Pediatric acute myeloid leukemia: international progress and future directions

Novel prognostic subgroups in childhood 11q23/MLL-rearranged acute myeloid leukemia: results of an international retrospective study

Translocations involving chromosome 11q23 frequently occur in pediatric acute myeloid leukemia (AML) and are associated with poor prognosis. In most cases, the MLL gene is involved, and more than 50 translocation partners have been described. Clinical outcome data of the 11q23-rearranged subgroups are scarce because most 11q23 series are too small for meaningful analysis of subgroups, although some studies suggest that patients with t(9;11)(p22;q23) have a more favorable prognosis. We retrospectively collected outcome data of 756 children with 11q23- or MLL-rearranged AML from 11 collaborative groups to identify differences in outcome based on translocation partners. All karyotypes were centrally reviewed before assigning patients to subgroups. The event-free survival of 11q23/MLL-rearranged pediatric AML at 5 years from diagnosis was 44% (+/- 5%), with large differences across subgroups (11% +/- 5% to 92% +/- 5%). Multivariate analysis identified the following subgroups as independent prognostic predictors: t(1;11)(q21;q23) (hazard ratio [HR] = 0.1, P = .004); t(6;11)(q27;q23) (HR = 2.2, P < .001); t(10;11)(p12;q23) (HR = 1.5, P = .005); and t(10;11)(p11.2;q23) (HR = 2.5, P = .005). We could not confirm the favorable prognosis of the t(9;11)(p22;q23) subgroup. We identified large differences in outcome within 11q23/MLL-rearranged pediatric AML and novel subgroups based on translocation partners that independently predict clinical outcome. Screening for these translocation partners is needed for accurate treatment stratification at diagnosis.

Clinical relevance of Wilms tumor 1 gene mutations in childhood acute myeloid leukemia

Wilms tumor 1 (WT1) mutations have recently been identified in approximately 10% of adult acute myeloid leukemia (AML) with normal cytogenetics (CN-AML) and are associated with poor outcome. Using array-based comparative genome hybridization in pediatric CN-AML samples, we detected a WT1 deletion in one sample. The other WT1 allele was mutated. This prompted us to further investigate the role of WT1 aberrations in childhood AML. Mutations were found in 35 of 298 (12%) diagnostic pediatric AML samples. In 19 of 35 (54%) samples, more than one WT1 aberration was found: 15 samples had 2 different mutations, 2 had a homozygous mutation, and 2 had a mutation plus a WT1 deletion. WT1 mutations clustered significantly in the CN-AML subgroup (22%; P < .001) and were associated with FLT3/ITD (43 vs 17%; P < .001). WT1 mutations conferred an independent poor prognostic significance (WT1 mutated vs wild-type patients: 5-year probability of overall survival [pOS] 35% vs 66%, P = .002; probability of event-free survival 22% vs 46%, P < .001; and cumulative incidence of relapse or regression 70% vs 44%, P < .001). Patients with both a WT1 mutation and a FLT3/ITD had a dismal prognosis (5-year pOS 21%). WT1 mutations occur at a significant rate in childhood AML and are a novel independent poor prognostic marker.

Treatment strategies for pediatric acute myeloid leukemia

Therapeutic strategies utilized in recently completed Phase III clinical trials in children with de novo acute myeloid leukemia have led to long-term disease-free survival in 50 - 60% of children. This review describes the contributions from early intensification of therapy and postremission intensification using highly myelosuppressive chemotherapy strategies and discusses the controversial roles of allogeneic bone marrow transplantation, maintenance therapy and CNS irradiation. Current strategies focusing on the identification of critical biologic features and measurements of early response to therapy allow for greatly improved risk group stratification. Future improvements in the treatment of children with acute myeloid leukemia will depend on a better understanding of the biology of the disease, targeted therapeutic approaches directed to specific biologic targets, selective use of allogeneic transplantation and innovative clinical trial designs that will allow for the testing of an increasing number of new agents in increasingly small numbers of patients in defined risk groups.

Combination of cladribine and cytarabine is effective for childhood acute myeloid leukemia: results of the St Jude AML97 trial

Because cladribine can increase cytarabine triphosphate levels, we tested a cladribine—cytarabine combination in the St. Jude AML97, trial in which this combination was administered before standard chemotherapy to 96 children with acute myeloid leukemia (AML) or myelodysplastic syndrome. Patients received a 5-day course of cladribine (9 mg/m²/dose) and cytarabine either as daily 2-hour infusions (500 mg/m²/dose) (arm A) or a continuous infusion (500 mg/m²/day) (arm B). Ara-CTP levels and inhibition of DNA synthesis increased from day 1 to day 2, but were not different between the two arms. In addition, the median blast percentages at day 15 did not differ between arms A and B, but patients treated in arm A had shorter intervals between the initiation of the first and second courses of therapy. Thus, although there were trends towards better CR rates and overall survival for patients treated in arm B, the reduced efficacy of arm A may have been partially compensated by more intense timing of therapy for that group. For all patients, 5-yr event-free survival and overall survival estimates were 44.1% ± 5.4 % and 50.0% ± 5.5%. Our results suggest that cladribine in combination with continuous-infusion cytarabine is effective therapy for childhood AML.

The clinical feature of invasive fungal infection in pediatric patients with hematologic and malignant diseases: a 10-year analysis at a single institution at Japan

Invasive fungal infections (IFI) are an important complication in hematologic malignancies and stem-cell transplantation (SCT). However, there are limited data characterizing IFI in children. The clinical feature of IFI after chemotherapy and SCT were analyzed in 334 pediatric patients treated at Hokkaido University Hospital from 1997 to 2006. The cumulative incidence of IFI was 6.9%; this comprised cases of proven, probable and possible IFI at rates of 1.2%, 3.0%, and 2.7%, respectively. The infected lesions were lung in 14 patients, liver in 5 patients, brain in 3 patients, fungemia in 2 patients, kidney in 1 patient, and endophthalmitis in 1 patient. The mortality of IFI was 48.2%, excluding patients who died due to relapse and interstitial pneumonitis; in particular, 71.4% patients with a lung lesion (10/14) died due to IFI. Fifty-nine pediatric patients died in our institution over the 10-year period of the study and IFI was the direct cause of death in 18.6% (11/59) of the patients. Risk factors for IFI with chemotherapy and SCT were also analyzed. Univariate analysis showed that age at diagnosis older than 10 years, relapse of original disease, long-term administration of broad-spectrum antibiotics, and acute myelogenous leukemia (AML) were the risk factors for IFI. All patients with IFI received long-term antibiotic therapy. AML was most strongly associated using a multivariate analysis. The prognosis of IFI has been expected poor; therefore, prevention of this condition, especially for older patients with AML, would be important.

Recent advances in management of acute myeloid leukemia (AML)

Acute myeloid leukemia (AML) is the most common childhood malignancy. AML has therapeutically been difficult to treat. In 2001, the World Health Organization (WHO), in conjunction with the Society for Hematopathology and the European Association of Hematopathology, published a new classification for myeloid neoplasms. A number of chromosomal abnormalities are used to predict outcome and stratify therapeutic risk groups in children with AML. Recently, alterations in receptor tyrosine kinases, tyrosine phosphatases and in oncogenes such as RAS have been implicated in the pathogenesis of AML. This article aims to review the recent development in diagnosis, treatment and monitoring of AML. Better understanding of the molecular pathogenesis of AML has led to the development of target-specific therapies. Some of the new classes of drugs include monoclonal antibody directed against the CD33 antigen, farnesyltransferase inhibitors (FTI), and FMSlike tyrosine kinase 3 (FLT3) inhibitors. The role of allogenic SCT, particularly whether it should be done during first CR or reserved for second remission, remains the most controversial issue in pediatric AML. There is a need of collaboration with international pediatric cooperative oncology groups and definitive clinical trials in order to establish use of these newer molecules in pediatric populations.

Acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias that result from clonal transformation of hematopoietic precursors through the acquisition of chromosomal rearrangements and multiple gene mutations. As a result of highly collaborative clinical research by pediatric cooperative cancer groups worldwide, disease-free survival has improved significantly during the past 3 decades. Further improvements in outcomes of children who have AML probably will reflect continued progress in understanding the biology of AML and the concomitant development of new molecularly targeted agents for use in combination with conventional chemotherapy drugs.

The development of a novel protocol for the treatment of de novo childhood acute myeloid leukemia in a single institution in Taiwan

From November 1, 1995 to July 31, 2004, 49 children with de novo acute myeloid leukemia (AML) were treated at our institution. One patient who was treated by a different protocol was excluded. In total, 48 patients with de novo AML were enrolled in this study. Forty-two patients with AML other than acute promyelocytic leukemia (non-APL) were treated consecutively with 2 novel protocols: Mackay Memorial Hospital (MMH)-AML-96, designed as a pilot phase, and Taiwan Pediatric Oncology Group (TPOG)-AML-97A, on the basis of MMH-AML-96 with minor modifications. Six patients with APL were treated consecutively with 2 protocols, TPOG-APL-97 and APL-2001. As of July 31, 2006, the remission rates were 79%, 92%, and 98% after 1, 2, and 3 courses of induction therapy, respectively. The 5-year overall survival was 64%+/-6.9% (SE), and the 5-year event-free survival was 60%+/-7.1%; for non-APL AML, the rates were 62%+/-7.5% and 59%+/-7.6%; for APL, 83+/-15.2 and 67+/-19.3%. Among the factors analyzed, a complete remission achieved after 1 course of induction therapy, lactate dehydrogenase <500 IU/L at diagnosis, patients without invasive fungal infection during chemotherapy, and male sex were associated with a favorable outcome.

Scholastic Achievements of Childhood Leukemia Patients: A Nationwide, Register-Based Study

Purpose

Studies concerning the scholastic achievement of survivors of childhood leukemia have yielded controversial results. We studied the school marks of childhood leukemia survivors in a register-based study.

Patients and Methods

Three hundred seventy-one patients with a diagnosis of leukemia before the age of 16 years who were born between 1974 and 1986 and alive on their 16th birthday were identified from the Finnish Cancer Registry. Five matched controls were sought for each patient from the Population Register Center of Finland. Information on the ninth-grade school report was obtained from Statistics Finland. The overall mark average and the marks (scale 4 to 10) for mother tongue, foreign language, mathematics, and physical education were compared between the patients and controls.

Results

The ninth-grade school report was obtained by 97.6% of the patients and 98.5% of the controls. The patients whose treatment included cranial irradiation had a lower overall mark average (mean difference, −0.24; 95% CI, −0.33 to −0.15) and lower marks for all assessed school subjects compared with their controls. Of the patients treated with chemotherapy alone, only the females with leukemia diagnosed before 7 years of age had lower school marks than their controls. The biggest difference was observed in the marks for foreign language among the irradiated females diagnosed at a young age (mean difference, −1.0; 95% CI, −1.25 to −0.74).

Conclusion

Leukemia treatment that includes cranial irradiation impairs scholastic achievement. It is noteworthy that treatment of leukemia with chemotherapy alone impairs school performance only in females diagnosed before school age.

Predictive value of multidrug resistance proteins and cellular drug resistance in childhood relapsed acute lymphoblastic leukemia

PURPOSE

Cellular resistance in childhood acute leukemias might be related to profile and function of multidrug resistance proteins and apoptosis regulating proteins. The aims of the study were: (1) analysis of expression of MRP1, PGP1, LRP, BCL-2 and p53 proteins; (2) correlation with ex vivo drug resistance, and (3) analysis of their prognostic impact on clinical outcome in childhood acute lymphoblastic (ALL) and acute myeloid (AML) leukemia.

METHODS

Total number of 787 children diagnosed for initial ALL (n = 527), relapsed ALL (n = 104), initial AML (n = 133) and relapsed AML (n = 23) were included into the study. Mean follow-up period was 3.5 years. Drug resistance for up to 30 anticancer agents was performed by the MTT assay. Expression of all proteins was tested by flow cytometry.

RESULTS

Both initial AML and relapsed ALL samples showed higher drug resistance than initial ALL samples. No significant differences were found in drug resistance between initial and relapsed AML samples. The presence of multidrug resistance and apoptosis proteins had no impact on pDFS in iALL and iAML, however strong trend towards adverse prognostic impact of MRP1, PGP and LRP on pDFS in rALL was observed. The same trend was observed for each of analyzed co-expressions of tested multidrug resistance proteins.

CONCLUSIONS

The phenomenon of cellular drug resistance in childhood acute leukemias is multifactorial and plays an important role in response to therapy. Expression of MRP1, PGP and LRP proteins, as well as their co-expression play possible role in childhood relapsed ALL.

Survival following relapse in childhood haematological malignancies diagnosed in 1974-2003 in Yorkshire, UK

We examined population-based information on relapsed childhood haematological cancers, investigating factors that might influence both overall survival and survival following relapse among the 1177 children (0-14 years) diagnosed with a haematological malignancy in Yorkshire from 1974 to 2003, of whom 342 (29%) relapsed at least once. Leukaemia patients from more deprived areas were significantly less likely to relapse (odds ratio=0.54, 95% confidence interval 0.32-0.93 for most deprived quintile vs least deprived quintile; P(trend)=0.06), especially those with acute myeloid leukaemia (P=0.04). Neither ethnic group nor distance to the main treatment centre was associated with risk of relapse. Overall, patients who relapsed at least once had 5-year survival rates of 46% (41-51%) compared with 79% (76-81%) of those who did not. Five-year survival rates from the time of first relapse increased from 20% in 1974-1983 to 45% in 1984-2003. Length of first remission was a strong predictor of survival for leukaemia with a 46% reduced risk of death for every additional year of event-free survival. Of children who experienced a relapse, 46% survived at least 5 years, whereas just under half of patients survived 5 years beyond disease recurrence. This provides a baseline for future comparisons and demonstrates that relapsed childhood cancer need not imply a poor outcome.

Improved outcome after relapse in children with acute myeloid leukaemia

In the Nordic Society for Paediatric Haematology and Oncology paediatric study acute myeloid leukaemia (AML) 93, event-free survival was 50% and overall survival was 66%, indicating that many patients were cured following relapse. Factors influencing outcome in children with relapsed AML were investigated. The study included all 146 children in the Nordic countries diagnosed with AML between 1988 and 2003, who relapsed. Data on disease characteristics and relapse treatment were related to outcome. Sixty-six percentage achieved remission with survival after relapse (5 years) 34 +/- 4%. Of 122 patients who received re-induction therapy, 77% entered remission with 40 +/- 5% survival. Remission rates were similar for different re-induction regimens but fludarabine, cytarabine, granulocyte colony-stimulating factor-based therapy had low treatment-related mortality. Prognostic factors for survival were duration of first complete remission (CR1) and stem cell transplantation (SCT) in CR1. In early relapse (<1 year in CR1), survival was 21 +/- 5% compared with 48 +/- 6% in late relapse. For children receiving re-induction therapy, survival in early relapse was 29 +/- 6% and 51 +/- 6% in late. Patients treated in CR1 with SCT, autologous SCT or chemotherapy had a survival of 18 +/- 9, 5 +/- 5 and 41 +/- 5%, respectively. Survival was 62 +/- 6% in 64 children given SCT as part of their relapse therapy. A significant proportion of children with relapsed AML can be cured, even those with early relapse. Children who receive re-induction therapy, enter remission and proceed to SCT can achieve a cure rate of 60%.

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.

Minimal residual disease directed therapy for childhood acute myeloid leukaemia: the time is now

The continued improvement in the prognosis of childhood acute myeloid leukaemia (AML) has been paralleled by the use of increasingly intensive therapy. This has led to attempts to develop risk-directed strategies in which the most intensive treatment is reserved for those at highest risk of relapse. Unfortunately, current approaches, which rely on cytogenetic sub-grouping and morphological assessment of response to therapy, are inaccurate. New prognostic factors are needed. This annotation proposes that the introduction of protocols based on the measurement of minimal residual disease (MRD) holds the key to progression from an era of 'cure at all costs' to a more individualised approach. However, the full potential of MRD technologies will only be realised through properly designed studies with scrupulous attention to logistics and quality assurance. The article illustrates which children may benefit most from MRD analysis in AML and explores practical issues that should be addressed in the design of clinical trials.

Proteasome inhibition as novel treatment strategy in leukaemia

Following its success in multiple myeloma (MM), proteasome inhibition has become a topic of interest as novel treatment strategy of cancer. By simultaneously affecting multiple pathways in the cancer cell, such as deregulation of the programmed degradation of many cellular proteins, proteasome inhibition causes rapid apoptosis of these cells. Both in rapidly proliferating leukaemic cell lines and in primary leukaemic cells isolated from patients, proteasome inhibition results in antileukaemic activity. The normal counterparts of these cells are much more resistant to proteasome inhibitors (PI), thereby resulting in a favourable therapeutic index. Importantly, while leukaemic stem cells are sensitive to proteasome inhibition, normal haematopoietic stem cells are still viable after drug exposure. Nowadays, many PIs are being identified; bortezomib is the most well known since obtaining Food and Drug Administration approval for clinical use in MM. This review summarises the biological and clinical aspects of proteasome inhibition and discusses the potential role of these inhibitors in the treatment of leukaemia.

Treatment strategy and long-term results in paediatric patients treated in consecutive UK AML trials

Between 1988 and 2002, 758 children with acute myeloid leukaemia (AML) were treated on Medical Research Council (MRC) AML 10 and AML 12. MRC AML 10 tested the role of bone marrow transplantation following four blocks of intensive chemotherapy and found that while both allogeneic bone marrow transplant (allo-BMT) and autologous bone marrow transplant (A-BMT) significantly reduced the relapse risk (RR), this did not translate into a significant improvement in overall survival (OS). A risk group stratification based on cytogenetics and response to the first course of chemotherapy derived from MRC AML 10 was used to deliver risk-directed therapy in MRC AML 12. Allo-BMT was limited to standard and poor risk patients and A-BMT was not employed. Instead, the benefit of an additional block of treatment was tested by randomising children to receive either four or five blocks of treatment in total. While the results of MRC AML 12 remain immature, there appears to be no survival advantage for a fifth course of treatment. The 5 year OS, disease-free survival (DFS), event-free survival (EFS) and RR in MRC AML 12 are 66, 61, 56 and 35%, respectively; at present superior to MRC AML 10, which had a 5-year OS, DFS, EFS and RR of 58, 53, 49 and 42%, respectively. MRC AML trials employ a short course of triple intrathecal chemotherapy alone for CNS-directed treatment and CNS relapse is uncommon. Improvements in supportive care have contributed to improved outcomes and the number of deaths in remission fell between trials. Anthracycline-related cardiotoxicity remains a concern and the current MRC AML 15 trial tests the feasibility of reducing anthracycline dosage without compromising outcome by comparing standard MRC anthracycline-based consolidation with high-dose ara-C. MRC studies suggest that the role of allo-BMT is limited in 1st CR and that there may be a ceiling of benefit from current or conventional chemotherapy.

Results of 58872 and 58921 trials in acute myeloblastic leukemia and relative value of chemotherapy vs allogeneic bone marrow transplantation in first complete remission: the EORTC Children Leukemia Group report

The first EORTC (European Organization of Research and Treatment of Cancer) acute myeloblastic leukemia (AML) pilot study (58872) was conducted between January 1988 and December 1991. Out of 108 patients, 78% achieved complete remission (CR), and event-free survival (EFS) and survival rates (s.e., %) at 7 years were 40 (5) and 51% (6%), respectively. It indicated that mitoxantrone could be substituted for conventional anthracyclines in the treatment of childhood AML without inducing cardiotoxicity. The aim of the next EORTC 58921 trial was to compare the efficacy and toxicity of idarubicin vs mitoxantrone in initial chemotherapy courses, further therapy consisting of allogeneic bone marrow transplantation (alloBMT) in patients with an HLA-compatible sibling donor or chemotherapy in patients without a donor. Out of 177 patients, recruited between October 1992 and December 2002, 81% reached CR. Overall 7-year EFS and survival rates were 49 (4) and 62% (4%), respectively. Out of 145 patients who received the first intensification, 39 had a sibling donor. In patients with or without a donor, the 7-year disease-free survival (DFS) rate was 63 (8) and 57% (5%) and the 7-year survival rate was 78 (7) and 65% (5%), respectively. Patients with favorable, intermediate and unfavorable cytogenetic features had a 5-year EFS rate of 57, 45 and 45% and a 5-year survival rate of 89, 67 and 53%, respectively.