Collaborative Efforts Driving Progress in Pediatric Acute Myeloid Leukemia

Diagnosis, treatment, response monitoring, and outcome of pediatric acute myeloid leukemia (AML) have made enormous progress during the past decades. Because AML is a rare type of childhood cancer, with an incidence of approximately seven occurrences per 1 million children annually, national and international collaborative efforts have evolved. This overview describes these efforts and includes a summary of the history and contributions of each of the main collaborative pediatric AML groups worldwide. The focus is on translational and clinical research, which includes past, current, and future clinical trials. Separate sections concern acute promyelocytic leukemia, myeloid leukemia of Down syndrome, and relapsed AML. A plethora of novel antileukemic agents that have emerged, including new classes of drugs, are summarized as well. Finally, an important aspect of the treatment of pediatric AML--supportive care--and late effects are discussed. The future is bright, with a wide range of emerging innovative therapies and with more and more international collaboration that ultimately aim to cure all children with AML, with fewer adverse effects and without late effects.

Mutations in KIT and RAS are frequent events in pediatric core-binding factor acute myeloid leukemia

Activating mutations in RAS and receptor tyrosine kinases such as KIT and FLT3 are hypothesized to cooperate with chimeric transcription factors in the pathogenesis of acute myeloid leukemia (AML). To test this hypothesis, we genotyped 150 pediatric AML samples for mutations in KIT (exons 8, 17), NRAS and KRAS (exons 1, 2) and FLT3/ITD. This is the largest cohort of pediatric AML patients reported thus far screened for all four mutations. Of the children with AML, 40% had a mutation in KIT (11.3%), RAS (18%) or FLT3/ITD (11.1%), and 70% of cases of core-binding factor (CBF) leukemia were associated with a mutation of KIT or RAS. Mutations in RAS or FLT3/ITD were frequently found in association with a normal karyotype. Patients with a FLT3/ITD mutation had a significantly worse clinical outcome. However, the presence of a KIT or RAS mutation did not significantly influence clinical outcome. We demonstrate that KIT exon 8 mutations result in constitutive ligand-independent kinase activation that can be inhibited by clinically relevant concentrations of imatinib. Our results demonstrate that abnormalities of signal transduction pathways are frequent in pediatric AML. Future clinical studies are needed to determine whether selective targeting of these abnormalities will improve treatment results.

Early Deaths and Treatment-Related Mortality in Children Undergoing Therapy for Acute Myeloid Leukemia: Analysis of the Multicenter Clinical Trials AML-BFM 93 and AML-BFM 98

Purpose

The rates of early death (ED) and treatment-related mortality (TRM) are unacceptably high in children undergoing intensive chemotherapy for acute myeloid leukemia (AML). Better strategies of supportive care might help to improve overall survival in these children.

Patients and Methods

In a retrospective study, we analyzed incidence, clinical features, and risk factors for lethal complications of 901 children enrolled onto the multicenter trials Acute Myeloid Leukemia-Berlin-Frankfurt-Muenster (AML-BFM) 93 and AML-BFM 98.

Results

One hundred four patients (11.5%) enrolled onto the clinical trials AML-BFM 93 and AML-BFM 98 died shortly after diagnosis or as a result of treatment-related complications. Thirty-two patients (3.5%) died before (six patients) or during (26 patients) the first 14 days of treatment, mainly as a result of bleeding or leukostasis. Low performance status, hyperleukocytosis, and French-American-British type M5 were the main risk factors for a lethal event before day 15. After day 15, the predominant causes of death were complications caused by infections, particularly bacterial and fungal infections. The incidence of lethal infections was highest during induction therapy and decreased thereafter. When comparing both clinical trials, significantly fewer patients died within the first 6 weeks in AML-BFM 98 than in AML-BFM 93 (14 [3.5%] of 430 patients v 35 [7.4%] of 471 patients; P = .01).

Conclusion

To reduce the high incidence of ED and TRM in children with AML, early diagnosis and adequate treatment of complications are needed. Children with AML should be treated in specialized pediatric cancer centers only. Prophylactic and therapeutic regimens for better treatment management of bleeding disorders and infectious complications have to be assessed in future trials to ultimately improve overall survival in children with AML.

Prognostic Impact of Specific Chromosomal Aberrations in a Large Group of Pediatric Patients With Acute Myeloid Leukemia Treated Uniformly According to Trial AML-BFM 98

Purpose

Because cytogenetic data are essential for risk stratification of childhood acute myeloid leukemia (AML), the impact of chromosomal aberrations is crucial.

Patients and Methods

Data of a large group of patients younger than 18 years treated according to study AML–Berlin-Frankfurt-Münster (BFM) 98 (n = 454), including their cytogenetics, were analyzed.

Results

The favorable outcome in the subgroups of patients with t(8;21), inv(16), and t(15;17), with an overall survival of 91% (SE, 4%), 92% (SE, 6%), and 87% (SE, 5%), respectively, was confirmed. Within this group, the 5-year probability of event-free survival (pEFS) of all 17 children with t(8;21) and additional aberrations apart from del(9q) or −X/−Y was 100%. As expected, the cytogenetic finding of a complex karyotype (n = 35; pEFS, 33%; SE, 8%) or a monosomy 7 (n = 12; pEFS, 17%; SE, 11%) was associated with a poor outcome. Compared with remaining patients with cytogenetic data (pEFS, 48%; SE, 2%), prognosis in patients with an MLL rearrangement (n = 91) was inferior (pEFS, 34%; SE, 5%; P = .0005). Particularly, children with t(9;11) and additional aberrations (n = 13; pEFS, 31%; SE, 14%) and MLL rearrangements other than t(9;11) and t(11;19) (n = 41; pEFS, 24%; SE, 7%) had an unfavorable outcome. Nine patients with aberrations in 12p showed an adverse prognosis (pEFS, 11%; SE, 10%). The outcome of patients with aberrations of chromosome 5 (n = 13) was better than expected (pEFS, 50%; SE, 13%).

Conclusion

Because the prognostic value of rare recurrent chromosomal aberrations still has to be elucidated, these data will contribute to future risk stratification for the treatment of pediatric AML.

FLT3 internal tandem duplication in 234 children with acute myeloid leukemia: prognostic significance and relation to cellular drug resistance

FLT3 is a receptor tyrosine kinase involved in the proliferation and differentiation of hematopoietic stem cells. FLT3 internal tandem duplications (FLT3/ITDs) are reported in acute myeloid leukemia (AML) and predict poor clinical outcome. We found FLT3/ITDs in 11.5% of 234 children with de novo AML. FLT3/ITD-positive patients were significantly older and had higher percentages of normal cytogenetic findings or French-American-British (FAB) classification M1/M2 and lower percentages of 11q23 abnormalities or FAB M5. FLT3/ITD-positive patients had lower remission induction rates (70% vs 88%; P =.01) and lower 5-year probability rates of event-free survival (pEF) (29% vs 46%; P =.0046) and overall survival (32% vs 58%; P =.037). Patients with high ratios (higher than the median) between mutant and wild-type FLT3 had significantly worse 2-year EFS rates than FLT3/ITD-negative patients (pEFS 20% vs 61%; P =.037), whereas patients with ratios lower than the median did not (pEFS 44% vs 61%; P =.26). FLT3/ITD was the strongest independent predictor for pEFS, with an increase in relative risk for an event of 1.92 (P =.01). Using an MTT (methyl-thiazol-tetrazolium)-based assay, we studied cellular drug resistance on 15 FLT3/ITD-positive and 125 FLT3/ITD-negative AML samples, but we found no differences in cellular drug resistance that could explain the poor outcomes in FLT3/ITD-positive patients. We conclude that FLT3/ITD is less common in pediatric than in adult AML. FLT3/ITD is a strong and independent adverse prognostic factor, and high ratios between mutant and WT-FLT3 further compromise prognosis. However, poor outcomes in FLT3/ITD-positive patients could not be attributed to increased in vitro cellular drug resistance.

Improved outcome in pediatric relapsed acute myeloid leukemia: results of a randomized trial on liposomal daunorubicin by the International BFM Study Group

PURPOSE

In pediatric relapsed acute myeloid leukemia (AML), optimal reinduction therapy is unknown. Studies suggest that liposomal daunorubicin (DNX; DaunoXome; Galen, Craigavon, United Kingdom) is effective and less cardiotoxic, which is important in this setting. These considerations led to a randomized phase III study by the International Berlin-Frankfurt-Münster Study Group.

PATIENTS AND METHODS

Patients with relapsed or primary refractory non-French-American-British type M3 AML who were younger than 21 years of age were eligible. Patients were randomly assigned to fludarabine, cytarabine, and granulocyte colony-stimulating factor (FLAG) or to FLAG plus DNX in the first reinduction course. The primary end point was status of the bone marrow (BM) sampled shortly before the second course of chemotherapy (the day 28 BM). Data are presented according to intention-to-treat for all 394 randomly assigned patients (median follow-up, 4.0 years).

RESULTS

The complete remission (CR) rate was 64%, and the 4-year probability of survival (pOS) was 38% (SE, 3%). The day 28 BM status (available in 359 patients) was good (≤ 20% leukemic blasts) in 80% of patients randomly assigned to FLAG/DNX and 70% for patients randomly assigned to FLAG (P = .04). Concerning secondary end points, the CR rate was 69% with FLAG/DNX and 59% with FLAG (P = .07), but overall survival was similar. However, core-binding factor (CBF) AML treated with FLAG/DNX resulted in pOS of 82% versus 58% with FLAG (P = .04). Grade 3 to 4 toxicity was essentially similar in both groups.

CONCLUSION

DNX added to FLAG improves early treatment response in pediatric relapsed AML. Overall long-term survival was similar, but CBF-AML showed an improved survival with FLAG/DNX. International collaboration proved feasible and resulted in the best outcome for pediatric relapsed AML reported thus far.

Infectious complications in pediatric acute myeloid leukemia: analysis of the prospective multi-institutional clinical trial AML-BFM 93

Infections still remain a major cause of therapy-associated morbidity and mortality in children with acute myeloid leukemia (AML). To improve supportive care measurements, detailed information on frequency and characteristic features of infectious complications is needed. We retrospectively analyzed the medical charts of 304 children, treated in 30 hospitals according to the multi-institutional clinical trial AML-BFM 93. Overall, 855 infectious complications occurred in 304 patients (fever without identifiable source (n=523; 61.2%), clinically (n=57; 6.7%) and microbiologically documented infections (n=275; 32.1%)). Neutropenia was present in 74.1% of the infectious episodes. In all, 20 patients died of infection-associated complications (15/276 (5.4%) patients without and 5/28 (17.9%) with Down syndrome), most of them during early induction therapy (n=11). Blood stream infections occurred in 228 episodes (Gram-positive (n=202) and Gram-negative (n=42) pathogens). Invasive fungal infection was probable or proven in 15 patients. In 113 out of the 855 infectious episodes (13.3%), pneumonia was radiologically diagnosed. Better strategies of supportive care might help to improve overall survival in children undergoing chemotherapy for AML. Therefore, children with AML should be treated in specialized pediatric centers, and there should be a very low threshold to readmit patients, in particular patients with pulmonary symptoms.

Treatment strategies and long-term results in paediatric patients treated in four consecutive AML-BFM trials

A total of 1111 children with acute myeloblastic leukaemia (AML) were treated in four consecutive Berlin-Frankfurt-Münster (BFM) studies from 1978 to 1998. The first cooperative trial AML-BFM 78 established intensive chemotherapy with seven drugs, CNS irradiation and 2-year maintenance, achieving a long-term survival (overall survival (OS)) of 40%. Induction intensification in AML-BFM 83 resulted in significant improvement of disease-free survival (DFS). The risk of haemorrhage, especially in children with hyperleukocytosis, proved the high relevance of supportive care. In AML-BFM 87, the benefit of CNS irradiation in preventing CNS/systemic relapses was demonstrated. In AML-BFM 93, the introduction of idarubicin during first induction followed by intensification with HAM increased the 5-year EFS, DFS and OS to 50+/-2, 61+/-3 and 57+/-2%, respectively. Stem cell transplantation (SCT), as applied in high-risk patients with a matched related donor, did not significantly improve the outcome compared to chemotherapy alone. In spite of treatment intensification, the therapy-related death rate decreased from trial to trial, mainly during induction. The future aim is to reduce long-term sequelae, especially cardiotoxicity, by administration of less cardiotoxic drugs, and toxicity of SCT by risk-adapted indications. The AML-BFM studies performed in three European countries with >70 cooperating centres have significantly improved the outcome in AML children; nevertheless, increasing experience with these intensive treatment regimens is of fundamental importance to reduce fatal complications.

Improved treatment results in high-risk pediatric acute myeloid leukemia patients after intensification with high-dose cytarabine and mitoxantrone: results of Study Acute Myeloid Leukemia-Berlin-Frankfurt-Münster 93

PURPOSE

To improve outcome in high-risk patients, high-dose cytarabine and mitoxantrone (HAM) was introduced into the treatment of children with acute myelogenous leukemia (AML) in study AML-BFM 93. Patients were randomized to HAM as either the second or third therapy block, for the purpose of evaluation of efficacy and toxicity.

PATIENTS AND METHODS

A total of 471 children with de novo AML were entered onto the trial; 161 were at standard risk and 310 were at high risk. After the randomized induction (daunorubicin v idarubicin), further therapy, with the exception of HAM, was identical in the two risk groups and also comparable to that in study Acute Myeloid Leukemia-Berlin-Frankfurt-Münster (AML-BFM) 87.

RESULTS

Overall, 387 (82%) of 471 patients achieved complete remission, and 5-year survival, event-free survival (EFS), and disease-free survival rates were 60%, 51%, and 62%, respectively. Idarubicin induction resulted in a significantly better blast cell reduction in the bone marrow on day 15. Estimated survival and probability of EFS were superior in study AML-BFM 93 compared with study AML-BFM 87 (P =.01, log-rank test). This improvement, however, was restricted to the 310 high-risk patients (remission rate and probability of 5-year EFS in study AML-BFM 93 v study AML-BFM 87: 78% v 68%, P =.007; and 44% v 31%, P =.01, log-rank test). Probability of 5-year EFS among standard-risk patients in study AML-BFM 93 was similar to that in study AML-BFM 87 (65% v 63%, P = not significant). Whether HAM was placed as the second or third therapy block was of minor importance. However, patients who received the less intensive daunorubicin treatment during induction benefited from early HAM.

CONCLUSION

Improved treatment results in children with high-risk AML in study AML-BFM 93 must be attributed mainly to the introduction of HAM.

Stability and prognostic influence of FLT3 mutations in paired initial and relapsed AML samples

In acute myeloid leukemia (AML), activating mutations in the fms-like tyrosine kinase 3 (FLT3) gene predict poor prognosis. We determined FLT3 internal tandem duplications (FLT3/ITD) and D835 point mutations in paired initial and relapse samples from 80 pediatric and adult AML patients. One D835 point mutation was found in an initial pediatric AML sample. Fms-like tyrosine kinase 3/ITDs were present in 21 initial and 22 relapse samples (26.3 and 27.5%, respectively). Interestingly, FLT3/ITD positivity was related to a significantly shorter time to relapse, most pronounced when the ITD-positive status was found at relapse (P<0.001). However, FLT3/ITD status changed between diagnosis and relapse in 14 cases. In four patients, the FLT3/ITD became undetectable at relapse in five patients FLT3/ITDs were only detected at relapse, and in five patients the length or number of FLT3/ITDs changed. Gain of FLT3/ITDs may suggest oligoclonality with selective outgrowth of the FLT3/ITD-positive clone, whereas losses may reflect ITDs in the more mature leukemic cells rather than in the leukemic stem cell, or, alternatively, that other genetic aberrations provided a greater selective advantage. Studying FLT3/ITD kinetics in minimal residual disease setting may provide some answers for the changes we observed. Fms-like tyrosine kinase 3/ITD is a relevant marker for prognosis, and remains an important target for therapeutic inhibition.

Less toxicity by optimizing chemotherapy, but not by addition of granulocyte colony-stimulating factor in children and adolescents with acute myeloid leukemia: results of AML-BFM 98

PURPOSE

To improve prognosis in children with acute myeloid leukemia (AML) by randomized comparisons of (1) two short consolidation cycles versus the Berlin-Frankfurt-Muenster (BFM) -type biphasic 6-week consolidation and (2) the prophylactic administration of granulocyte colony-stimulating factor (G-CSF) versus no G-CSF. Further, therapy for standard risk patients was intensified by addition of a second induction, HAM (high-dose cytarabine and mitoxantrone).

PATIENTS AND METHODS

Four hundred seventy-three patients younger than 18 years with de novo AML were enrolled in trial AML-BFM 98. Patients received five courses of intensive chemotherapy, cranial irradiation, and 1-year maintenance therapy.

RESULTS

Four hundred eighteen patients (88%) achieved remission. Compared with trial AML-BFM 93, early deaths decreased from 7.4 to 3.2% (P = .005), and 5-year overall survival increased from 58% to 62% (log-rank P = .03). Both types of consolidation therapy led to similar outcome (event-free survival, 51% v 50%), but in the two-cycle arm, treatment duration was shorter (median duration, 15 days), and treatment related mortality was lower (five v nine patients). G-CSF shortened neutropenia, but did not reduce the rate of severe infections. Intensification of induction therapy did not improve prognosis of standard-risk patients (event-free survival, 62% v 67%).

CONCLUSION

Overall results were improved by neither the administration of G-CSF nor by cycle therapy; however, the latter was easier to perform. Compared with study AML-BFM 93, therapy intensification with HAM in standard-risk patients did not result in improved prognosis. Future treatment designs have to balance intensification of treatment with higher toxicity, improve supportive care, and to consider alternative treatment strategies.

High expression levels of x-linked inhibitor of apoptosis protein and survivin correlate with poor overall survival in childhood de novo acute myeloid leukemia

PURPOSE

Apoptosis-related proteins are important molecules for predicting chemotherapy response and prognosis in adult acute myeloid leukemia (AML). However, data on the expression and prognostic impact of these molecules in childhood AML are rare.

EXPERIMENTAL DESIGN

Using flow cytometry and Western blot analysis, we, therefore, investigated 45 leukemic cell samples from children with de novo AML enrolled and treated within the German AML-BFM93 study for the expression of apoptosis-regulating proteins [CD95, Bcl-2, Bax, Bcl-xL, procaspase-3, X-linked inhibitor of apoptosis protein (XIAP), cellular inhibitor of apoptosis protein-1 (cIAP-1), survivin].

RESULTS

XIAP (P < 0.002) but no other apoptosis regulators showed maturation-dependent expression differences as determined by French-American-British (FAB) morphology with the highest expression levels observed within the immature M0/1 subtypes. XIAP (P < 0.01) and Bcl-xL (P < 0.01) expression was lower in patients with favorable rather than intermediate/poor cytogenetics. After a mean follow-up of 34 months, a shorter overall survival was associated with high expression levels of XIAP [30 (n = 10) versus 41 months (n = 34); P < 0.05] and survivin [27 (n = 10) versus 41 months (n = 34); P < 0.05].

CONCLUSIONS

We conclude that apoptosis-related molecules are associated with maturation stage, cytogenetic risk groups, and therapy outcome in childhood de novo AML. The observed association of XIAP with immature FAB types, intermediate/poor cytogenetics, and poor overall survival should be confirmed within prospective pediatric AML trials.

AML patients with Down syndrome have a high cure rate with AML-BFM therapy with reduced dose intensity

Despite improved prognosis in acute myelogenous leukaemia (AML) children with Down syndrome (DS), therapy-related toxicity remained a problem. We compared 67 DS patients from study AML-BFM 98 with 51 DS patients of the previous study AML-BFM 93, and the non-DS groups of both studies. Compared to non-DS patients, DS patients were treated with reduced anthracycline doses, without high-dose cytarabine/mitoxantrone and without cranial irradiation. AML-DS patients were in median 1.8 years old, and 102/118 (86%) showed the typical morphology of acute megakaryoblastic leukaemia. In study 93, seven DS patients did not receive AML-specific chemotherapy, and treatment modifications were more common. Results improved significantly for patients treated in study 98 with a 3-year survival of 91+/-4 vs 70+/-7% in study 93 (P=0.001). There were no differences in outcome concerning the age groups 0-<or=2 and 2-<or=4 years (event-free survival for treated patients 0-<or=2 years 83+/-4%, 2-<or=4 years 81+/-7%). The cumulative incidence of relapses was significantly lower in DS (7+/-3%) than in non-DS patients (28+/-7%). Therapy-related toxicity was generally lower in DS patients treated according to study 98. We conclude that a standardised and dose-reduced treatment schedule including the main components of AML treatment is advisable for AML children with DS.

Idarubicin improves blast cell clearance during induction therapy in children with AML: results of study AML-BFM 93. AML-BFM Study Group

In the randomized trial AML-BFM 93 we compared 60 mg/m2/day daunorubicin with 12 mg/m2/day idarubicin for 3 days each, combined with cytarabine and etoposide during induction. Results showed a significant better blast cell reduction in the bone marrow on day 15 in patients of the idarubicin arm (25 of 144 = 17% of patients with > or = 5% blasts compared to 46 of 149 = 31% of patients after daunorubicin, Pchi2 = 0.01). This was, however, mainly seen in high risk patients treated with idarubicin (19% vs 38%, Pchi2 = 0.007). Cardiotoxicity, WHO grade 1-3 shortening fraction reduction after induction occurred in 6% patients in both arms. Bone marrow toxicity differed slightly with a median recovery time of neutrophils >500/microl of 25 days (daunorubicin) compared to 27 days (idarubicin), P = 0.05. In the total group of patients probabilities of 5 years event-free survival and disease-free survival were similar for patients treated with daunorubicin or idarubicin (49% +/- 4% vs 55% +/- 4% and 57% +/- 4% vs 64% +/- 4%, P logrank 0.29 and 0.15, respectively). However, in patients presenting with more than 5% blasts on day 15 there was a trend for a better outcome after treatment with idarubicin (P logrank 0.06). Together with the early effect seen for high risk patients these results indicate a better efficacy of idarubicin than of daunorubicin during induction with a similar rate of toxicity.

Different drug sensitivity profiles of acute myeloid and lymphoblastic leukemia and normal peripheral blood mononuclear cells in children with and without Down syndrome

Children with Down syndrome (DS) have an increased risk for leukemia. The prognosis for DS acute myeloid leukemia (AML) is better than for non-DS AML, but the clinical outcome of DS acute lymphoblastic leukemia (ALL) is equal to that of non-DS ALL. Differences in prognosis may reflect differences in cellular drug resistance. In vitro drug resistance profiles were successfully investigated on leukemic cells from 13 patients with DS AML and 9 patients with DS ALL and were compared with reference data from 151 non-DS AML and 430 non-DS B-cell precursor (BCP) ALL. DS AML cells were significantly more sensitive to cytarabine (median, 12-fold), the anthracyclines (2-7-fold), mitoxantrone (9-fold), amsacrine (16-fold), etoposide (20-fold), 6-thioguanine (3-fold), busulfan (5-fold), vincristine (23-fold), and prednisolone (more than 1.1-fold), than non-DS AML cells. Compared with DS ALL, DS AML cells were significantly more sensitive to cytarabine only (21-fold). After short-term exposure to methotrexate, DS AML cells were 21-fold more resistant than non-DS AML cells, but no difference was observed after continuous exposure. DS ALL cells and non-DS BCP-ALL cells were equally sensitive to all drugs, including methotrexate. Normal peripheral blood mononuclear cells from DS and non-DS children without leukemia showed highly resistant drug profiles. It was concluded that the better prognosis of DS AML might, at least partially, be explained by a specific, relatively sensitive drug-resistance profile, reflecting the unique biology of this disease. (Blood. 2002;99:245-251)

Residual Disease Monitoring in Childhood Acute Myeloid Leukemia by Multiparameter Flow Cytometry: The MRD-AML-BFM Study Group

Purpose

Monitoring of residual disease (RD) by flow cytometry in childhood acute myeloid leukemia (AML) may predict outcome. However, the optimal time points for investigation, the best antibody combinations, and most importantly, the clinical impact of RD analysis remain unclear.

Patients and Methods

Five hundred forty-two specimens of 150 children enrolled in the AML-Berlin-Frankfurt-Muenster (BFM) 98 study were analyzed by four-color immunophenotyping at up to four predefined time points during treatment. For each of the 12 leukemia-associated immunophenotypes and time points, a threshold level based on a previous retrospective analysis of another cohort of children with AML and on control bone marrows was determined.

Results

Regarding all four time points, there is a statistically significant difference in the 3-year event-free survival (EFS) in those children presenting with immunologically detectable blasts at 3 or more time points. The levels at bone marrow puncture (BMP) 1 and BMP2 turned out to have the most significant predictive value for 3-year-EFS: 71% ± 6% versus 48% ± 9%, PLog-Rank = .029 and 70% ± 6% versus 50% ± 7%, PLog-Rank = .033), resulting in a more than two-fold risk of relapse. In a multivariate analysis, using a combined risk classification based on morphologically determined blasts at BMP1 and BMP2, French-American-British classification, and cytogenetics, the influence of immunologically determined RD was no longer statistically significant.

Conclusion

RD monitoring before second induction has the same predictive value as examining levels at four different time points during intensive chemotherapy. Compared with commonly defined risk factors in the AML-BFM studies, flow cytometry does not provide additional information for outcome prediction, but may be helpful to evaluate the remission status at day 28.

Definition of a standard-risk group in children with AML

To define paediatric AML patients with a favourable outcome in order to design a risk-adapted therapy, we analysed 489 children under 17 years of age treated similarly in studies AML-BFM 83 and 87. 369 patients (75.4%) achieved remission. Estimated probabilities of survival, event-free survival (EFS) and disease-free survival (DFS) at 5 years were 50% (SE 2%), 43% (SE 2%) and 58% (SE 3%), respectively. Multivariate analysis revealed bone marrow blasts on day 15, morphologically defined risk groups and hyperleucocytosis to be of prognostic value. EFS at 5 years estimated for patients with < or = 5% and >5% blasts on day 15 were 56% (SE 3%) v 27% (SE 4%); for the favourable morphological subgroups (M1/M2 with Auer rods, M3 and M4eo) it was 60% (SE 4%) compared with other patients (33%, SE 3%), P (Kaplan-Meier) = 0.0001 each. Hyperleucocytosis proved to be an independent prognostic factor, indicating a high risk, especially for early failure. The specific karyotypes t(8;21), t(15;17) and inv16 were closely related to the favourable morphology and outcome was in the same range. We conclude that for the definition of a standard-risk group a combination of morphological and response criteria may be sufficient. The standard-risk group defined by favourable morphology and a blast cell reduction on day 15 (not required for M3) comprises 31% of all patients, P survival, pEFS and pDFS at 5 years were 73% (SE 4%), 68% (SE 5%) and 76% (SE 4%), respectively.

The human equilibrative nucleoside transporter 1 mediates in vitro cytarabine sensitivity in childhood acute myeloid leukaemia

Cytarabine (ara-C) is the most effective agent for the treatment of acute myeloid leukaemia (AML). Aberrant expression of enzymes involved in the transport/metabolism of ara-C could explain drug resistance. We determined mRNA expression of these factors using quantitative-real-time-PCR in leukemic blasts from children diagnosed with de novo AML. Expression of the inactivating enzyme pyrimidine nucleotidase-I (PN-I) was 1.8-fold lower in FAB-M5 as compared to FAB-M1/2 (P=0.007). In vitro sensitivity to deoxynucleoside analogues was determined using the MTT-assay. Human equilibrative nucleoside transporter-1 (hENT1) mRNA expression and ara-C sensitivity were significantly correlated (r_p=−0.46; P=0.001), with three-fold lower hENT1 mRNA levels in resistant patients (P=0.003). hENT1 mRNA expression also seemed to correlate inversely with the LC₅₀ values of cladribine (r_p=−0.30; P=0.04), decitabine (r_p=−0.29; P=0.04) and gemcitabine (r_p=−0.33; P=0.02). Deoxycytidine kinase (dCK) and cytidine deaminase (CDA) mRNA expression seemed to correlate with in vitro sensitivity to gemcitabine (r_p=−0.31; P=0.03) and decitabine (r_p=0.33; P=0.03), respectively. The dCK/PN-I ratio correlated inversely with LC₅₀ values for gemcitabine (r_p=−0.45, P=0.001) and the dCK/CDA ratio seemed to correlate with LC₅₀ values for decitabine (r_p=−0.29; 0.04). In conclusion, decreased expression of hENT1, which transports ara-C across the cell membrane, appears to be a major factor in ara-C resistance in childhood AML.

Monosomy 7 and deletion 7q in children and adolescents with acute myeloid leukemia: an international retrospective study

Monosomy 7 (-7) and deletion 7q \del(7q)] are rare in childhood acute myeloid leukemia (AML). We retrospectively collected data on 258 children with AML or refractory anemia with excess blasts in transformation (RAEB-T) and -7 or del(7q) with or without other cytogenetic aberrations \+/- other]. Karyotypes included -7 (n = 90), -7 other (n = 82), del(7q) (n = 21), and del(7q) other (n = 65). Complete remission (CR) was achieved in fewer patients with -7 +/- other compared with del(7q) +/- other (61% versus 89%, P < .001). Overall, the 5-year survival rate was 39% (SE, 3%). Survival was superior in del(7q) +/- other compared with -7 +/- other (51% versus 30%, P < .01). Cytogenetic aberrations considered favorable in AML \t(8;21)(q22;q22), inv(16)(p13q22), t(15;17)(q22;q21), t(9;11)(p22;q23)] (n = 24) were strongly associated with del(7q) and a higher 5-year survival rate compared with del(7q) without favorable cytogenetics (75% versus 46%, P = .03). Patients with -7 and inv(3),-5/del(5q), or + 21 had a 5-year survival rate of 5%. Stem cell transplantation analyzed as a time-dependent variable had no impact on overall survival. However, patients not achieving CR had a 31% survival rate after stem cell transplantation. Childhood AML with chromosome 7 aberrations represents a heterogeneous group of disorders with additional cytogenetic aberrations having a major prognostic impact which should be reflected in future risk-group stratification.

Does cranial irradiation reduce the risk for bone marrow relapse in acute myelogenous leukemia? Unexpected results of the Childhood Acute Myelogenous Leukemia Study BFM-87

PURPOSE

One of the goals of study AMA-BFM-87 was to test prospectively in acute myelogenous leukemia (AML) patients if cranial irradiation could be replaced by late intensification therapy with high-dose cytarabine (Ara-C) and etoposide (VP-16).

PATIENTS AND METHODS

Patients with a low risk of CNS relapses (ie, no initial CNS disease, WBC count at diagnosis < or = 70.000/microL) were randomized for irradiation (group A, 31 patients). In 25 patients (group B), randomization was refused. As interim results showed no increase of CNS relapses in nonirradiated patients, prophylactic irradiation was discontinued after 2 1/2 years to prevent unnecessary CNS toxicity. Forty-four patients (group C) entered the study after randomization had been stopped.

RESULTS

In all patients with a low risk of CNS recurrences (n = 100), a significantly higher probability of relapse-free interval (pRFI) of 5 years was found in irradiated patients (pRFI = .78) compared with nonirradiated patients (pRFI = .41) (P = .007). Moreover, a slightly higher incidence of CNS relapses was observed in nonirradiated patients. Due to the small number of patients, this was not observed when randomized patients only were analyzed. In accordance with these findings, the favorable outcome of low-risk patients in the preceding study, AML-BFM-83 (pRFI > .80), could only be reproduced in study AML-BFM-87 in patients who had received cranial irradiation.

CONCLUSION

These results indicate that cranial irradiation should be an integral part of the treatment of all AML patients not undergoing bone marrow transplantation. Residual blasts in the CNS may escape systemic chemotherapy and lead to recurrence of the initial disease not only in the CNS, but also in the bone marrow.

Consequent and intensified relapse therapy improved survival in pediatric AML: results of relapse treatment in 379 patients of three consecutive AML-BFM trials

Relapse remains the major cause of treatment failure in pediatric acute myeloid leukemia (AML). We analyzed the clinical characteristics, treatment response to relapse treatment and overall survival (OS) of 379 children with AML relapse treated according to three consecutive frontline protocols of the AML-Berlin/Frankfurt/Muenster study group (AML-BFM-87/-93/-98). Of 313 treated patients with data on remission status, 198 children (63%) achieved a second complete remission (CR2). There were no significant differences in remission rates and OS for the intensive reinduction treatment schedules used. The 5-year OS rate was 23% for the total group and 29% for patients treated with curative intent. OS rates increased with study periods from 18 to 34% (P(log rank)=0.012), whereas the proportion of patients receiving only palliative treatment decreased from 23 to 11% (P(CMH)=0.005). Late relapse, no allogeneic stem cell transplantation (SCT) in CR1, age <10 years and favorable cytogenetics were independent favorable prognostic factors for survival. Achievement of CR2 was the most important prognostic factor (OS 44 vs 3%; P(log rank)<0.0001). Overall, one-third of children with relapsed AML can be cured today. SCT in CR2 is recommended for most patients, although its impact on CR2 is discussed.

Integrative analysis of type-I and type-II aberrations underscores the genetic heterogeneity of pediatric acute myeloid leukemia

BACKGROUND

Several studies of pediatric acute myeloid leukemia have described the various type-I or type-II aberrations and their relationship with clinical outcome. However, there has been no recent comprehensive overview of these genetic aberrations in one large pediatric acute myeloid leukemia cohort.

DESIGN AND METHODS

We studied the different genetic aberrations, their associations and their impact on prognosis in a large pediatric acute myeloid leukemia series (n=506). Karyotypes were studied, and hotspot regions of NPM1, CEPBA, MLL, WT1, FLT3, N-RAS, K-RAS, PTPN11 and KIT were screened for mutations of available samples. The mutational status of all type-I and type-II aberrations was available in 330 and 263 cases, respectively. Survival analysis was performed in a subset (n=385) treated on consecutive acute myeloid leukemia Berlin-Frankfurt-Munster Study Group and Dutch Childhood Oncology Group treatment protocols.

RESULTS

Genetic aberrations were associated with specific clinical characteristics, e.g. significantly higher diagnostic white blood cell counts in MLL-rearranged, WT1-mutated and FLT3-ITD-positive acute myeloid leukemia. Furthermore, there was a significant difference in the distribution of these aberrations between children below and above the age of two years. Non-random associations, e.g. KIT mutations with core-binding factor acute myeloid leukemia, and FLT3-ITD with t(15;17)(q22;q21), NPM1- and WT1-mutated acute myeloid leukemia, respectively, were observed. Multivariate analysis revealed a 'favorable karyotype', i.e. t(15;17)(q22;q21), t(8;21)(q22;q22) and inv(16)(p13q22)/t(16;16)(p13;q22). NPM1 and CEBPA double mutations were independent factors for favorable event-free survival. WT1 mutations combined with FLT3-ITD showed the worst outcome for 5-year overall survival (22±14%) and 5-year event-free survival (20±13%), although it was not an independent factor in multivariate analysis.

CONCLUSIONS

Integrative analysis of type-I and type-II aberrations provides an insight into the frequencies, non-random associations and prognostic impact of the various aberrations, reflecting the heterogeneity of pediatric acute myeloid leukemia. These aberrations are likely to guide the stratification of pediatric acute myeloid leukemia and may direct the development of targeted therapies.

Myelodysplastic syndrome, juvenile myelomonocytic leukemia, and acute myeloid leukemia associated with complete or partial monosomy 7. European Working Group on MDS in Childhood (EWOG-MDS)

We reviewed the clinical features, treatment, and outcome of 100 children with myelodysplastic syndrome (MDS), juvenile myelomonocytic leukemia (JMML), and acute myeloid leukemia (AML) associated with complete monosomy 7 (-7) or deletion of the long arm of chromosome 7 (7q-). Patients with therapy-induced disease were excluded. The morphologic diagnoses according to modified FAB criteria were: MDS in 72 (refractory anemia (RA) in 11, RA with excess of blasts (RAEB) in eight, RAEB in transformation (RAEB-T) in 10, JMML in 43), and AML in 28. The median age at presentation was 2.8 years (range 2 months to 15 years), being lowest in JMML (1.1 year). Loss of chromosome 7 as the sole cytogenetic abnormality was observed in 75% of those with MDS compared with 32% of those with AML. Predisposing conditions (including familial MDS/AML) were found in 20%. Three-year survival was 82% in RA, 63% in RAEB, 45% in JMML, 34% in AML, and 8% in RAEB-T. Children with -7 alone had a superior survival than those with other cytogenetic abnormalities: this was solely due to a better survival in MDS (3-year survival 56 vs 24%). The reverse was found in AML (3-year survival 13% in -7 alone vs 44% in other cytogenetic groups). Stable disease for several years was documented in more than half the patients with RA or RAEB. Patients with RA, RAEB or JMML treated with bone marrow transplantation (BMT) without prior chemotherapy had a 3-year survival of 73%. The morphologic diagnosis was the strongest prognostic factor. Only patients with a diagnosis of JMML fitted what has previously been referred to as the monosomy 7 syndrome. Our data give no support to the concept of monosomy 7 as a distinct syndrome.