Monitoring minimal residual disease and predicting relapse in APL by quantitating PML-RARalpha transcripts with a sensitive competitive RT-PCR method

The Application of GHRH Antagonist as a Treatment for Resistant APL

GHRH is a hypothalamic peptide shown to stimulate the proliferation of malignant cells in humans. We have previously shown that the use of GHRH antagonist MIA-602 successfully suppressed the growth of many human cancer cell lines, spanning more than 20 types of cancers. In this study, we demonstrate the presence of GHRH-R in the NB4, NB4-RAA, and K-562 model cell lines. Furthermore, we demonstrate the inhibited proliferation of all three cell lines in vitro after incubation with MIA-602. The treatment of xenografts of human APL cell lines with MIA-602 led to a significant reduction in tumor growth. Additionally, combination therapy with both doxorubicin (DOX) and MIA-602 showed a marked synergistic effect in reducing the proliferation of the K-562 AML cell line. These findings suggest that MIA-602 could be utilized to address resistance to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) therapies, as well as in augmenting anthracycline-based regimens.

Circulating lnc-LOC as a novel noninvasive biomarker in the treatment surveillance of acute promyelocytic leukaemia

BACKGROUND

Acute promyelocytic leukaemia (APL) is a unique subtype of acute myeloid leukaemia (AML) characterized by haematopoietic failure caused by the accumulation of abnormal promyelocytic cells in bone marrow (BM). However, indispensable BM biopsy frequently afflicts patients in leukaemia surveillance, which increases the burden on patients and reduces compliance. This study aimed to explore whether the novel circulating long noncoding RNA LOC100506453 (lnc-LOC) could be a target in diagnosis, assess the treatment response and supervise the minimal residual disease (MRD) of APL, thereby blazing a trail in noninvasive lncRNA biomarkers of APL.

METHODS

Our study comprised 100 patients (40 with APL and 60 with non-APL AML) and 60 healthy donors. BM and peripheral blood (PB) sample collection was accomplished from APL patients at diagnosis and postinduction. Quantitative real-time PCR (qRT-PCR) was conducted to evaluate lnc-LOC expression. A receiver operating characteristic (ROC) analysis was implemented to analyse the value of lnc-LOC in the diagnosis of APL and treatment monitoring. For statistical analysis, the Mann-Whitney U test, a t test, and Spearman's rank correlation test were utilized.

RESULTS

Our results showed that BM lnc-LOC expression was significantly different between APL and healthy donors and non-APL AML. lnc-LOC was drastically downregulated in APL patients' BM after undergoing induction therapy. Lnc-LOC was upregulated in APL cell lines and downregulated after all-trans retinoic acid (ATRA)-induced myeloid differentiation, preliminarily verifying that lnc-LOC has the potential to be considered a treatment monitoring biomarker. PB lnc-LOC was positively correlated with BM lnc-LOC in APL patients, non-APL AML patients and healthy donors and decreased sharply after complete remission (CR). However, upregulated lnc-LOC was manifested in relapsed-refractory patients. A positive correlation was revealed between PB lnc-LOC and PML-RARα transcript levels in BM samples. Furthermore, we observed a positive correlation between PB lnc-LOC and BM lnc-LOC expression in APL patients, suggesting that lnc-LOC can be utilized as a noninvasive biomarker for MRD surveillance.

CONCLUSIONS

Our study demonstrated that PB lnc-LOC might serve as a novel noninvasive biomarker in the treatment surveillance of APL, and it innovated the investigation and application of newly found lncRNAs in APL noninvasive biomarkers used in diagnosis and detection.

Acute promyelocytic leukemia derived extracellular vesicles conserve PML-RARα transcript from storage-inflicted degradation: a stable diagnosis tool in APL patients

The early death, which is more common in acute promyelocytic leukemia (APL) patients rather than other types of acute myelocytic leukemia (AML) highlights the importance of appropriate diagnostic method for early detection of this disease. The low sensitivity of the conventional methods, low tumor burden in some patients, and the need for bone marrow sampling are some of the diagnostic challenges on the way of proper detection of APL. Given these, we aimed to compare the efficacy of extracellular vesicles (EVs), as a diagnostic tool, with the existing methods. RT-PCR, qPCR, and flow cytometry were applied on EVs and their corresponding associated cellular component collected from 18 APL new cases, 23 patients with minimal residual disease (MRD), and NB4 cell line. RT-PCR results were positive in both cellular and vesicular components of all new cases, NB4 cells, and EVs in contrary to MRD cases. Normalized copy numbers (NCN) of PML-RARα were 5100 and 3950 for cell and EVs, respectively (p < 0.05). There was a significant difference in the NCN of PML-RARα between cells and EVs in BM samples. Investigating the effect of storage at room temperature revealed that PML-RARα level was retained near to the baseline level in EVs, but there was a significant reduction in its copy number in the cellular component during 7 days. Taken together, given to the acceptable stability, EVs could be introduced as a non-invasive liquid biopsy that alongside existing methods could remarkably change the paradigm of APL diagnostic approaches.

Synergistic Effect of Simvastatin and Romidepsin on Gamma-globin Gene Induction

OBJECTIVE

Hemoglobinopathies such as beta-thalassemia and sickle cell disease (SCD) are inherited disorders that are caused by mutations in beta-globin chain. Gamma-globin gene reactivation can ameliorate clinical manifestations of betathalassemia and SCD. Drugs that induce fetal hemoglobin (HbF) can be promising tools for treatment of beta-thalassemia and SCD patients. Recently, it has been shown that Simvastatin (SIM) and Romidepsin (ROM) induce HbF. SIM is a BCL11a inhibitor and ROM is a HDAC inhibitor and both of these drugs are Food and Drug Administration (FDA)-approved for hypercholesterolemia and cutaneous T-cell lymphoma respectively. Our aim was to evaluate the synergistic effects of these drugs in inducing HbF.

MATERIALS AND METHODS

In our experimental study, we isolated CD34+ cells from five cord blood samples that were cultured in erythroid differentiation medium containing ROM and Simvastatin. Then Gamma-globin, BCL11a and HDAC gene expression were evaluated on the 7th and 14th day of erythroid differentiation by real-time polymerase chain reaction (PCR) and immunocytochemistry.

RESULTS

Our results showed that combination of SIM and ROM significantly increased Gamma-globin gene expression and inhibit BCL11a and HDAC expression compared to results of using each of them alone. SIM and ROM lead to 3.09- fold increase in HbF production compared to the control group. Also, SIM inhibited BCL11a expression (0.065-fold) and ROM inhibited HDAC1 expression (0.47-fold) as two important inhibitors of HbF production after birth.

CONCLUSION

We propose combination therapy of these drugs may be ameliorate clinical manifestation in beta-thalassemia and SCD with at least side effects and reduce the need for blood transfusion.

Leukemia Associated Antigens: Their Dual Role as Biomarkers and Immunotherapeutic Targets for Acute Myeloid Leukemia

Leukemia associated antigens (LAAs) are being increasingly identified by methods such as cytotoxic T-lymphocyte (CTL) cloning, serological analysis of recombinant cDNA expression libraries (SEREX) and mass spectrometry (MS). In additional, large scale screening techniques such as microarray, single nucleotide polymorphisms (SNPs), serial analysis of gene expression (SAGE) and 2-dimensional gel electrophoresis (2-DE) have expanded our understanding of the role that tumor antigens play in the biological processes which are perturbed in acute myeloid leukemia (AML). It has become increasingly apparent that these antigens play a dual role, not only as targets for immunotherapy, but also as biomarkers of disease state, stage, response to treatment and survival. We need biomarkers to enable the identification of the patients who are most likely to benefit from specific treatments (conventional and/or novel) and to help clinicians and scientists improve clinical end points and treatment design. Here we describe the LAAs identified in AML, to date, which have already been shown to play a dual role as biomarkers of AML disease.

FLT3 and NPM-1 mutations in a cohort of acute promyelocytic leukemia patients from India

BACKGROUND

Acute promyelocytic leukemia (APL) with t (15;17) is a distinct category of acute myeloid leukemia (AML) and is reported to show better response to anthracyclin based chemotherapy. A favorable overall prognosis over other subtypes of AML has been reported for APL patients but still about 15% patients relapse.

METHODS

This study evaluated the presence of Famus like tyrosine kinase-3 (FLT3) and nucleophosmin-1 (NPM1) gene mutations in a cohort of 40 APL patients. Bone marrow/peripheral blood samples from patients at the time of diagnosis and follow-up were processed for immunophenotyping, cytogenetic markers and isolation of DNA and RNA. Samples were screened for the presence of mutations in FLT3 and NPM1 genes using polymerase chain reaction followed by sequencing.

RESULTS

Frequency of FLT3/internal tandem duplication and FLT3/tyrosine kinase domain was found to be 25% and 7% respectively. We observed a high frequency of NPM1 mutation (45%) in the present population of APL patients.

Utilization of molecular phenotypes to detect relapse and optimize the management of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by a unique genetic aberration, the t(15;17) chromosome translocation. Translocation breakpoints are located within the promyelocytic leukemia (PML) locus on chromosome 15 and the retinoic acid receptor alpha (RARA) locus on chromosome 17. In the past 2 decades, critical advances have been made in understanding the molecular pathogenesis of APL. APL represents a paradigm for molecularly targeted therapy in cancer and an extraordinary model for translational research in medicine. In fact, the release of differentiation block upon treatment of APL with all-trans-retinoic acid (ATRA) has represented the first example of targeted therapy in human cancer. More recently, the advent of arsenic trioxide (ATO) has allowed further progress in the management of this disease through improved outcomes in patients receiving this agent in combination with ATRA. Finally, optimization of therapy and minimization of toxicity is feasible in this disease through careful monitoring of residual disease using polymerase chain reaction-based approaches targeting the PML-RARA fusion gene.

Real-time PCR analysis of PML-RARα in newly diagnosed acute promyelocytic leukaemia patients treated with arsenic trioxide as a front-line therapy

BACKGROUND

Recently, patients with acute promyelocytic leukaemia (APL) have experienced significant clinical gains after treatment with arsenic trioxide. However, the use of this agent as a front-line therapy for newly diagnosed patients is unclear.

PATIENTS AND METHODS

Of 95 newly diagnosed APL patients, 85 patients who achieved complete remission (CR) were sequentially evaluated during a 4-60 month period by conventional RT-PCR. A total of 30 patients (six relapsed and 24 in continued CR) were selected and monitored by quantitative real-time PCR (RQ-PCR) assay. The PML-RARalpha fusion transcripts values were normalised to every 10(6) copies of G6PDH transcripts (NQ).

RESULTS

RQ-PCR analyses showed a rapid rate of clearance of NQ levels during the courses of arsenic therapy. In the majority of patients in CR, the NQ levels were below 5 x 10(2) in peripheral blood (PB) samples. In all the relapsed cases with follow-up intervals of 1-6 months (median 3 months) clinical relapse was predictable by increasing NQ level above this threshold.

CONCLUSIONS

Our study highlights the usefulness of PB and the definition of threshold level for early prediction of relapse. The threshold level correlates well with risk of relapse; therefore, transcript ratio below the level should be regarded as a goal in the clinical management of this disease.

Examination of Stability of Bone Marrow Blood RNA in the PAXgene Tube

The PAXgene RNA blood collection tube is used for RNA of peripheral blood (PB) and the stability of PB RNA in this tube has already been reported. However, the stability of bone marrow blood (BM) RNA in the PAXgene tube is unknown. Thus, we examined the stability of BM RNA in the PAXgene tubes. BM from leukemia patients was collected into PAXgene and EDTA tubes and stored at 4 degrees C for 5 days. RNA isolated from both tubes was analyzed by a quantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis. Porphobilinogen deaminase (PBGD) mRNA of BM (as high-expression mRNA) and Wilms tumor suppressor (WT1) mRNA of BM (as low-expression mRNA) and very low copies of major BCR-ABL mRNA (as minimal residual disease of leukemia) of leukemia of BM were quantified by a LightCycler system. RNA yield from the PAXgene tubes and the intensity of 28S rRNA bands on RNA electrophoresis showed a degradation trend. However, the intensity of 18S rRNA bands from the PAXgene tubes remained. The expression of PBGD and WT1 of BM in the PAXgene tubes did not decrease for 5 days. The very low copies of major BCR-ABL mRNA in the PAXgene tubes were detectable on day 5 but those in the EDTA tubes were not detectable. Therefore, the PAXgene tube can be used for BM samples in a quantitative RT-PCR of the fusion gene transcripts of leukemia.

Rhabdomyosarcoma: molecular diagnostics of patients classified by morphology and immunohistochemistry with emphasis on bone marrow and purged peripheral blood progenitor cells involvement

Two histologically distinct subtypes of rhabdomyosarcomas (RMS), embryonal and alveolar, are different in many aspects, such as age distribution, primary site, and clinical outcome. We analyzed a group of 30 patients with RMS. The aim was to broaden the spectrum of diagnostic tools in evaluating the primary tumors, their recurrences and/or metastases, and to extend the diagnostic boundary to bone marrow and purged peripheral progenitor blood cell samples. We have performed the RT-PCR assay to analyze RMS for the presence of expression of MyoD1 gene and for the presence of chimeric transcripts PAX3/FKHR or PAX7/FKHR. MyoD1 gene expression was found in all 30 patients in samples from primary tumors. The chimeric transcripts PAX/FKHR were identified in 13 of 15 patients with alveolar RMS. Furthermore, the fusion transcript PAX7/FKHR was identified in 2 of 15 patients with RMS classified as embryonal by histology. Bone marrow samples (12) and peripheral blood progenitor cell specimens (13) in ten patients were examined by RT-PCR. We were able to identify 7 patients with bone marrow involvement and/or with contamination of peripheral blood progenitor cells by the tumor cells. We demonstrate that employing molecular diagnostics has an impact on staging, therapy monitoring and recognition of malignant cells at the tumor resection margins.

Prognostic value of real-time quantitative PCR (RQ-PCR) in AML with t(8;21)

Despite the favorable prognosis of patients with acute myeloid leukemia (AML) with t(8;21)(q22;q22) translocation, relapses still occur in about 30% of the cases but no initial factors can strongly predict the risk of relapse. Several recent studies suggest that monitoring minimal residual disease (MRD) may identify patients at risk of relapse. We prospectively monitored AML1-ETO rearrangement by real-time quantitative PCR (RQ-PCR) in 21 patients uniformly treated in our center. Blood (PB) and bone marrow (BM) samples were collected during and after therapy. At diagnosis, levels of AML1-ETO transcript showed large variations and there was a trend for a higher relapse rate in patients with high pretreatment expression levels (P=0.065). After induction therapy, absolute transcript levels (below 10(-3), compared to Kasumi cell line), or a greater than 3 log decrease by comparison to diagnosis levels, were significant predictors of the absence of relapse (P=0.02 and P=0.02, respectively). MRD levels after consolidation therapy were also significant indicators of relapse (P=10(-5)). Comparison of BM and PB samples showed similar sensitivity for detecting AML1-ETO transcript. In conclusion, RQ-PCR appears to be an early predictive factor of the relapse risk in AML with t(8;21). PB samples can be used adequately to evaluate the level of MRD by this technique.

Pathogenesis, diagnosis and monitoring of residual disease in acute promyelocytic leukaemia

The clinical course of acute promyelocytic leukaemia (APL) has changed over the last 25 years from one that was fatal for the majority of patients to representing one of the most curable subtypes of acute myeloid leukaemia. Besides improved supportive care this has mainly been achieved through the introduction of novel targeted therapies in the form of all-trans retinoic acid (ATRA) and arsenic trioxide that specifically address the underlying molecular lesion. APL is characterized by chromosomal rearrangements of 17q21 leading to the formation of fusion proteins involving retinoic acid receptor alpha (RARA). To date five different fusion partners of RARA have been identified, but the vast majority of cases are characterized by the presence of the t(15;17)(q22;q12-21), which involves the promyelocytic leukaemia (PML) gene. The identification of different breakpoint microclusters within RARA intron 2 suggests that sequence-associated or structural factors play a role in the formation of the t(15;17). In addition, the comparison of forward and reverse genomic junctions has revealed microhomologies, deletions and/or duplications of either gene consistent with the hypothesis that the t(15;17) occurs by non-homologous recombination of DNA after processing of the double strand breaks by a dysfunctional DNA damage repair mechanism. The detection of the PML-RARA fusion gene by reverse-transcription polymerase chain reaction (RT-PCR) is routinely used for diagnosis and monitoring of minimal residual disease (MRD). In PML-RARA-positive APL about 70% of patients are expected to be cured with a combination of ATRA and anthracycline-based chemotherapy. However, relapse remains a major problem. The identification of patients at high risk of relapse and the development of risk-adapted treatment schedules are therefore clearly the most challenging tasks in the treatment of APL. Recent studies have shown that pre-emptive chemotherapy at the time of molecular relapse improves survival compared to treatment at the point of haematological relapse. Quantitative RT-PCR technology is expected to further improve the predictive value of MRD monitoring and therefore to guide therapy in order to reduce the rate of relapses and to increase rates of cure in high-risk patients.

Monitoring PML-RARalpha in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by a translocation between the promyelocytic leukemia gene (PML) on chromosome 15 and the retinoic acid receptor-alpha (RARalpha) gene on chromosome 17. Reverse-transcription polymerase chain reaction (RT-PCR) amplification of PML-RARalpha messenger RNA can establish the diagnosis of APL, predict response to all-trans retinoic acid and arsenic trioxide, detect minimal residual disease, and predict relapse. Quantitative "real-time" RT-PCR techniques may improve residual disease assessment by facilitating more rapid and standardized results. APL provides a useful model in which therapy is targeted to an underlying genetic aberration and treatment is adapted based on monitoring of residual disease.

Acute myeloid leukemia

In this chapter, Drs. Keating and Willman review recent advances in our understanding of the pathophysiology of acute myeloid leukemia (AML) and allied conditions, including the advanced myelodysplastic syndromes (MDS), while Drs. Goldstone, Avivi, Giles, and Kantarjian focus on therapeutic data with an emphasis on current patient care and future research studies. In Section I, Dr. Armand Keating reviews the role of the hematopoietic microenvironment in the initiation and progression of leukemia. He also discusses recent data on the stromal, or nonhematopoietic, marrow mesenchymal cell population and its possible role in AML. In Section II, Drs. Anthony Goldstone and Irit Avivi review the current role of stem cell transplantation as therapy for AML and MDS. They focus on data generated on recent Medical Research Council studies and promising investigation approaches. In Section III, Dr. Cheryl Willman reviews the current role of molecular genetics and gene expression analysis as tools to assist in AML disease classification systems, modeling of gene expression profiles associated with response or resistance to various interventions, and identifying novel therapeutic targets. In Section IV, Drs. Hagop Kantarjian and Francis Giles review some promising agents and strategies under investigation in the therapy of AML and MDS with an emphasis on novel delivery systems for cytotoxic therapy and on targeted biologic agents.

Acute promyelocytic leukemia: a model for the role of molecular diagnosis and residual disease monitoring in directing treatment approach in acute myeloid leukemia

Acute promyelocytic leukemia (APL) is characterized by a number of features that underpin the need for rapid and accurate diagnosis and demand a highly specific treatment approach. These include the potentially devastating coagulopathy, sensitivity to anthracycline-based chemotherapy regimens, as well as unique responses to all-trans retinoic acid and arsenic trioxide that have revolutionized therapy over the last decade. The chromosomal translocation t(15;17) which generates the PML-RARalpha fusion gene has long been considered the diagnostic hallmark of APL; however, this abnormality is not detected in approximately 10% cases with successful karyotype analysis. In the majority of these cases, the PML-RARalpha fusion gene is still formed, resulting from insertion events or more complex rearrangements. These cases share the beneficial response to retinoids and favorable prognosis of those with documented t(15;17), underscoring the clinical relevance of molecular analyses in diagnostic refinement. In other cases of t(15;17) negative APL, various chromosomal rearrangements involving 17q21 have been documented leading to fusion of RARalpha to alternative partners, namely PLZF, NPM, NuMA and STAT5b. The nature of the fusion partner has a significant bearing upon disease characteristics, including sensitivity to retinoids and arsenic trioxide. APL has provided an exciting treatment model for other forms of AML whereby therapeutic approach is directed towards cytogenetically and molecularly defined subgroups and further modified according to response as determined by minimal residual disease (MRD) monitoring. Recent studies suggest that rigorous MRD monitoring, coupled with pre-emptive therapy at the point of molecular relapse improves survival in the relatively small subgroup of PML-RARalpha positive patients with 'poor risk' disease. Advent of 'real-time' quantitative RT-PCR technology seems set to yield further improvements in the predictive value of MRD assessment, achieve more rapid sample throughput and facilitate inter- and intra-laboratory standardization, thereby enabling more reliable comparison of data between international trial groups.

Management of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) has become the most potentially curable subtype of acute myeloid leukemia (AML) in adults. With current treatment strategies that incorporate all-trans retinoic acid (ATRA), long-term disease-free survival and potential cure rates of 70% to 80% can be expected. Such progress reflects what can be accomplished with insights into the molecular pathogenesis of leukemia, identification of a molecular target, and rapid accrual to a series of clinical trials. The leukemic promyelocytes from patients with APL are uniquely susceptible to a variety of novel agents in addition to ATRA, including arsenic trioxide, and in preliminary studies, gemtuzumab ozogamicin, the immunoconjugate comprised of an anti-CD33 monoclonal antibody linked to the potent cytotoxic agent calicheamicin. Incorporation of such agents into the treatment of patients with high-risk disease may be an important future direction to pursue.

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.

Diagnosis and Molecular Monitoring of Acute Promyelocytic Leukemia Using DzyNA Reverse Transcription-PCR to Quantify PML/RARα Fusion Transcripts

Background: PML/RARα fusion transcripts provide a readily accessible marker for diagnosis of acute promyelocytic leukemia (APL) and for monitoring response to therapy. Survival rates are improved by therapies guided by such monitoring. We assessed the potential of DzyNA reverse transcription-PCR (RT-PCR) for measurement of PML/RARα fusion transcripts.

Methods: Parallel single-tube DzyNA RT-PCR protocols were developed to allow real-time fluorescent quantification of PML/RARα fusion transcripts and a low abundance control transcript, normal BCR. Calibration curves, generated using cell line RNA, allowed estimation of these transcripts in RNA from patients with APL at various stages of the disease.

Results: DzyNA RT-PCR calibration curves were linear for both transcripts over a broad range and demonstrated interassay variations of 12% (mean, 658 ng) and 10% (mean, 263 ng), respectively. The protocols detected low concentrations of transcripts and resolved twofold dilutions. PML/RARα mRNA was quantified in 10 patients at diagnosis and in 1 patient over a 7-year period. Monitoring of transcript concentrations effectively reflected the disease course in one patient and demonstrated that an increase in PML/RARα transcripts can be detected 4–6 months before hematologic relapse, with no false-positive results.

Conclusion: DzyNA RT-PCR has potential for use in clinical practice as a tool for diagnosis of APL and forsubsequent monitoring of minimal residual disease and detection of molecular relapse.

Assessing minimal residual disease (MRD) in leukemia: a changing definition and concept?

The term minimal residual disease (MRD) in its currently accepted application refers to low-level disease detected in a whole variety of clinical situations. It is used to describe residual disease after suboptimal induction chemotherapy, but at the same time refers to the lowest levels of disease potentially compatible with cure or to molecularly defined relapse after long-term remission. This discussion intends to redefine MRD into some biologically relevant subcategories which may warrant their own independent terminology.

The significance of minimal residual disease in patients with t(15;17)

Acute promyelocytic leukaemia (APL) is characterized by the t(15;17)(q22;q21) leading to the formation of PML-RARalpha and RARalpha-PML fusion genes which provide suitable targets for the assessment of minimal residual disease (MRD). Studies have focused upon detection of PML-RARalpha because, although assays for RARalpha-PML transcripts are more sensitive, they are not applicable to 25% of cases. Among patients receiving standard therapy (ATRA and anthracycline-based chemotherapy), qualitative assays using a nested reverse transcriptase-polymerase chain reaction (RT-PCR), which typically achieve sensitivities of 1 in 10(4), have been found to provide independent prognostic information suitable for directing an approach to treatment. Detection of PML-RARalpha at the end of consolidation, or subsequent recurrence of PCR positivity, heralds relapse, which may, however, be averted by additional therapy leading to improvements in survival for this "high-risk" subgroup of patients. MRD analysis has also proved of value in predicting response to autologous transplant procedures undertaken in second complete remission and in directing the need for additional therapy in the post-transplantation setting. Overall, these studies undertaken within the context of a relatively homogeneous disease entity confirm that MRD monitoring provides independent prognostic information, serving as a valuable model for improving treatment strategy in other molecularly defined subsets of acute myeloid leukaemia (AML). Nevertheless, conventional nested RT-PCR assays fail to detect residual disease in a significant proportion of patients who ultimately relapse, which may be a reflection of RNA quality and/or assay sensitivity. Therefore, it is hoped that "real-time" quantitative RT-PCR technology (RQ-PCR) which permits quantification of fusion gene transcripts in relation to endogenous control genes will be even more predictive of outcome and achieve greater standardization of MRD detection in the context of large-scale clinical trials.

Acute promyelocytic leukemia: evolving therapeutic strategies

Acute promyelocytic leukemia (APL) is now the most curable subtype of acute myeloid leukemia in adults. All-trans retinoic acid (ATRA), which induces differentiation of the leukemic cells into mature granulocytes, represents the important advance. The incorporation of ATRA in induction results in a high complete remission rate, leads to rapid resolution of the characteristic life-threatening coagulopathy, and, most importantly, decreases the relapse rate compared with treatment with chemotherapy alone. However, ATRA is associated with unique toxicities not observed with conventional cytotoxic chemotherapy. A number of clinical trials have been performed to define the optimal role of ATRA in the treatment of patients. The therapeutic strategies have rapidly evolved as a result of both single institution and large cooperative group trials. Arsenic trioxide and stem cell transplantation are effective treatments for patients with APL who relapse after or are refractory to ATRA-based therapy. As experience with ATRA and arsenic trioxide in patients with APL accumulates, a number of important questions arise that need to be addressed.