All-trans-retinoic acid in acute promyelocytic leukemia

The Importance of Diagnostic Cytogenetics on Outcome in AML: Analysis of 1,612 Patients Entered Into the MRC AML 10 Trial

Cytogenetics is considered one of the most valuable prognostic determinants in acute myeloid leukemia (AML). However, many studies on which this assertion is based were limited by relatively small sample sizes or varying treatment approach, leading to conflicting data regarding the prognostic implications of specific cytogenetic abnormalities. The Medical Research Council (MRC) AML 10 trial, which included children and adults up to 55 years of age, not only affords the opportunity to determine the independent prognostic significance of pretreatment cytogenetics in the context of large patient groups receiving comparable therapy, but also to address their impact on the outcome of subsequent transplantation procedures performed in first complete remission (CR). On the basis of response to induction treatment, relapse risk, and overall survival, three prognostic groups could be defined by cytogenetic abnormalities detected at presentation in comparison with the outcome of patients with normal karyotype. AML associated with t(8;21), t(15;17) or inv(16) predicted a relatively favorable outcome. Whereas in patients lacking these favorable changes, the presence of a complex karyotype, −5, del(5q), −7, or abnormalities of 3q defined a group with relatively poor prognosis. The remaining group of patients including those with 11q23 abnormalities, +8, +21, +22, del(9q), del(7q) or other miscellaneous structural or numerical defects not encompassed by the favorable or adverse risk groups were found to have an intermediate prognosis. The presence of additional cytogenetic abnormalities did not modify the outcome of patients with favorable cytogenetics. Subgroup analysis demonstrated that the three cytogenetically defined prognostic groups retained their predictive value in the context of secondary as well as de novo AML, within the pediatric age group and furthermore were found to be a key determinant of outcome from autologous or allogeneic bone marrow transplantation (BMT) in first CR. This study highlights the importance of diagnostic cytogenetics as an independent prognostic factor in AML, providing the framework for a stratified treatment approach of this disease, which has been adopted in the current MRC AML 12 trial.

all-Trans-retinoic acid reduces neointimal formation and promotes favorable geometric remodeling of the rat carotid artery after balloon withdrawal injury

BACKGROUND

The multifactorial and unpredictable nature of human restenosis will probably necessitate interventional strategies that target multiple processes involved in acute vascular narrowing. Retinoids (eg, all-trans-retinoic acid, atRA) represent a growing class of pleiotropic biological response modifiers with demonstrable efficacy in managing several pathological conditions. In this report, we have initiated studies to examine the hypothesis that atRA limits neointimal formation after experimental vascular injury.

METHODS AND RESULTS

Rats were predosed with atRA (30 mg . kg-1 . d-1 PO) or corn oil 4 days before balloon withdrawal injury (BWI) of the left common carotid artery and continued on this drug regimen for an additional 14 days. High-performance liquid chromatographic analysis documented therapeutic levels of atRA in serum and vascular tissue. atRA depressed peak DNA synthesis in the tunica media of BWI vessels (P<0.05). Histomorphometry revealed atRA-mediated reductions in neointimal area, neointimal cell number, and intimal/medial area ratio as well as significant increases in vessel wall perimeter (P<0. 05). Such changes in vascular architecture contributed to a 35% to 37% increase in the luminal area of BWI vessels exposed to atRA (P<0. 005 compared with controls).

CONCLUSIONS

atRA reduces neointimal mass and elicits favorable geometric remodeling of the injured rat carotid artery.

Retinoids potentiate transforming growth factor-beta activity in bovine endothelial cells through up-regulating the expression of transforming growth factor-beta receptors

Retinoic acid (RA) induces the activation of latent transforming growth factor-beta (TGF-beta) in bovine aortic endothelial cells (BAECs) via enhancement of cellular plasminogen activator (PA)/plasmin levels. The resultant TGF-beta suppresses the excessive fibrinolytic activity by decreasing PA expression and stimulating expression of the PA inhibitor, PA inhibitor-1 (PAI-1), and inhibits cell proliferation. Here, we report that, in this regulatory system, RA simultaneously up-regulates the expression of TGF-beta receptor types I and II, resulting in enhancement of TGF-beta activity in the cells. RA increased the numbers of high- and low-affinity binding sites for 125I-TGF-beta1 2.1-fold and 1.5-fold, respectively, without alteration of their Kd values. Affinity labeling and Western and Northern blotting studies showed that, following RA treatment, surface levels of both type I and type II receptors increased due to augmentation in their mRNA levels. The effect was dose- and time-dependent. Treatment with 1 microM RA for 15 hr increased mRNA levels of type I and II receptor threefold and eightfold, respectively. Pretreatment of BAECs with either RA or retinol lowered the concentration of TGF-beta1 required to suppress PA levels, to enhance PAI-1 levels, and to inhibit cell proliferation. Thus, retinoids may regulate cellular functions of BAECs not only by inducing the formation of active TGF-beta but also by stimulating TGF-beta receptor expression. This regulatory mechanism may sustain TGF-beta-mediated regulation of EC function at a focal site where RA is acting.

Leukemic Cellular Retinoic Acid Resistance and Missense Mutations in the PML-RAR Fusion Gene After Relapse of Acute Promyelocytic Leukemia From Treatment With All-trans Retinoic Acid and Intensive Chemotherapy

This study evaluated whether relapse of acute promyelocytic leukemia (APL) patients from clinical remissions achieved and/or maintained with all-trans retinoic acid (RA) in combination with intensive chemotherapy is associated with leukemic cellular resistance to RA and with alterations in the PML-RAR fusion gene. We studied matched pretreatment and relapse specimens from 12 patients who received variable amounts of RA, primarily in nonconcurrent combination with daunorubicin and cytarabine (DA) on Eastern Cooperative Oncology Group (ECOG) protocol E2491, and from 8 patients who received DA only on protocol E2491. Of 10 RA-treated patients evaluable for a change in APL cell sensitivity to RA-induced differentiation in vitro, 8 showed diminished sensitivity at relapse, whereas, of 6 evaluable patients treated with DA alone, only 1 had marginally reduced sensitivity. From analysis of sequences encoding the principal functional domains of the PML and RAR portions of PML-RAR, we found missense mutations in relapse specimens from 3 of 12 RA-treated patients and 0 of 8 DA-treated patients. All 3 mutations were located in the ligand binding domain (LBD) of the RAR region of PML-RAR. Relative to normal RAR1, the mutations were Leu290Val, Arg394Trp, and Met413Thr. All pretreatment analyses were normal except for a C to T base change in the 3′-untranslated (UT) region of 1 patient that was also present after relapse from DA therapy. No mutations were detected in the corresponding sequences of the normal RAR or PML (partial) alleles. Minor additional PML-RAR isoforms encoding truncated PML proteins were detected in 2 cases. We conclude that APL cellular resistance occurs with high incidence after relapse from RA + DA therapy administered in a nonconcurrent manner and that mutations in the RAR region of the PML-RAR gene are present in and likely mechanistically involved in RA resistance in a subset of these cases.

© 1998 by The American Society of Hematology.

Leukemic Cellular Retinoic Acid Resistance and Missense Mutations in the PML-RAR Fusion Gene After Relapse of Acute Promyelocytic Leukemia From Treatment With All-trans Retinoic Acid and Intensive Chemotherapy

This study evaluated whether relapse of acute promyelocytic leukemia (APL) patients from clinical remissions achieved and/or maintained with all-trans retinoic acid (RA) in combination with intensive chemotherapy is associated with leukemic cellular resistance to RA and with alterations in the PML-RAR fusion gene. We studied matched pretreatment and relapse specimens from 12 patients who received variable amounts of RA, primarily in nonconcurrent combination with daunorubicin and cytarabine (DA) on Eastern Cooperative Oncology Group (ECOG) protocol E2491, and from 8 patients who received DA only on protocol E2491. Of 10 RA-treated patients evaluable for a change in APL cell sensitivity to RA-induced differentiation in vitro, 8 showed diminished sensitivity at relapse, whereas, of 6 evaluable patients treated with DA alone, only 1 had marginally reduced sensitivity. From analysis of sequences encoding the principal functional domains of the PML and RAR portions of PML-RAR, we found missense mutations in relapse specimens from 3 of 12 RA-treated patients and 0 of 8 DA-treated patients. All 3 mutations were located in the ligand binding domain (LBD) of the RAR region of PML-RAR. Relative to normal RAR1, the mutations were Leu290Val, Arg394Trp, and Met413Thr. All pretreatment analyses were normal except for a C to T base change in the 3′-untranslated (UT) region of 1 patient that was also present after relapse from DA therapy. No mutations were detected in the corresponding sequences of the normal RAR or PML (partial) alleles. Minor additional PML-RAR isoforms encoding truncated PML proteins were detected in 2 cases. We conclude that APL cellular resistance occurs with high incidence after relapse from RA + DA therapy administered in a nonconcurrent manner and that mutations in the RAR region of the PML-RAR gene are present in and likely mechanistically involved in RA resistance in a subset of these cases.

© 1998 by The American Society of Hematology.

Early Detection of Relapse by Prospective Reverse Transcriptase-Polymerase Chain Reaction Analysis of the PML/RARα Fusion Gene in Patients With Acute Promyelocytic Leukemia Enrolled in the GIMEMA-AIEOP Multicenter “AIDA” Trial

Although the majority of patients with acute promyelocytic leukemia (APL) are potentially cured by treatments combining all-trans retinoic acid (ATRA) and chemotherapy (CHT), a sizable proportion (around 30%) will relapse during follow-up. Retrospective molecular monitoring studies using reverse transcriptase-polymerase chain reaction (RT-PCR) for the specific PML/RARα fusion gene, have shown that a positive test usually precedes the occurrence of hematologic relapse. Prospective RT-PCR analyses were performed since 1993 at diagnosis and at preestablished time intervals during follow-up in bone marrow (BM) samples of 163 patients with PML/RARα+ APL enrolled in the multicenter Gruppo Italiano Malattie Ematologiche Maligne dell' Adulto (GIMEMA) trial AIDA (All-trans retinoic acid plus Idarubicin). Treatment consisted of ATRA and idarubicin for induction followed by three polychemotherapy courses as consolidation. The sensitivity level of the RT-PCR assay for PML/RARα, as assessed by serial dilution experiments, was 10−4. All patients were in hematologic remission and tested PCR− at the end of consolidation. Of 21 who converted to PCR-positive thereafter, 20 underwent hematologic relapse at a median time of 3 months (range, 1 to 14) from the first PCR+ result. Seventeen of these 21 (81%) PCR+ conversions were recorded within the first 6 months postconsolidation. Of 142 who tested persistently PCR− in ≥2 tests after consolidation, 8 had hematologic relapse and 134 remained in complete remission (CR) after a median follow-up of 18 months (range, 6 to 38) postconsolidation. Using a time-dependent Cox model, the relative risk of hematologic relapse of patients who converted to PCR+ was 31.8 (confidence limits 95%, 12.9 to 78.3). Our results indicate that conversion to PCR positivity for PML/RARα during remission is highly predictive of subsequent hematologic relapse and highlight the prognostic value of stringent molecular monitoring during the early postconsolidation phase in APL. As a result of the present study, salvage treatment in patients enrolled in the GIMEMA trial AIDA is now anticipated at the time of molecular relapse, defined as the conversion to PCR positivity in two successive BM samplings during follow-up.

© 1998 by The American Society of Hematology.

Early Detection of Relapse by Prospective Reverse Transcriptase-Polymerase Chain Reaction Analysis of the PML/RARα Fusion Gene in Patients With Acute Promyelocytic Leukemia Enrolled in the GIMEMA-AIEOP Multicenter “AIDA” Trial

Although the majority of patients with acute promyelocytic leukemia (APL) are potentially cured by treatments combining all-trans retinoic acid (ATRA) and chemotherapy (CHT), a sizable proportion (around 30%) will relapse during follow-up. Retrospective molecular monitoring studies using reverse transcriptase-polymerase chain reaction (RT-PCR) for the specific PML/RARα fusion gene, have shown that a positive test usually precedes the occurrence of hematologic relapse. Prospective RT-PCR analyses were performed since 1993 at diagnosis and at preestablished time intervals during follow-up in bone marrow (BM) samples of 163 patients with PML/RARα+ APL enrolled in the multicenter Gruppo Italiano Malattie Ematologiche Maligne dell' Adulto (GIMEMA) trial AIDA (All-trans retinoic acid plus Idarubicin). Treatment consisted of ATRA and idarubicin for induction followed by three polychemotherapy courses as consolidation. The sensitivity level of the RT-PCR assay for PML/RARα, as assessed by serial dilution experiments, was 10−4. All patients were in hematologic remission and tested PCR− at the end of consolidation. Of 21 who converted to PCR-positive thereafter, 20 underwent hematologic relapse at a median time of 3 months (range, 1 to 14) from the first PCR+ result. Seventeen of these 21 (81%) PCR+ conversions were recorded within the first 6 months postconsolidation. Of 142 who tested persistently PCR− in ≥2 tests after consolidation, 8 had hematologic relapse and 134 remained in complete remission (CR) after a median follow-up of 18 months (range, 6 to 38) postconsolidation. Using a time-dependent Cox model, the relative risk of hematologic relapse of patients who converted to PCR+ was 31.8 (confidence limits 95%, 12.9 to 78.3). Our results indicate that conversion to PCR positivity for PML/RARα during remission is highly predictive of subsequent hematologic relapse and highlight the prognostic value of stringent molecular monitoring during the early postconsolidation phase in APL. As a result of the present study, salvage treatment in patients enrolled in the GIMEMA trial AIDA is now anticipated at the time of molecular relapse, defined as the conversion to PCR positivity in two successive BM samplings during follow-up.

© 1998 by The American Society of Hematology.

Induction of Differentiation in Acute Promyelocytic Leukemia Cells by 9-cis Retinoic Acid α-Tocopherol Ester (9-cisTretinoin Tocoferil)

Acute promyelocytic leukemia (APL) has a specific genetic rearrangement between the retinoic acid receptor (RAR)-α gene and the pml nuclear protein gene. All-trans retinoic acid (ATRA) induces granulocytic differentiation of APL-derived cells and is used to treat APL patients. However, ATRA interacts with normal cells with RAR throughout the entire body, and when used at high doses or over a long duration, it induces several adverse effects. The development of drugs that selectively act on APL cells may contribute to increasing the therapeutic efficacy of APL treatment as well as elucidating the mechanisms of response to ATRA. In this study, 9-cis retinoic acid α-tocopherol ester (9CTT) inhibited the proliferation of APL-derived NB4 and HT93 cells and induced differentiation markers, such as granulocytic maturation, nitroblue tetrazolium reduction, and CD11b expression, in these cells. The effects of 9CTT on non-APL cells, including HL-60 and U937 cells, were much weaker than those on APL cells, and tretinoin tocoferil (TT), which is an α-tocopherol ester of ATRA, did not induce the differentiation of APL cells as effectively as 9CTT. The differentiation-inducing effects of 9CTT were inhibited by RAR antagonists. 9CTT and TT similarly induced the transactivating activity of RARs, but were not effective on RXRs. 9CTT downregulated the expression of PML/RAR-α protein more effectively than TT, which suggests that it may be involved in the selectivity of 9CTT against APL cells. Interestingly, 9CTT enhanced the differentiation of APL cells induced by ATRA, 9-cis retinoic acid, and synthetic retinobenzoic acids. Combined with 1α,25-dihydroxyvitamin D3 (VD3), 9CTT also more than additively induced the differentiation of APL cells. Thus, 9CTT, alone or in combination with other retinoids or VD3, may be useful for the treatment of APL.

Induction of Differentiation in Acute Promyelocytic Leukemia Cells by 9-cis Retinoic Acid α-Tocopherol Ester (9-cisTretinoin Tocoferil)

Acute promyelocytic leukemia (APL) has a specific genetic rearrangement between the retinoic acid receptor (RAR)-α gene and the pml nuclear protein gene. All-trans retinoic acid (ATRA) induces granulocytic differentiation of APL-derived cells and is used to treat APL patients. However, ATRA interacts with normal cells with RAR throughout the entire body, and when used at high doses or over a long duration, it induces several adverse effects. The development of drugs that selectively act on APL cells may contribute to increasing the therapeutic efficacy of APL treatment as well as elucidating the mechanisms of response to ATRA. In this study, 9-cis retinoic acid α-tocopherol ester (9CTT) inhibited the proliferation of APL-derived NB4 and HT93 cells and induced differentiation markers, such as granulocytic maturation, nitroblue tetrazolium reduction, and CD11b expression, in these cells. The effects of 9CTT on non-APL cells, including HL-60 and U937 cells, were much weaker than those on APL cells, and tretinoin tocoferil (TT), which is an α-tocopherol ester of ATRA, did not induce the differentiation of APL cells as effectively as 9CTT. The differentiation-inducing effects of 9CTT were inhibited by RAR antagonists. 9CTT and TT similarly induced the transactivating activity of RARs, but were not effective on RXRs. 9CTT downregulated the expression of PML/RAR-α protein more effectively than TT, which suggests that it may be involved in the selectivity of 9CTT against APL cells. Interestingly, 9CTT enhanced the differentiation of APL cells induced by ATRA, 9-cis retinoic acid, and synthetic retinobenzoic acids. Combined with 1α,25-dihydroxyvitamin D3 (VD3), 9CTT also more than additively induced the differentiation of APL cells. Thus, 9CTT, alone or in combination with other retinoids or VD3, may be useful for the treatment of APL.

Constitutive Expression of the Promyelocytic Leukemia–Associated Oncogene PML-RARα in TF1 Cells: Isoform-Specific and Retinoic Acid–Dependent Effects on Growth, bcl-2 Expression, and Apoptosis

Two major isoforms of PML-RARα are associated with (15;17)-positive acute promyelocytic leukemia (APL); however, functional differences between these isoforms have been difficult to define, and the molecular mechanism by which each isoform contributes to the pathogenesis of APL is not fully understood. To address these issues, the ‘short’ (S) and ‘long’ (L) isoforms of PML-RARα were constitutively expressed in the factor-dependent human erythroleukemia cell line, TF1. Expression of the L, but not the S, isoform inhibited growth of these cells in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). In the absence of GM-CSF, the S isoform partially protected against apoptosis, while the L isoform accelerated cell death. Treatment with all-trans retinoic acid (ATRA) inhibited cell growth and caused apoptosis only in PML-RARα–expressing cells, and these effects of ATRA were more marked in cells expressing the L isoform. ATRA treatment also led to downregulation of bcl-2 and endogenous RARα in PML-RARα–expressing cells, but had little effect on the level of exogenously expressed PML-RARα. We conclude that (1) subtle differences exist in the biologic activities of the L and S isoforms of PML-RARα, and (2) both isoforms are capable of transducing an ATRA-mediated signal that leads to downregulation of bcl-2 and induction of programmed cell death.

Constitutive Expression of the Promyelocytic Leukemia–Associated Oncogene PML-RARα in TF1 Cells: Isoform-Specific and Retinoic Acid–Dependent Effects on Growth, bcl-2 Expression, and Apoptosis

Two major isoforms of PML-RARα are associated with (15;17)-positive acute promyelocytic leukemia (APL); however, functional differences between these isoforms have been difficult to define, and the molecular mechanism by which each isoform contributes to the pathogenesis of APL is not fully understood. To address these issues, the ‘short’ (S) and ‘long’ (L) isoforms of PML-RARα were constitutively expressed in the factor-dependent human erythroleukemia cell line, TF1. Expression of the L, but not the S, isoform inhibited growth of these cells in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). In the absence of GM-CSF, the S isoform partially protected against apoptosis, while the L isoform accelerated cell death. Treatment with all-trans retinoic acid (ATRA) inhibited cell growth and caused apoptosis only in PML-RARα–expressing cells, and these effects of ATRA were more marked in cells expressing the L isoform. ATRA treatment also led to downregulation of bcl-2 and endogenous RARα in PML-RARα–expressing cells, but had little effect on the level of exogenously expressed PML-RARα. We conclude that (1) subtle differences exist in the biologic activities of the L and S isoforms of PML-RARα, and (2) both isoforms are capable of transducing an ATRA-mediated signal that leads to downregulation of bcl-2 and induction of programmed cell death.

Retinoic acid syndrome. Recognition, prevention and management

The introduction of treatment with tretinoin (all-trans retinoic acid) and its combination with antineoplastic therapy has improved the outcome of acute promyelocytic leukaemia (APL). Retinoic acid syndrome is the major adverse effect of tretinoin and it occurs in about 25% of treated APL patients in the absence of prophylactic measures and is often fatal. Generally, the retinoic acid syndrome is associated with increasing leucocyte counts and is probably caused by the release of several cytokines by maturing blast cells. The retinoic acid syndrome gives a clinical picture of bodyweight gain, respiratory distress, serous effusions and cardiac and renal failure. Adequate prophylaxis, based on the addition to tretinoin of dexamethasone and also, according to most authors, antineoplastic therapy (in case of rapidly increasing leucocyte counts) has decreased the incidence of retinoic acid syndrome to about 15%. Most importantly, these measures have reduced its mortality to about 1% of all treated patients.

Characterization and Use of an Antibody Detecting the CBFβ-SMMHC Fusion Protein in inv(16)/t(16;16)-Associated Acute Myeloid Leukemias

The inv(16)(p13q22) and t(16;16)(p13;q22) cytogenetic abnormalities occur commonly in acute myeloid leukemia (AML), typically associated with French-American-British (FAB) AML-M4Eo subtype. Reverse transcriptase-polymerase chain reaction (RT-PCR) techniques have been recently developed to detect the presence of several variants of the resultant CBFB-MYH11 fusion gene that encodes a CBFβ-smooth muscle myosin heavy chain (SMMHC) fusion protein. We have now determined the clinical use of a polyclonal antibody [anti-inv(16) Ab] directed against a junctional epitope of the most common type of CBFβ-SMMHC fusion protein (type A), which is present in 90% of inv(16)/t(16;16) AML cases. Using flow cytometry, reproducible methods were developed for detection of CBFβ-SMMHC proteins in permeabilized cells; flow cytometric results were then correlated with cytogenetics and RT-PCR detection methods. In an analysis of 42 leukemia cases with various cytogenetic abnormalities and several normal controls, the anti-inv(16) Ab specifically detected all 23 cases that were cytogenetically positive for inv(16) or t(16;16), including a single AML case that was RT-PCR–negative. In addition to detecting all type A fusions, the anti-inv(16) Ab also unexpectedly identified the type C and type D CBFβ-SMMHC fusion proteins. Molecular characterization of one RT-PCR–positive and Ab-positive t(16;16) case with a non-type A product showed a novel previously unreported CBFB-MYH11 fusion (CBFB nt 455-MYH11 nt 1893). Flow cytometric results were analyzed using the Kolmogorov-Smirnov statistic D-value and the median value for positive samples was 0.65 (range, 0.35 to 0.77) versus 0.07 (range, −0.21 to 0.18) in the negative group (P < .0001). The overall concordance between cytogenetics and RT-PCR was 97%, whereas the concordance between flow cytometry and cytogenetics was 100%. Thus, using the anti-inv(16) Ab, all cytogenetically positive and RT-PCR–positive AML cases with inv(16) or t(16;16) could be rapidly identified. This study demonstrates the use of this antibody as an investigational tool in inv(16)/t(16;16) AML and suggests that the development of such reagents may have potential clinical diagnostic use.

Characterization and Use of an Antibody Detecting the CBFβ-SMMHC Fusion Protein in inv(16)/t(16;16)-Associated Acute Myeloid Leukemias

The inv(16)(p13q22) and t(16;16)(p13;q22) cytogenetic abnormalities occur commonly in acute myeloid leukemia (AML), typically associated with French-American-British (FAB) AML-M4Eo subtype. Reverse transcriptase-polymerase chain reaction (RT-PCR) techniques have been recently developed to detect the presence of several variants of the resultant CBFB-MYH11 fusion gene that encodes a CBFβ-smooth muscle myosin heavy chain (SMMHC) fusion protein. We have now determined the clinical use of a polyclonal antibody [anti-inv(16) Ab] directed against a junctional epitope of the most common type of CBFβ-SMMHC fusion protein (type A), which is present in 90% of inv(16)/t(16;16) AML cases. Using flow cytometry, reproducible methods were developed for detection of CBFβ-SMMHC proteins in permeabilized cells; flow cytometric results were then correlated with cytogenetics and RT-PCR detection methods. In an analysis of 42 leukemia cases with various cytogenetic abnormalities and several normal controls, the anti-inv(16) Ab specifically detected all 23 cases that were cytogenetically positive for inv(16) or t(16;16), including a single AML case that was RT-PCR–negative. In addition to detecting all type A fusions, the anti-inv(16) Ab also unexpectedly identified the type C and type D CBFβ-SMMHC fusion proteins. Molecular characterization of one RT-PCR–positive and Ab-positive t(16;16) case with a non-type A product showed a novel previously unreported CBFB-MYH11 fusion (CBFB nt 455-MYH11 nt 1893). Flow cytometric results were analyzed using the Kolmogorov-Smirnov statistic D-value and the median value for positive samples was 0.65 (range, 0.35 to 0.77) versus 0.07 (range, −0.21 to 0.18) in the negative group (P < .0001). The overall concordance between cytogenetics and RT-PCR was 97%, whereas the concordance between flow cytometry and cytogenetics was 100%. Thus, using the anti-inv(16) Ab, all cytogenetically positive and RT-PCR–positive AML cases with inv(16) or t(16;16) could be rapidly identified. This study demonstrates the use of this antibody as an investigational tool in inv(16)/t(16;16) AML and suggests that the development of such reagents may have potential clinical diagnostic use.

Molecular genetics of childhood leukemias

PURPOSE

This review summarizes the molecular genetics of childhood leukemias, with emphasis on pathogenesis and clinical applications.

DESIGN

We first describe the most common genetic events that occur in pediatric acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and chronic myeloid leukemia (CML). We then illustrate how these molecular alterations may be used to alter therapy.

RESULTS

In childhood ALL, the TEL-AML1 fusion and hyperdiploidy are both associated with excellent treatment outcomes and therefore identify patients who may be candidates for less intensive therapy. In contrast, MLL gene rearrangements and the BCR-ABL fusion confer a poor prognosis; these patients may be best treated by allogeneic bone marrow transplantation in first remission.

CONCLUSIONS

Although clinical features are important prognostic indicators, genetic alterations of leukemic blasts may be better predictors of outcome for acute leukemia patients. We therefore favor risk-adapted therapy based on classification schemes that incorporate both genetic and clinical features.