Minimal residual disease (MRD) in remission t(8;21) AML and in vivo differentiation detected by FISH and CD34+ cell sorting

A study for evaluation of different diagnostic approaches in acute leukemia in Egypt

Cytomorphology, cytochemistry, immunophenotyping, in addition to cytogenetic and molecular analyses have specific roles in the diagnosis and management of acute leukemias. This work was designed as a comparative study of different available methods for diagnosis of acute leukemia. The study comprised 47 cases with acute leukemia (21 cases with ALL and 26 cases with AML). Peripheral blood and bone marrow samples were subjected to through morphological examination of Leishman-stained smears, cytochemical analysis, immunophenotyping, conventional cytogenetic banding analysis, fluorescence in situ hybridization (FISH) for selected cases, and RT-PCR for detection of BCR-ABL rearrangement. The results of the study revealed that careful examination of Romanowsky-stained peripheral blood and BM films is fundamental in the diagnosis of acute leukemias, and when considered together with clinical and hematological features, indicates which of the more specialized techniques are most likely to be useful. The major role of cytochemistry was in the diagnosis of AML, while the major role of immunophenotyping was in the diagnosis of acute leukemia, which is not obviously myeloid. Apart from identification of chromosomal abnormalities unique to specific subtypes of leukemia, cytogenetic analysis had a salient impact on anticipating the prognosis and treatment outcome in acute leukemias. We could conclude that the techniques used in this study are considered complementary rather than alternatives and that stepwise employment of strategies is more cost effective than doing all the tests simultaneously.

Should evaluation for minimal residual disease be routine in acute myeloid leukemia?

PURPOSE OF REVIEW

In patients with acute myeloid leukemia (AML), measuring response to treatment is essential to guide clinical decisions. Methods for detecting disease beyond the resolution limit of morphology (i.e., minimal residual disease, MRD) are now widely available. We here discuss their merits and the results of side-to-side comparisons.

RECENT FINDINGS

The ever-increasing comprehension of the molecular genetics of AML has led to the identification of targets for molecular monitoring of MRD in the majority of AML cases. Likewise, virtually all cases express aberrant immunophenotypes suitable for MRD monitoring by flow cytometry, a progress bolstered by powerful new-generation instruments. The clinical significance of MRD monitoring by either approach has been corroborated by recent results. However, with few exceptions, most of the studies continue to rely on retrospectively determined cut-off levels and time points. Moreover, when applied in parallel, the two approaches have yielded contradictory results.

SUMMARY

MRD monitoring can help predicting the risk of relapse better than morphology and also provide endpoints for clinical testing of experimental agents. MRD can be applied to guide therapy but one must carefully consider the characteristics of the methods used and the degree of expertise of the laboratory performing the test.

Cell sorting in cancer research--diminishing degree of cell heterogeneity

Increasing evidence of intratumor heterogeneity and its augmentation due to selective pressure of microenvironment and recent achievements in cancer therapeutics lead to the need to investigate and track the tumor subclonal structure. Cell sorting of heterogeneous subpopulations of tumor and tumor-associated cells has been a long established strategy in cancer research. Advancement in lasers, computer technology and optics has led to a new generation of flow cytometers and cell sorters capable of high-speed processing of single cell suspensions. Over the last several years cell sorting was used in combination with molecular biological methods, imaging and proteomics to characterize primary and metastatic cancer cell populations, minimal residual disease and single tumor cells. It was the principal method for identification and characterization of cancer stem cells. Analysis of single cancer cells may improve early detection of tumors, monitoring of circulating tumor cells, evaluation of intratumor heterogeneity and chemotherapeutic treatments. The aim of this review is to provide an overview of major cell sorting applications and approaches with new prospective developments such as microfluidics and microchip technologies.

Image cytometry-based detection of aneuploidy by fluorescence in situ hybridization in suspension

Cytogenetic abnormalities are important diagnostic and prognostic criteria for hematologic malignancies. Karyotyping and fluorescence in situ hybridization (FISH) are the conventional methods by which these abnormalities are detected. The sensitivity of these microscopy-based methods is limited by the abundance of the abnormal cells in the samples and therefore these analyses are commonly not applicable to minimal residual disease (MRD) stages. A flow cytometry-based imaging approach was developed to detect chromosomal abnormalities following FISH in suspension (FISH-IS), which enables the automated analysis of several log-magnitude higher number of cells compared with the microscopy-based approaches. This study demonstrates the applicability of FISH-IS for detecting numerical chromosome aberrations, establishes accuracy, and sensitivity of detection compared with conventional FISH, and feasibility to study procured clinical samples of acute myeloid leukemia (AML). Male and female healthy donor peripheral blood mononuclear cells hybridized with combinations of chromosome enumeration probes (CEP) 8, X, and Y served as models for disomy, monosomy, and trisomy. The sensitivity of detection of monosomies and trisomies amongst 20,000 analyzed cells was determined to be 1% with a high level of precision. A high correlation (R(2) = 0.99) with conventional FISH analysis was found based on the parallel analysis of diagnostic samples procured from 10 AML patients with trisomy 8 (+8). Additionally, FISH-IS analysis of samples procured at the time of clinical remission demonstrated the presence of residual +8 cells indicating that this approach may be used to detect MRD and associated chromosomal defects.

Acute Myelogenous Leukemia with t(8;21)—Identification of a Specific Immunophenotype

Association between certain surface markers and acute myelogenous leukemia (AML) with t(8;21) has been described. The specificity and the predictive values of these markers have never been assessed. In this study, we aimed, to explore whether a specific pattern could predict for this translocation. Of 405 consecutive AML, 18 (4.4%) had the t(8;21). Patients with this cytogenetic abnormality showed higher frequency of CD34 (P = 0.003), HLA-DR (P = 0.03), Tdt (P = 0.02), CD19 (P < 0.0001), and CD56 (P < 0.0001) and lower CD33 (P = 0.0001). Taken singly, the sensitivity of these markers for AML with t(8;21) ranged between 39 and 100% with CD34+ having the highest and CD33- having the lowest and the positive predictive values (PPV) ranged between 5 and 21% with CD19+ having the highest and HLA-DR+ having the lowest. When combinations of different markers were analyzed by multivariate analysis, the pattern CD34+/HLA-DR+/MPO+ was found to have the highest sensitivity (100%) with a PPV of 14% and the pattern CD34+/CD19+/CD56+ had the highest PPV (100%) with a sensitivity of 67%. We conclude that AML with t(8;21) is better identified by a combination of markers than by a single antigen pattern, the absence of CD34+, HLA-DR+ or MPO+ would preclude and the expression of the pattern CD34+/CD19+/CD56+ is highly predictive and could serve as a screening criteria for the t(8;21).

FISH glossary: an overview of the fluorescence in situ hybridization technique

The introduction of FISH (fluorescence in situ hybridization) marked the beginning of a new era for the study of chromosome structure and function. As a combined molecular and cytological approach, the major advantage of this visually appealing technique resides in its unique ability to provide an intermediate degree of resolution between DNA analysis and chromosomal investigations while retaining information at the single-cell level. Used to support large-scale mapping and sequencing efforts related to the human genome project, FISH accuracy and versatility were subsequently capitalized on in biological and medical research, providing a wealth of diverse applications and FISH-based diagnostic assays. The diversification of the original FISH protocol into the impressive number of procedures available these days has been promoted throughout the years by a number of interconnected factors: the improvement in sensitivity, specificity and resolution, together with the advances in the fields of fluorescence microscopy and digital imaging, and the growing availability of genomic and bioinformatic resources. By assembling in a glossary format many of the "acronymed" FISH applications published so far, this review intends to celebrate the ability of FISH to re-invent itself and thus remain at the forefront of biomedical research.

Quantitation of Minimal Residual Disease in Acute Myeloid Leukemia by Tryptase Monitoring Identifies a Group of Patients with a High Risk of Relapse

PURPOSE

Recent data suggest that tryptase is produced by blast cells in a group of patients with acute myeloid leukemia (AML). In these patients, serum tryptase levels are elevated at diagnosis and decrease to normal (<15 ng/mL) or near normal values in those achieving complete hematologic remission (CR) after chemotherapy.

PATIENTS

In this study, we examined the value of tryptase as a marker of minimal residual AML. In 61 patients with de novo AML exhibiting elevated serum tryptase (>15 ng/mL) at diagnosis, tryptase levels were measured serially during and after chemotherapy by a fluoroenzyme immunoassay.

RESULTS

Of the 61 patients, 42 (68.9%) entered hematologic CR in response to induction chemotherapy. Twenty-nine of these 42 patients also entered biochemical remission (BR) defined by a decrease of tryptase levels to normal (<15 ng/mL). The remaining 13 patients exhibited elevated enzyme levels despite of hematologic CR. As assessed by multivariate analysis, the elevated tryptase in CR was found to be an independent prognostic variable concerning disease-free survival. Thus, AML relapses occurred in 15 of 29 patients with CR + BR (52%) and in 12 of 13 patients with CR without BR (92%), resulting in a significantly reduced probability of continuous CR for patients with CR without BR (P < 0.05). In all patients with continuous hematologic CR, tryptase levels remained constantly normal, whereas a recurrent elevation of tryptase in CR was invariably followed by a hematologic relapse.

CONCLUSION

A persistently elevated tryptase level in AML in CR is indicative of minimal residual AML and associated with a high risk of relapse.

Prognostic factors in acute myeloid leukemia

PURPOSE OF REVIEW

Cytogenetics offers the most important prognostic information at both presentation and relapse. However, this classification appears to be insufficient, especially for patients presenting with standard-risk cytogenetics, whose relapse risk is variable. Other prognostic factors, stratifying this heterogeneous group of patients into more clearly defined risk groups, are warranted.

RECENT FINDINGS

Several molecular markers have been described that predict for long-term outcome in this heterogeneous group of patients; however, there is as yet no consensus as to the prognostic significance of each. Time to morphologic and molecular remission may also be important; however, further studies are warranted to establish their prognostic role in acute myeloid leukemia.

SUMMARY

Much has been learnt over the past decade and a better understanding of disease biology, determined by gene expression profiling and proteomic analyses, may help to target therapy and improve the outcome.

Detection of minimal residual disease in acute myelogenous leukemia

Acute myelogenous leukemia (AML) is considered to be in complete remission when fewer than 5% of the cells in bone marrow are blasts. Nevertheless, approximately two thirds of patients relapse due to persisting leukemic blasts. The persistence of these cells, below the threshold of morphological detection, is termed minimal residual disease (MRD) and various methods are used for its detection. These methods include classical cytogenetics, fluorescence in situ hybridization, qualitative and quantitative RT-PCR and multiparametric flow cytometry. Currently, less than half of the AML patients have a specific marker detectable by RT-PCR techniques. The major specific molecular markers are involvement of the MLL gene with up to 50 different partners and partial tandem duplications, the core binding factor leukemias with AML1/ETO and CBFbeta/MYH11 rearrangements, PML/RARalpha in acute promyelocytic leukemia, internal tandem duplications and mutations of FLT3 and some other rare translocations. In addition, several other genes show abnormal expression levels in AML, including the Wilms tumor gene, the PRAME gene and Ig/TCR rearrangements. Most of these genetic abnormalities can be detected by qualitative but more importantly by quantitative RT-PCR. The kinetics of disappearance of molecular markers in AML differs between the various types of leukemias, although at least a 2 log reduction of transcript after induction chemotherapy is necessary for long-term remission in all types. Conversely, the change of PCR from negativity to positivity is highly predictive of relapse. Whereas in acute lymphoblastic leukemia, multiparametric flow cytometry is an established method for MRD detection, this is less so in AML. The reason is the absence of well-characterized leukemia-specific antigens and the existence of phenotypic changes at relapse. On the other hand, this method is convenient due to its simplicity and universal applicability. In conclusion, several methods can be used for MRD detection in AML patients; each has its pros and cons. Several issues still remain to be settled including the choice of the best method and the timing for MRD monitoring and above all the practical clinical implications of MRD in the various types of AML.

Relevance of pathologic classifications and diagnosis of acute myeloid leukemia to clinical trials and clinical practice

Many new insights into the diagnosis, pathogenesis, clinical manifestation, treatment and prognosis of patients with AML reflect the heterogeneity of the disease. The initial descriptions of the various subtypes of AML, established by the FAB classification, were based on morphology and cytochemical stains. Although morphology remains the foundation for the diagnosis, additional diagnostic studies including immunophenotyping, cytogenetic evaluation, and molecular genetic studies have become critical, and in some specific cases, mandatory, complementary tools. Several specific subtypes of AML are now treated with directed or targeted therapy. Acute promyelocytic leukemia is currently the only example of a subtype of AML to which specific therapy targeted to a molecular genetic abnormality is available and this subtype now is highly curable. Future studies will address newly identified prognostic factors and gene mutations such as FLT3, Wilm's tumor (WTI), and CEBPA which will enable the further pathologic classification of patients with AML. Finally, microarray analysis will likely identify genes critically involved in the pathogenesis of specific pathologic subtypes.

Acute Philadelphia chromosome-positive leukemia in an adolescent boy after liver transplantation

Acute leukemia is an untoward event following immunosuppression for solid organ transplantation and is related to the oncogenic effects of Epstein-Barr viral infections. The authors report a case of acute, Philadelphia chromosome-positive, T-cell lymphoblastic leukemia following liver transplantation. Molecular typing demonstrated a minor bcr-abl rearrangement (190 kD), which persisted in remission in 71% of peripheral neutrophils as determined by fluorescence in situ hybridization. The authors conclude that this patient may have presented in a lymphoid blast crisis of chronic myelogenous leukemia with an acute T-cell leukemia/lymphoma syndrome.

Molecular cytogenetics in solid tumors: laboratorial tool for diagnosis, prognosis, and therapy

The remarkable progress in the understanding of leukemogenesis was soundly sustained by methodological developments in the cytogenetic field. Nonrandom chromosomal abnormalities frequently associated with specific types of hematological disease play a major role in their diagnosis and have been demonstrated as independent prognostic indicators. Molecular pathways altered by chimeric or deregulated proteins as a consequence of chromosomal abnormalities have also significantly contributed to the development of targeted therapies, and cytogenetic assays are valuable for selecting patients for treatment and monitoring outcome. In solid tumors, significantly high levels of chromosome abnormalities have been detected, but distinction between critical and irrelevant events has been a major challenge. Consequently, the application of cytogenetic technology as diagnostic, prognostic, or therapeutic tools for these malignancies remains largely under appreciated. The emergence of molecular-based techniques such as fluorescence in situ hybridization was particularly useful for solid malignancies, and the spectrum of their application is rapidly expanding to improve efficiency and sensitivity in cancer prevention, diagnosis, prognosis, and therapy selection, alone or in combination with other diagnostic methods. This overview illustrates current uses and outlines potential applications for molecular cytogenetics in clinical oncology.

Detection of minimal residual disease in acute myeloid leukemia

Acute myeloid leukemia (AML) is a curable malignancy, but its cure rate remains disappointingly low. Accurate quantitation of residual AML cells would allow individualization of therapy and thereby increase the likelihood of cure for each patient. Techniques that are being studied for residual disease detection include molecular assays for abnormalities that are present in subsets of AML patients, and multiparameter flow cytometry, which has broader applicability. Although significant advances have been made in the development of assays for monitoring residual disease, and particularly in techniques for molecular quantitation, additional refinement and validation are needed before these assays can be applied routinely in clinical management.