaces. Phase space transition is possible through pitchfork bifurcation, which is considered the common symmetrical scenario for relapse, induced remission and the spontaneous remission of leukaemia. Cytopenia is regarded as an adaptive reaction of haematopoiesis to an increase in entropy caused by leukaemia clones. The following predictions are formulated: a) the percentage of leukaemia cells in marrow as a criterion of remission or relapse is not necessarily constant but is a variable value; b) the probability of remission depends upon normal haematopoiesis reaching bifurcation; c) the duration of remission depends upon the eradication of leukaemia cells through induction or consolidation therapies; d) excessively high doses of chemotherapy in consolidation may induce relapse.

Significance of CD99 expression in T-lineage acute lymphoblastic leukemia

BACKGROUND

CD99 was first isolated as an antigen on the T acute lymphoblastic leukemia cells. It has been shown to participate in T cell adhesion and is widely expressed on a variety of hematopoietic and non-hematopoietic cell types.

AIM OF WORK

Detection of the expression pattern of CD99 on leukemic and normal T cells and assessing the possibility of its use as a tool for the diagnosis and monitoring of T-ALL cases.

METHODOLOGY

We used flow cytometry technique to determine the expression level of CD99 in 62 newly diagnosed T-ALL patients. Patients were followed up for the presence of minimal residual disease on day 15 and day 42 post-therapy. 20 age and sex matched healthy controls were enrolled in our study.

RESULTS

CD99 was expressed in all T-ALL patients, with a higher median expression level when compared to controls (58.5% versus 1.38%, p< 0.001). On day 42 post-therapy, 100% of follow up patients who had initial CD99 expression ≤ 50% had no minimal residual disease, while only 45.5% of those who had initial CD99 expression > 50% had no minimal residual disease (P= 0.03). There was no significant influence of CD99 expression on the 1-year overall survival probability (P= 0.82).

CONCLUSION

CD99 could be used to complement current strategy relying on TdT for diagnosis and monitoring of minimal residual disease during the post-therapy follow up of T-ALL patients. Further studies are needed to confirm these findings.

Understanding the Clinical Implications of Minimal Residual Disease in Childhood Leukemia

Improved laboratory techniques now allow a more sensitive detection of leukemia cells at designated intervals throughout therapy. Using flow cytometry and polymerase chain reaction, it is possible to detect 1 leukemic cell among 10 4 normal cells (1 leukemia cell in 10,000 normal cells), representing a 100-fold greater sensitivity than morphological examination in acute lymphoblastic leukemia (ALL). Recently, it has been shown that the molecular presence of persistent acute lymphoblastic leukemia at the end of remission therapy is a poor indicator of clinical outcome. Now similar studies are being performed in acute myeloid leukemia (AML). While the sensitivity using flow cytometry is less in AML than in ALL (able to detect 1 leukemic cell among 1000 normal cells in AML), persistent or minimal residual AML provides the clinician guidance with future treatment recommendations. Minimal residual disease (MRD) is now considered an important indicator response of disease response to treatment. As such, MRD once considered a research variable is now influencing treatment decisions. Therefore, it is imperative that the nurse have an understanding of the newer techniques to study residual leukemia and their clinical implications for patients and their families.

Minimal Residual Disease and Childhood Leukemia: Standard of Care Recommendations From the Pediatric Oncology Group of Ontario MRD Working Group

Minimal residual disease (MRD) is an independent predictor of relapse risk in children with leukemia and is widely used for risk-adapted treatment. This article summarizes current evidence supporting the use of MRD, including clinical significance, current international clinical practice, impact statement, and recommended indications. The proposed MRD recommendations have been endorsed by the MRD Working Group of the Pediatric Oncology Group of Ontario and provide the foundation for a strategy that aims at equitable access to MRD evaluation for children with leukemia.

Aberrations in DNA methylation are detectable during remission of acute lymphoblastic leukemia and predict patient outcome

AIM

Aberrant DNA methylation patterns are a hallmark of cancer, although the extent to which they underlie cancer development is unknown. In this study, we aimed to determine whether acute lymphoblastic leukemia (ALL) patients in clinical remission retained abnormal DNA methylation patters and whether these were associated with patient outcome.

MATERIALS & METHODS

We investigated CpG island methylation of genes known to exhibit hypermethylation in leukemia using quantitative pyrosequencing analysis.

RESULTS

Although methylation levels were reduced in remission samples, they remained significantly higher than those seen in healthy controls. This retained methylation was not related to low levels of residual leukemia cells still present at remission. Methylation levels were also stable (or increased) during continuous remission and significantly correlated with long-term survival in adult ALL patients.

CONCLUSION

This study determined that abnormalities in DNA methylation are retained during ALL remission and may represent a novel prognostic marker for adult ALL patients.

Risk factors for relapse in childhood acute lymphoblastic leukemia: prediction and prevention

With current treatment regimens, survival rates for acute lymphoblastic leukemia (ALL) have improved dramatically since the 1980s, with current 5-year overall survival rates estimated at greater than 85%. This success was achieved, in part, through the implementation of risk-stratified therapy. Nevertheless, for a subgroup of patients (15-20%) with newly diagnosed ALL who will ultimately relapse, traditional risk assessment remains inadequate. The risk of relapse may be estimated on the basis of diagnostic features or early treatment response findings. Further progress in this field may thus come from refinement of predictive factors for relapse and treatment adaptation and from the identification of biological subsets of ALL patients who could benefit from specific target therapies. This article summarizes the aspects associated with the identification of predictive factors for relapse in childhood ALL and options available for prevention of disease recurrence.

Postinduction minimal residual disease monitoring by polymerase chain reaction in children with acute lymphoblastic leukemia

PURPOSE

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. Monitoring minimal residual disease (MRD) by using real-time quantitative polymerase chain reaction (RQ-PCR) provides information for patient stratification and individual risk-directed treatment. Cooperative studies have documented that measurement of blast clearance from the bone marrow during and after induction therapy identifies patient populations with different risk of relapse. We explored the possible contribution of measurements of MRD during the course of treatment.

PATIENTS AND METHODS

We used RQ-PCR to detect MRD in 110 unselected patients treated in Italy in the International Collaborative Treatment Protocol for Children and Adolescents With Acute Lymphoblastic Leukemia (AIEOP-BFM ALL 2000). The trial took place in AIEOP centers during postinduction chemotherapy. Results were categorized as negative, low positive (below the quantitative range [< 5 × 10(-4)]), or high positive (≥ 5 × 10(-4)). Patients with at least one low-positive or high-positive result were assigned to the corresponding subgroup.

RESULTS

Patients who tested high positive, low positive, or negative had significantly different cumulative incidences of leukemia relapse: 83.3%, 34.8%, and 8.6%, respectively (P < .001). Two thirds of positive cases were identified within 4 months after induction-consolidation therapy, suggesting that this time frame may be most suitable for cost-effective MRD monitoring, particularly in patients who did not clear their disease at the end of consolidation.

CONCLUSION

These findings provide further insights into the dynamic of MRD and the ongoing effort to define molecular relapse in childhood ALL.

Fenretinide cytotoxicity is independent of both constitutive and pharmacologically modulated glutathione levels in pediatric acute lymphoblastic leukemia cells cultured at hypoxia

Fenretinide (4-HPR) cytotoxicity relative to glutathione levels in pediatric acute lymphoblastic leukemia cell lines cultured at bone marrow level hypoxia (5% O2) is evaluated. 4-HPR cytotoxicity correlated with reactive oxygen species generation (P < 0.001),but not with levels of intracellular glutathione, g-glutamylcysteine synthase, or glutathione peroxidase. Buthionine sulfoximine (BSO)reduced glutathione levels in 10 cell lines (P < 0.001), but 4-HPR þ BSO was markedly synergistic in only 1 of 10 lines. Pretreatment with N-acetylcysteine increased glutathione (P < 0.02)but did not alter 4-HPR cytotoxicity. Our data suggest that 4-HPR cytotoxicity is independent of glutathione under physiologic oxygen tension.

Bone marrow aspiration technique may have an impact on therapy stratification in children with acute lymphoblastic leukaemia

BACKGROUND

Morphological evaluation of early response to chemotherapy and measurement of minimal residual disease by flow cytometry or PCR are being used for evaluation of prognosis and treatment stratification in children with acute lymphoblastic leukaemia (ALL).

PROCEDURE

In a series of 14 consecutive bone marrow investigations from children with precursor B-cell ALL, morphological evaluations of smears and flow cytometric measurements of minimal residual disease in sequentially aspirated small (2 ml) and large (5-10 ml) volumes of bone marrow were compared, at various time points during therapy.

RESULTS

The density of nucleated cells was markedly reduced in the large volume aspirate. The percentage of erythroblasts measured by flow cytometry was smaller, indicating dilution with peripheral cells. Similarly, the blast percentage was reduced with 54% in large aspirates, and in four instances with minimal residual disease of >0.1% in the small volume, the level of blasts in the large aspirate was below this limit.

CONCLUSIONS

The amount of minimal residual disease should be measured in the first 2.5 ml of bone marrow aspirated from one puncture site. The procedure should be performed by experienced and carefully instructed doctors. In large aspirates, minimal residual disease will be underestimated, which may lead to failure to undertake a required intensification of therapy and a lower fraction of high risk patients in the trial.

Prognostic significance of minimal residual disease detected by a simplified flow cytometric assay during remission induction chemotherapy in children with acute lymphoblastic leukemia

Purpose

Our study attempted to determine the prognostic significance of minimal residual disease (MRD) detected by a simplified flow cytometric assay during induction chemotherapy in children with B-cell acute lymphoblastic leukemia (B-ALL).

Methods

A total of 98 patients were newly diagnosed with precursor B-ALL from June 2004 to December 2008 at the Asan Medical Center (Seoul, Korea). Of those, 37 were eligible for flow cytometric MRD study analysis on day 14 of their induction treatment. The flow cytometric MRD assay was based on the expression intensity of CD19/CD10/CD34 or aberrant expression of myeloid antigens by bone marrow nucleated cells.

Results

Thirty-five patients (94.6%) had CD19-positive leukemic cells that also expressed CD10 and/or CD34, and 18 (48.6%) had leukemic cells with aberrant expression of myeloid antigens. Seven patients with ≥1% leukemic cells on day 14 had a significantly lower relapse-free survival (RFS) compared to the 30 patients with lower levels (42.9% [18.7%] vs. 92.0% [5.4%], P=0.004). Stratification into 3 MRD groups (≥1%, 0.1-1%, and <0.1%) also showed a statistically significant difference in RFS (42.9% [18.7%] vs. 86.9% [8.7%] vs. 100%, P=0.013). However, the MRD status had no significant influence on overall survival. Multivariate analysis demonstrated that the MRD level on day 14 was an independent prognostic factor with borderline significance.

Conclusion

An MRD assay using simplified flow cytometry during induction chemotherapy may help to identify patients with B-ALL who have an excellent outcome and patients who are at higher risk for relapse.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: report from the Committee on Disease-Specific Methods and Strategies for Monitoring Relapse following Allogeneic Stem Cell Transplantation. Part I: Methods, acute leukemias, and myelodysplastic syndromes

Relapse has become the major cause of treatment failure after allogeneic stem cell transplantation. Outcome of patients with clinical relapse after transplantation generally remains poor, but intervention prior to florid relapse improves outcome for certain hematologic malignancies. To detect early relapse or minimal residual disease, sensitive methods such as molecular genetics, tumor-specific molecular primers, fluorescein in situ hybridization, and multiparameter flow cytometry (MFC) are commonly used after allogeneic stem cell transplantation to monitor patients, but not all of them are included in the commonly employed disease-specific response criteria. The highest sensitivity and specificity can be achieved by molecular monitoring of tumor- or patient-specific markers measured by polymerase chain reaction-based techniques, but not all diseases have such targets for monitoring. Similar high sensitivity can be achieved by determination of donor chimerism, but its specificity regarding detection of relapse is low and differs substantially among diseases. Here, we summarize the current knowledge about the utilization of such sensitive monitoring techniques based on tumor-specific markers and donor cell chimerism and how these methods might augment the standard definitions of posttransplant remission, persistence, progression, relapse, and the prediction of relapse. Critically important is the need for standardization of the different residual disease techniques and to assess the clinical relevance of minimal residual disease and chimerism surveillance in individual diseases, which in turn, must be followed by studies to assess the potential impact of specific interventional strategies.

Risk-adapted treatment of pediatric acute lymphoblastic leukemia

Optimal use of antileukemic agents and stringent application of risk-directed therapy in clinical trials have resulted in steady improvement in the outcome of children with acute lymphoblastic leukemia, with current cure rates exceeding 80% in developed countries. The intensity of treatment varies substantially among subsets of patients, as therapy is designed to reduce acute and long-term toxicity in low-risk groups while improving outcomes in poor risk groups by treatment intensification. Recent advances in genome-wide screening techniques, pharmacogenomic studies, and development of molecular therapeutics are ushering in an era of more refined personalized therapy.

Detection of early precursors of t(12;21) positive pediatric acute lymphoblastic leukemia during follow-up

DNA-, RNA-, and cell-based methods provide different biologic information for determining the presence of minimal residual disease (MRD). We monitored the responses of patients with pediatric acute lymphoblastic leukemia (pALL) using DNA markers, TEL/AML1 expression, and scanning fluorescence microscopy (SFM). Using SFM, 36% of patients exhibited 1.5-3.1 log and 2.9-4.2 log higher MRD levels compared with those based on DNA and RNA markers, respectively. CD10+ ancestor cells with germline antigen receptors, but silent TEL/AML1 expression, may reside in the lymphoid stem cell compartment of treated t(12;21)-positive patients and might act as a potential source of cells for late relapses.

How and why minimal residual disease studies are necessary in leukemia: a review from WP10 and WP12 of the European LeukaemiaNet

Resistance to therapeutic agents is a major factor in the failure of cancer treatments. In leukemia, the resistant cells remaining in the bone marrow and/or peripheral blood constitute minimal residual disease and are detectable by highly sensitive assays when the patient appears to be in complete remission. Early detection of the expansion of residual cells permits clinical intervention with the aim of reversing the proliferation of resistant leukemic cells. Therefore, accurate and precise measurement of minimal residual disease can greatly enhance optimization of oncology patients' clinical management. This notion is supported by a large body of data among chronic myeloid leukemia patients, but minimal residual disease detection and monitoring is increasingly applied to other types of leukemia, and is starting to be a factor in decision-making for some therapeutic trials in childhood acute lymphoblastic leukemia. Here, from the solid ground of minimal residual disease detection in chronic myeloid leukemia, the current state of the art and development of molecular techniques in other leukemias and the growing field of multiparameter flow cytometry are reviewed in two separate parts reporting on the respective advances, advantages and pitfalls of these emerging methods.

The role of multiparameter flow cytometry for detection of minimal residual disease in acute myeloid leukemia

The presence of minimal residual disease (MRD) in the bone marrow (BM) of patients with acute myeloid leukemia (AML) following chemotherapy has been established by many studies to be strongly associated with relapse of leukemia. In addition, detection of MRD is the major objective of many of the newer diagnostic techniques used in malignant hematology. Because of the wide availability and conceptual straightforwardness of immunophenotyping, flow cytometry is the most accessible method for MRD detection. This review is not an overview of all MRD studies, but rather discusses the possibilities for optimizing MRD detection, the use of multiparameter flow cytometry (MFC) techniques in MRD detection, and the implications for future patient treatment. This review focuses on MRD detection in AML using MFC and discusses the reported correlations of MRD, clinical and biologic features of the disease, and outcome. In addition, it discusses the laboratory and clinical aspects of this approach.

Prognostic factors for leukemic induction failure in children with acute lymphoblastic leukemia and outcome after salvage therapy: the FRALLE 93 study

PURPOSE

To identify prognostic factors and to evaluate the outcome of children with acute lymphoblastic leukemia (ALL) failure after induction therapy.

PATIENTS AND METHODS

Between June 1993 and December 1999, 1,395 leukemic children were included in the French Acute Lymphoblastic Leukemia 93 study.

RESULTS

Fifty-three patients (3.8%) had a leukemic induction failure (LIF) after three- or four-drug induction therapy. In univariate analysis, high WBC count (P = .001), mediastinal mass (P = .017), T-cell phenotype (T-ALL; P = .001), t(9;22) translocation (P = .001), and a slow early response (at day 8 and/or on day 21, P = .001) were predictive of LIF. The following three prognostic groups for LIF were identified by multivariate analysis: a low-risk group with B-cell progenitor (BCP) ALL without t(9;22) (odds ratio [OR] = 1), an intermediate-risk group with T-ALL and a mediastinal mass (OR = 7.4, P < .0001), and a high-risk group with BCP-ALL and t(9;22) or T-ALL without a mediastinal mass (OR = 28.4, P < .0001). Complete remission (CR) was subsequently obtained in 43 patients (81%). The 5-year overall survival (OS) rate of the 53 patients was 30% +/- 6%. The 5-year OS rate among allogeneic graft recipients, autologous graft recipients, and after chemotherapy were 30.4% +/- 9.6% (50% +/- 26% after genoidentical transplantation), 50% +/- 17.7%, and 41.7% +/- 14.2%, respectively (P = .18). Fourteen patients (26%) were still in first CR after a median of 83 months (range, 53 to 117 months).

CONCLUSION

Three risk categories for LIF in children with ALL were identified. Approximately one third of patients with LIF can be successfully treated with salvage therapy overall. Subsequent CR after LIF is mandatory for cure.

Prognostic role of minimal residual disease in mature B-cell acute lymphoblastic leukemia of childhood

PURPOSE

To study the prevalence of t(8;14) at diagnosis and the response kinetics to treatment of minimal residual disease (MRD) in B-cell acute lymphoblastic leukemia (B-ALL) patients and determine its impact on prognosis.

PATIENTS AND METHODS

A total of 68 children affected by de novo B-ALL enrolled onto the Berlin-Frankfurt-Muenster-based Italian Association of Pediatric Hematology and Oncology LNH-97 clinical protocol were studied. Bone marrow aspirate from each patient was analyzed for the presence of t(8;14)(q24;q32) by long-distance polymerase chain reaction at diagnosis, after the first chemotherapy cycle, and after subsequent cycles until negative for MRD. Morphologic and immunophenotypic analyses were reviewed centrally.

RESULTS

A total of 47 patients (69%) were positive for t(8;14)(q24;q32). MRD response kinetics was determined in 39 patients. All of them reached clinical complete remission and most (31 of 39) became MRD negative after the first chemotherapy cycle. The 3-year relapse-free survival (RFS) was 38% (SE = 17%) in patients MRD positive after the first chemotherapy cycle compared with 84% (SE = 7%) in MRD-negative patients (P = .0005), whereas there was no difference in RFS for children who reached a clinical complete remission after the first chemotherapy cycle versus those who did not (RFS = 72% and SE = 9%; RFS = 79% and SE = 11%, respectively; P = .8). In multivariate analysis, MRD was shown to be predictive of higher risk of failure.

CONCLUSION

Our study demonstrated that MRD carries a negative prognostic impact in B-ALL patients and suggests that a better risk-adapted therapy, possibly including the use of anti-CD20 monoclonal antibody, should be considered in selected patients.

Comparison of minimal residual disease (MRD) estimated by flow cytometry and by real-time quantitative PCR of Wilms tumor gene 1 (WT1) transcript expression in children with acute lymphoblastic leukemia

Minimal residual disease (MRD) in 56 children with acute lymphoblastic leukemia (ALL) was quantified simultaneously by flow cytometry and by RQ-PCR of WT1 transcripts. Six patients failed remission induction, all had detectable MRD by flow cytometry, and two had undetectable MRD by WT1 assay. Among 41 patients, who achieved remission and had overexpression of WT1 transcripts at diagnosis, the two techniques gave concordant MRD results in 26 and discordant MRD results in 15. Nine patients did not show overexpression of WT1 at diagnosis. Our results indicate that RQ-PCR measurements of WT1 may be of limited value for monitoring MRD in childhood ALL.

Quantitative analysis of minimal residual disease predicts relapse in children with B-lineage acute lymphoblastic leukemia in DFCI ALL Consortium Protocol 95-01

In a prospective trial in 284 children with B-lineage acute lymphoblastic leukemia (ALL), we assessed the clinical utility of real-time quantitative polymerase chain reaction analysis of antigen receptor gene rearrangements for detection of minimal residual disease (MRD) to identify children at high risk of relapse. At the end of induction therapy, the 5-year risk of relapse was 5% in 176 children with no detectable MRD and 44% in 108 children with detectable MRD (P < .001), with a linear association of the level of MRD and subsequent relapse. Recursive partitioning and clinical characteristics identified that the optimal cutoff level of MRD to predict outcome was 10(-3). The 5-year risk of relapse was 12% for children with MRD less than one leukemia cell per 10(3) normal cells (low MRD) but 72% for children with MRD levels greater than this level (high MRD) (P < .001) and children with high MRD had a 10.5-fold greater risk of relapse. Based upon these results we have altered our treatment regimen for children with B-lineage ALL and children with MRD levels greater than or equal to 10(-3) at the end of 4 weeks of multiagent induction chemotherapy now receive intensified treatment to attempt to decrease their risk of subsequent relapse.

Diagnostic pathways in acute leukemias: a proposal for a multimodal approach

Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) each represent a heterogeneous complex of disorders, which result from diverse mechanisms of leukemogenesis. Modern therapeutic concepts are based on individual risk stratification at diagnosis and during follow-up. For some leukemia subtypes such as AML M3/M3v with t(15;17)/PML-RARA or Philadelphia-positive ALL targeted therapy options are available. Thus, optimal therapeutic conditions are based on exact classification of the acute leukemia subtype at diagnosis and are guided by exact and sensitive quantification of minimal residual disease during complete hematologic remission. Today, a multimodal diagnostic approach combining cytomorphology, multiparameter flow cytometry, chromosome banding analysis, accompanied by diverse fluorescence in situ hybridization techniques, and molecular analyses is needed to meet these requirements. As the diagnostic process becomes more demanding with respect to experience of personnel, time, and costs due to the expansion of methods, algorithms, which guide the diagnostic procedure from basic to more specific methods and which lead finally to a synopsis of the respective results, are essential for modern diagnostics and therapeutic concepts.

Analysis of minimal residual disease by Ig/TCR gene rearrangements: guidelines for interpretation of real-time quantitative PCR data

Most modern treatment protocols for acute lymphoblastic leukaemia (ALL) include the analysis of minimal residual disease (MRD). To ensure comparable MRD results between different MRD-polymerase chain reaction (PCR) laboratories, standardization and quality control are essential. The European Study Group on MRD detection in ALL (ESG-MRD-ALL), consisting of 30 MRD-PCR laboratories worldwide, has developed guidelines for the interpretation of real-time quantitative PCR-based MRD data. The application of these guidelines ensures identical interpretation of MRD data between different laboratories of the same MRD-based clinical protocol. Furthermore, the ESG-MRD-ALL guidelines will facilitate the comparison of MRD data obtained in different treatment protocols, including those with new drugs.

Automated detection of residual leukemic cells by consecutive immunolabeling for CD10 and fluorescence in situ hybridization for ETV6/RUNX1 rearrangement in childhood acute lymphoblastic leukemia

Among the various methods available for analyzing minimal residual disease, a new procedure for the cell-based approaches using consecutive phenotypic and genotypic analysis as revealed by immunofluorescent labeling and subsequent fluorescent in situ hybridization (FISH) has been developed. We are introducing a fluorescent microscopy-based technique by which not only cellular targets and immunological marker positivity, but also the FISH pattern was identified by automated scanning. For the latter one translocation-specific FISH pattern recognition was accomplished by using an automated scanning mode for the 3D determination of valid distances between FISH signals, to define the cutoff value for the shortest green-red spot distance differentiating positive cells from negative ones. The procedure was tested with CD10(+) acute lymphoblastic leukemia cell line harboring the t(12;21)(p13;q22) resulting in the ETV6/RUNX1 rearrangement (formerly TEL/AML1), as well as peripheral blood lymphocytes of healthy individuals. Using the combined, automated method, a sensitivity of 98.67% and a specificity of 99.97% were obtained. The mean false positivity + 2 standard deviations cutoff level (0.09%) allows detection of leukemic cells with high accuracy, even a bit below the tumor load dilution of 10(-3), a value reported to be critical in clinical decision making.

[Minimal residual disease in acute lymphoblastic leukemia: a new concept of complete remission]

INTRODUCTION

Early response to induction treatment is one of the most important prognostic factors in children with acute lymphoblastic leukemia (ALL). Cytological remission is currently achieved in 95-98 % of these patients, although a significant proportion will later relapse. More sensitive techniques are required to measure residual leukemia and establish a new definition of complete remission.

OBJECTIVE

To identify minimal residual disease (MRD) by immunological techniques and define its prognostic impact in children with ALL.

METHODS

MRD was studied by flow cytometry in 53 children diagnosed in our department between June 1999 and April 2003 and treated using the Pethema protocols. All the children achieved complete cytological remission (< 5 %) with the induction treatment and had at least one useful phenotype for follow-up: 11 % were T phenotype, one was biphenotypic and the remainder were B cell leukemias. Bone marrow samples were analyzed post-induction, post-consolidation, after 6 and 11 months of maintenance treatment, at the end of treatment, and 3 months later. The positivity threshold was set at 0.01 % and the sensitivity of the technique was 1 x 10(-4)-1 x 10(-5).

RESULTS

A total of 199 samples were analyzed. Thirty-seven percent of the post-induction and 20 % of the post-consolidation samples analyzed were MRD-positive. Elimination was slower in patients with a T phenotype and in high-risk patients according to the traditional classification. After a median follow-up of 26 months, event free survival (EFS) in the group as a whole was 92 %. The EFS rate in the patients who were MRD-positive post-induction was 79 %. None of the patients who were MRD-negative post-induction has developed recurrence.

CONCLUSION

Study of MRD is essential and should be included in all current treatment protocols for children with ALL. Its usefulness derives from the prognostic impact of the response to induction treatment. Continued sequential monitoring may predict recurrence before the onset of clinical or hematologic manifestations.

Early response to induction is predictive of survival in childhood Philadelphia chromosome positive acute lymphoblastic leukaemia: results of the Medical Research Council ALL 97 trial

We report on the outcome of children with Philadelphia positive acute lymphoblastic leukaemia (Ph+ ALL) treated on the UK Medical Research Council (MRC) trial for childhood ALL, MRC ALL 97, between January 1997 and June 2002. Forty-two (2.3%) patients were Ph+. Nineteen (45%) had <25% blasts in bone marrow (BM) within the first 2 weeks of treatment and were defined as a good response group (GRG), the others as a poor response group (PRG). Thirty-six (86%) achieved first complete remission (CR1) at the end of induction, of which 28 underwent BM transplantation (BMT). The median follow-up was 42 months (range, 21-84). The 3-year event-free survival (EFS; 52%, 95% CI, 36-66%) was a considerable improvement on the previous MRC UKALL XI trial (27%). EFS for the GRG and PRG were 68% (43-84%) and 39% (18-59%), respectively (P = 0.03); presenting white cell count <50 x 10(9)/l (P = 0.02) was predictive for overall survival. Changes in the MRC ALL97 trial within the study period resulted in some Ph+ ALL receiving daunorubicin and either prednisolone or dexamethasone during induction. Though the use of daunorubicin during induction was not a prospective study question, EFS was significantly better for those whose induction included this drug (P = 0.02). Steroid randomization was not stratified for Ph+ ALL patients and was not predictive for EFS. BMT in CR1 appeared to reduce the risk of a subsequent BM relapse. These results show significant improvement on previous MRC trials; future therapeutic strategies should include early intensive therapy and BMT in CR1.

The seventh international childhood acute lymphoblastic leukemia workshop report: Palermo, Italy, January 29--30, 2005

Between 1995 and 2004, six International Childhood Acute Lymphoblastic Leukemia (ALL) Workshop have been held, and the completion of several collaborative projects has established the clinical relevance and treatment options for several specific genetic subtypes of ALL. This meeting report summarizes the data presented in the seventh meeting and the discussion.

Philadelphia positive acute lymphoblastic leukaemia of childhood

On current chemotherapeutic regimens, children with Philadelphia positive acute lymphoblastic leukaemia show a heterogeneous response to treatment. A few respond quickly to treatment and achieve long-term remission. Some fail to achieve remission after induction and the majority respond slowly to treatment. Relapse on treatment is common and remission is sustained in a proportion of cases only after allogeneic stem cell transplantation (allo-SCT). The use of imatinib along with conventional cytoreductive therapy, prior to allo-SCT appears to be the most promising strategy. The future lies in the molecular evaluation of response to treatment and combination targeted chemotherapy.

Concurrent detection of minimal residual disease (MRD) in childhood acute lymphoblastic leukaemia by flow cytometry and real-time PCR

Minimal (i.e. submicroscopic) residual disease (MRD) predicts outcome in childhood acute lymphoblastic leukaemia (ALL). To be used clinically, MRD assays must be reliable and accurate. Two well-established techniques, flow cytometry (FC) and polymerase chain reaction (PCR), can detect leukaemic cells with a sensitivity of 0.01% (10(-4)). We analysed diagnostic samples of 45 ALL-patients (37 B-lineage ALL, eight T-lineage ALL) by four-colour FC and real-time PCR. Leukaemia-associated immunophenotypes, at a sensitivity of MRD detection by FC at the 0.01% level, were identified in 41 cases (91%); antigen-receptor gene rearrangements suitable for MRD detection with a sensitivity of 0.01% or better by PCR were identified in 38 cases (84%). The combined use of FC and PCR allowed MRD monitoring in all 45 patients. In 105 follow-up samples, MRD estimates by both methods were highly concordant, with a deviation factor of <5 by Bland-Altman analysis. Importantly, the concordance between FC and PCR was also observed in regenerating bone marrow samples containing high proportions of CD19(+) cells, and in samples studied 24 h after collection. We conclude that both MRD assays yield generally concordant results. Their combined use should enable MRD monitoring in virtually all patients and prevent false-negative results due to clonal evolution or phenotypic shifts.

Adult acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a relatively rare neoplasm with a curability rate around 30% at 5 years. This consideration makes it imperative to dissect further the biological mechanisms of disease, in order to selectively implement an hitherto unsatisfactory success rate. The recognition of discrete ALL subtypes (some of which deserve specific therapeutic approaches, like T-lineage ALL (T-ALL) and mature B-lineage ALL (B-ALL)) is possible through an accurate combination of cytomorphology, immunophenotytpe and cytogenetic assays and has been a major result of clinical research studies conducted over the past 20 years. Two-three major prognostic groups are now easily identifiable, with a survival probability ranging from <10 to 20% (Philadelphia-positive ALL) to about 50-60% (low-risk T-ALL and selected patients with B-lineage ALL). These issues are extensively reviewed and form the basis of current knowledge. The second major point relates to the emerging importance of studies that reveal a dysregulated gene activity and its clinical counterpart. It is now clear that prognostication is a complex matter ranging from patient-related issues to cytogenetics to molecular biology, including the evaluation of minimal residual disease (MRD) and possibly gene array tests. On these bases, the role of a correct, highly personalised therapeutic choice will soon become fundamental. Therapeutic progress may be obtainable through a careful integration of chemotherapy, stem cell transplantation, and the new targeted treatments with highly specific metabolic inhibitors and humanised monoclonal antibodies.

TCRB gene rearrangements in childhood and adult precursor-B-ALL: frequency, applicability as MRD-PCR target, and stability between diagnosis and relapse

Using the multiplex PCR tubes of the BIOMED-2 Concerted Action, TCRB gene rearrangements were detected in 35% of childhood (n=161) and adult (n=172) precursor-B-ALL patients (Vbeta-(Dbeta)-Jbeta in 25%; Dbeta-Jbeta in 15%). The presence of TCRB rearrangements showed a significant relation with age (highest frequency of 46% between 5 and 10 years of age) and the presence of TEL-AML1 transcripts, and was associated with relatively high frequencies of IGK-Kde, TCRG, and Vdelta2-Jalpha rearrangements. In 62 out of 65 patients with Southern blot-detected Vbeta-(Dbeta)-Jbeta and/or Dbeta-Jbeta rearrangements, at least one TCRB gene rearrangement was detected by PCR. Based on combined Southern blot and PCR analysis, oligoclonal TCRB gene rearrangements were observed in only 12% of patients. Analysis of paired diagnosis and relapse samples (n=26) showed that 20 out of 24 (83%) Vbeta-(Dbeta)-Jbeta rearrangements and eight out of 14 (57%) Dbeta-Jbeta rearrangements remained stable. Using real-time quantitative PCR, a quantitative range < or =10(-4) was obtained in 64% of TCRB gene rearrangements and in 86% of cases a sensitivity < or =10(-4) was obtained. In conclusion, TCRB gene rearrangements occur in 35% of precursor-B-ALL patients and are relatively stable and sensitive PCR targets for detection of minimal residual disease, particularly if this concerns complete Vbeta-(Dbeta)-Jbeta rearrangements.

Flow cytometric analysis of BCL-2 can distinguish small numbers of acute lymphoblastic leukaemia cells from B-cell precursors

Flow cytometric identification of small numbers of precursor B-cell acute lymphoblastic leukaemia (B-ALL) cells in post-treatment marrow specimens could benefit from the identification of additional, easily detectable markers that could be used in most cases. In this study, we evaluate whether bcl-2 expression quantified by four-colour flow cytometry can be effectively used to discriminate precursor B-ALL blasts from normal B-cell precursors (haematogones) and function as a leukaemia-specific marker. Levels of bcl-2 in the 22 precursor B-ALL cases studied were found to be significantly higher (over sixfold higher on average) than those present in haematogone populations from 22 control marrow specimens. Higher relative levels of bcl-2 expression in the B-ALL cases were maintained with respect to both immature CD34+ and more mature CD34- haematogone subsets, and appeared stable. Dilutional studies indicated that multiparameter flow cytometry analysis using bcl-2 could identify precursor B-ALL blasts representing as few as 1% of CD19+ cells or 0.01% of total leucocytes in bone marrow specimens containing substantial numbers of haematogones. This study suggests that bcl-2 may be an important marker for flow cytometric detection and quantification of small numbers of residual precursor B-ALL cells in bone marrow specimens.

Improved outcome for children with acute lymphoblastic leukemia: results of Total Therapy Study XIIIB at St Jude Children's Research Hospital

St Jude Total Therapy Study XIIIB for childhood acute lymphoblastic leukemia (ALL) incorporated more stringent risk classification, early intensification of intrathecal chemotherapy, reinduction treatment, and the addition of dexamethasone to postremission therapy to increase the proportion of event-free survivors without jeopardizing their quality of life. Cranial irradiation was reserved for the 12% of patients who had T-cell ALL and a presenting leukocyte count of 100 x 10(9)/L or more, or CNS-3 (5 or more leukocytes/microL with identifiable blast cells in an atraumatic sample or the presence of cranial nerve palsy) status. Among the 247 consecutive patients enrolled in the study, 117 were classified as having lower-risk leukemia and received mainly antimetabolite-based continuation therapy; the 130 cases with higher-risk leukemia received more intensive continuation chemotherapy with multiple drug pairs administered in weekly rotation. The 5-year event-free survival estimate was 80.8% +/- 2.6% (SE); the 8-year rate was 78.6% +/- 5.8%. The 5-year cumulative risk of an isolated central nervous system (CNS) relapse was 1.7% +/- 0.8%, and that of isolated plus combined CNS relapse was 3.0% +/- 1.1%. The 5-year cumulative risks of etoposide-related myeloid malignancies were 1.8% +/- 1.3% in the lower-risk patients who received a cumulative dose of 1.2 g/m(2) and 5.0% +/- 2.0% in the higher-risk patients who received a cumulative dose of up to 14.4 g/m(2) (P = .18). Independent adverse prognostic features included the presence of MLL-AF4 or BCR-ABL fusion gene and minimal residual leukemia of 0.01% or more at the end of the 6-week remission induction phase. Our results suggest the efficacy of early intensification of intrathecal chemotherapy and provide the basis for studies omitting cranial irradiation altogether.

Minimal residual disease studies by flow cytometry in acute leukemia

Minimal residual disease (MRD) assays are increasingly important in the clinical management of patients with acute leukemia. Among the methods available for monitoring MRD, flow cytometry holds great promise for clinical application because of its simplicity and wide availability. Several studies have demonstrated strong correlations between MRD levels by flow cytometry during clinical remission and treatment outcome, lending support to the reliability of this approach. Flow-cytometric detection of MRD is based on the identification of immunophenotypic combinations expressed on leukemic cells but not on normal hematopoietic cells. Its sensitivity depends on the specificity of the immunophenotypes used to track leukemic cells and on the number of cells available for study. Immunophenotypes that allow detection of 1 leukemic cell in 10,000 normal cells can be identified in at least 90% of patients with acute lymphoblastic leukemia; immunophenotypes that allow detection of 1 leukemic cell in 1,000-10,000 normal cells can be identified in at least 85% of patients with acute myeloid leukemia. Identification of new markers of leukemia by gene array technology should lead to the design of simple and reliable antibody panels for universal monitoring of MRD. Here we review the relative advantages and disadvantages of flow cytometry for MRD studies, as well as results obtained in correlative studies with treatment outcome.

Clinical applications of DNA microarray analysis

Microarray technology provides a revolutionary macro-genetic and bioinformatic-rich platform for understanding human diseases. DNA microarrays facilitate the study of complex diseases, enabling several observations simultaneously that can become foundations for newer hypotheses-shifting us towards a non-reductionist approach to biological phenomenon. This appears of particular value for scientific and clinical dissection of tumor pathologies. Despite the tremendous potential presented by microarray technology for the investigation of disease, concrete insights and advances that translate to the clinical setting are only recently beginning to be tapped. Here, we discuss specific examples of how microarray technology is being integrated into our ever-evolving approach to clinical disease. We focus on molecular strategies for (a) disease classification, (b) disease outcome, and (c) disease mechanisms.

Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia after first relapse

Using flow cytometric techniques capable of detecting 0.01% leukemic cells, we prospectively studied minimal residual disease (MRD) in patients with acute lymphoblastic leukemia (ALL) after first relapse. At the end of remission reinduction, 41 patients had a bone marrow sample adequate for MRD studies; 35 of these were in morphologic remission. Of the 35 patients, 19 (54%) had MRD >/=0.01%, a finding that was associated with subsequent leukemia relapse. The 2-year cumulative incidence of second leukemia relapse was 70.2+/-12.3% for the 19 MRD-positive patients and 27.9+/-12.4% for the 16 MRD-negative patients (P=0.008). Among patients with a first relapse off therapy, 2-year second relapse rates were 49.1+/-17.8% in the 12 MRD-positive and 0% in the 11 MRD-negative patients (P=0.014); among those who received only chemotherapy after first relapse, the 2-year second relapse rates were 81.5+/-14.4% (n=12) and 25.0+/-13.1% (n=13), respectively (P=0.004). Time of first relapse and MRD were the only two significant predictors of outcome in a multivariate analysis. We conclude that MRD assays should be used to guide the selection of postremission therapy in patients with ALL in first relapse.