Jessica A. Pollard

Prevalence and prognostic implications of CEBPA mutations in pediatric acute myeloid leukemia (AML): a report from the Children's Oncology Group

CEBPA mutations have been associated with improved outcome in adult acute myeloid leukemia (AML). We evaluated the prevalence and prognostic significance of CEBPA mutations in 847 children with AML treated on 3 consecutive pediatric trials. Two types of CEBPA mutations-N-terminal truncating mutations and in-frame bZip-domain mutations-were detected in 38 (4.5%) of 847 patients tested; 31 (82%) of 38 patients with mutations harbored both mutation types. Mutation status was correlated with laboratory and clinical characteristics and clinical outcome. CEBPA mutations were significantly more common in older patients, patients with FAB M1 or M2, and patients with normal karyotype. Mutations did not occur in patients with either favorable or unfavorable cytogenetics. Actuarial event-free survival at 5 years was 70% versus 38% (P = .015) with a cumulative incidence of relapse from complete remission of 13% versus 44% (P = .007) for those with and without CEBPA mutations. The presence of CEBPA mutations was an independent prognostic factor for improved outcome (HR = 0.24, P = .047). As CEBPA mutations are associated with lower relapse rate and improved survival, CEBPA mutation analysis needs to be incorporated into initial screening for risk identification and therapy allocation at diagnosis.

Prevalence and prognostic significance of KIT mutations in pediatric patients with core binding factor AML enrolled on serial pediatric cooperative trials for de novo AML.

KIT receptor tyrosine kinase mutations are implicated as a prognostic factor in adults with core binding factor (CBF) acute myeloid leukemia (AML). However, their prevalence and prognostic significance in pediatric CBF AML is not well established. We performed KIT mutational analysis (exon 8 and exon 17) on diagnostic specimens from 203 pediatric patients with CBF AML enrolled on 4 pediatric AML protocols. KIT mutations were detected in 38 (19%) of 203 (95% CI, 14%-25%) patient samples of which 20 (52.5%) of 38 (95% CI, 36%-69%) involved exon 8, 17 (45%) of 38 (95% CI, 29%-62%) involved exon 17, and 1 (2.5%; 95% CI, 0%-14%) involved both locations. Patients with KIT mutations had a 5-year event-free survival of 55% (+/- 17%) compared with 59% (+/- 9%) for patients with wild-type KIT (P = .86). Rates of complete remission, overall survival, disease-free survival, or relapse were not significantly different for patients with or without KIT mutations. Location of the KIT mutation and analysis by cytogenetic subtype [t(8;21) vs inv(16)] also lacked prognostic significance. Our study shows that KIT mutations lack prognostic significance in a large series of pediatric patients with CBF AML. This finding, which differs from adult series and a previously published pediatric study, may reflect variations in therapeutic approaches and/or biologic heterogeneity within CBF AML. Two of 4 studies included in this analysis are registered at http://clinicaltrials.gov as NCT00002798 (CCG-2961) and NCT00070174 (COG AAML03P1).

Prevalence and prognostic implications of CEBPA mutations in pediatric AML: a report from the Children's Oncology Group

CEBPA mutations have been associated with improved outcome in adult acute myeloid leukemia (AML). We evaluated the prevalence and prognostic significance of CEBPA mutations in 847 children with AML treated on 3 consecutive pediatric trials. Two types of CEBPA mutations-N-terminal truncating mutations and in-frame bZip-domain mutations-were detected in 38 (4.5%) of 847 patients tested; 31 (82%) of 38 patients with mutations harbored both mutation types. Mutation status was correlated with laboratory and clinical characteristics and clinical outcome. CEBPA mutations were significantly more common in older patients, patients with FAB M1 or M2, and patients with normal karyotype. Mutations did not occur in patients with either favorable or unfavorable cytogenetics. Actuarial event-free survival at 5 years was 70% versus 38% (P = .015) with a cumulative incidence of relapse from complete remission of 13% versus 44% (P = .007) for those with and without CEBPA mutations. The presence of CEBPA mutations was an independent prognostic factor for improved outcome (HR = 0.24, P = .047). As CEBPA mutations are associated with lower relapse rate and improved survival, CEBPA mutation analysis needs to be incorporated into initial screening for risk identification and therapy allocation at diagnosis.

The role of competition in word learning via referent selection

Previous research suggests that competition among the objects present during referent selection influences young childrens ability to learn words in fast mapping tasks. The present study systematically explored this issue with 30-month-old children. Children first received referent selection trials with a target object and either two, three or four competitor objects. Then, after a short delay, children were tested on their ability to retain the newly fast-mapped names. Overall, the number of competitors did not affect childrens ability to form the initial name-object mappings. However, only children who encountered few competitors during referent selection demonstrated significant levels of retention. Results and implications are discussed in terms of the role of competition in studies of childrens fast mapping. The relationship between referent selection and full word learning is also discussed.

Correlation of CD33 expression level with disease characteristics and response to gemtuzumab ozogamicin containing chemotherapy in childhood AML

CD33 is expressed on the majority of acute myeloid leukemia (AML) leukemic blasts and is the target for gemtuzumab ozogamicin (GO), a toxin-conjugated anti-CD33 mAb. In the present study, we quantified the CD33 mean fluorescent intensity of leukemic blasts prospectively in 619 de novo pediatric AML patients enrolled in Childrens Oncology Group GO-containing clinical trials and determined its correlation with disease characteristics and clinical outcome. CD33 expression varied more than 2-log fold; a median mean fluorescent intensity of 129 (range, 3-1550.07) was observed. Patients were divided into 4 quartiles, quartiles 1-4 (Q1-4) based on expression and disease characteristics and clinical response defined across quartiles. High CD33 expression was associated with high-risk FLT3/ITD mutations (P < .001) and was inversely associated with low-risk disease (P < .001). Complete remission (CR) rates were similar, but patients in Q4 had significantly lower overall survival (57% ± 16% vs 77% ± 7%, P = .002) and disease-free survival from CR (44% ± 16% vs 62% ± 8%, P = .022). In a multivariate model, high CD33 expression remained a significant predictor of overall survival (P = .011) and disease-free survival (P = .038) from CR. Our findings suggest that CD33 expression is heterogeneous within de novo pediatric AML. High expression is associated with adverse disease features and is an independent predictor of inferior outcome. The correlation between CD33 expression and GO response is under investigation. These studies are registered at www.clinicaltrials.gov as NCT00070174 and NCT00372593.

Results of a Prospective Multicenter Phase II Study of Initial Treatment with Methotrexate In LGL Leukemia (ECOG Protocol E5998)

Recent studies of WT1 mutations in acute myeloid leukemia (AML) mostly report an association with unfavorable clinical outcome. We screened 842 patients treated on 3 consecutive pediatric AML trials for WT1 zinc-finger mutations. Eighty-five mutations were detected in 70 of 842 patients (8.3%). Mutations occurred predominantly in exon 7 (n = 74) but were also found in exons 8 (n = 5) and 9 (n = 6). Normal karyotype was observed in 35.3% of WT1(mut) patients, whereas 27.5% WT1(mut) patients harbored favorable risk cytogenetics. Patients with or without mutations had similar rates of complete remission after one course of induction chemotherapy. Overall survival (OS) for patients with WT1 mutations was 41% versus 54% for those without mutations (P = .016). Corresponding event-free survival (EFS) was also significantly worse for those with WT1 mutations (28% vs 42%; P = .01). However, FLT3/ITD was present in 36% of the WT1(mut) cohort; WT1(mut) patients without FLT3/ITD had similar OS (56% vs 56%, respectively; P = .8) and EFS (35% and 44%, respectively; P = .34) to patients who were wild type for both mutations. In current risk stratification schemes incorporating cytogenetics and FLT3/ITD status, the presence of WT1 mutations has no independent prognostic significance in predicting outcome in pediatric AML. The clinical trials are registered at www.clinicaltrials.gov as #NCT00002798 and #NCT00070174.

CD33 Expression and Its Association With Gemtuzumab Ozogamicin Response: Results From the Randomized Phase III Children's Oncology Group Trial AAML0531.

PURPOSE CD33 is variably expressed on acute myeloid leukemia (AML) blasts and is targeted by gemtuzumab ozogamicin (GO). GO has shown benefit in both adult and pediatric AML trials, yet limited data exist about whether GO response correlates with CD33 expression level. PATIENTS AND METHODS CD33 expression levels were prospectively quantified by multidimensional flow cytometry in 825 patients enrolled in Childrens Oncology Group AAML0531 and correlated with response to GO. RESULTS Patients with low CD33 expression (lowest quartile of expression [Q1]) had no benefit with the addition of GO to conventional chemotherapy (relapse risk [RR]: GO 36% v No-GO 34%, P = .731; event-free survival [EFS]: GO 53% v No-GO 58%, P = .456). However, patients with higher CD33 expression (Q2 to Q4) had significantly reduced RR (GO 32% v No-GO 49%, P < .001) and improved EFS (GO 53% v No-GO 41%, P = .005). This differential effect was observed in all risk groups. Specifically, low-risk (LR), intermediate-risk (IR), and high-risk (HR) patients with low CD33 expression had similar outcomes regardless of GO exposure, whereas the addition of GO to conventional chemotherapy resulted in a significant decrease in RR and disease-free survival (DFS) for patients with higher CD33 expression (LR RR, GO 13% v No-GO 35%, P = .001; LR DFS, GO 79% v No-GO 59%, P = .007; IR RR, GO 44% v No-GO 57%, P = .044; IR DFS, GO 51% v No-GO 40%, P = .078; HR RR, GO 40% v No-GO 73%, P = .016; HR DFS, GO 47% v No-GO 28%, P = .135). CONCLUSION We demonstrate that GO lacks clinical benefit in patients with low CD33 expression but significantly reduces RR and improves EFS in patients with high CD33 expression, which suggests a role for CD33-targeted therapeutics in subsets of pediatric AML.

Sorafenib treatment following hematopoietic stem cell transplant in pediatric FLT3/ITD acute myeloid leukemia

FLT3/ITD is associated with poor outcomes in adult and pediatric acute myeloid leukemia (AML). Allogeneic hematopoietic stem cell transplantation (HSCT) can improve cure rates, however relapse is still common. Recent studies demonstrate the activity of FLT3 inhibitors, including sorafenib, in targeting the underlying mutation.

Clinical Significance of CD33 Nonsynonymous Single-Nucleotide Polymorphisms in Pediatric Patients with Acute Myeloid Leukemia Treated with Gemtuzumab-Ozogamicin–Containing Chemotherapy

Purpose: The purpose of this study was to evaluate clinical implications of CD33 single-nucleotide polymorphisms (SNP) in pediatric patients with acute myeloid leukemia (AML) treated with gemtuzumab-ozogamicin (GO)–based therapy. Experimental Design: We genotyped four CD33 SNPs: rs35112940 (G>A; Arg304Gly), rs12459419 (C>T; Ala14Val), rs2455069 (A>G; Arg69Gly), and rs1803254 (G>C; 3′UTR) in pediatric patients undergoing induction chemotherapy containing GO (COG-AAML03P1 trial; n = 242) or not containing GO (St. Jude AML02 trial; n = 172). Results: CD33 SNPs were correlated significantly with clinical characteristics and treatment outcome. The coding SNPs, rs35112940 and rs12459419, were significantly associated with clinical endpoints in COG-AAML03P1 but not in the St. Jude AML02 trial. Specifically, among white patients in COG-AAML03P1, the 3-year overall survival (OS) rate from remission was 84% ± 8% for those homozygous (GG) for rs35112940 versus 68% ± 15% for the other genotypes (P = 0.018); these patients also had a lower relapse risk and superior disease-free survival. Likewise, patients homozygous for variant allele (TT) for rs12459419 were more likely to have favorable risk disease than CC and CT genotypes (52% vs. 31%, P = 0.034) and significantly lower diagnostic blast CD33 expression than other genotypes (P < 0.001). Conclusion: Our data suggest that genetic variations in CD33 could impact clinical outcome of GO-based therapy in pediatric AMLs. Clin Cancer Res; 19(6); 1620–7. ©2013 AACR.

CD33 Splicing Polymorphism Determines Gemtuzumab Ozogamicin Response in De Novo Acute Myeloid Leukemia: Report From Randomized Phase III Children’s Oncology Group Trial AAML0531

Purpose Gemtuzumab ozogamicin (GO), a CD33-targeted immunoconjugate, is a re-emerging therapy for acute myeloid leukemia (AML). CD33 single nucleotide polymorphism rs12459419 C>T in the splice enhancer region regulates the expression of an alternatively spliced CD33 isoform lacking exon2 (D2-CD33), thus eliminating the CD33 IgV domain, which is the antibody-binding site for GO, as well as diagnostic immunophenotypic panels. We aimed to determine the impact of the genotype of this splicing polymorphism in patients with AML treated with GO-containing chemotherapy. Patients and Methods CD33 splicing single nucleotide polymorphism was evaluated in newly diagnosed patients with AML randomly assigned to receive standard five-course chemotherapy alone (No-GO arm, n = 408) or chemotherapy with the addition of two doses of GO once during induction and once during intensification (GO arm, n = 408) as per the Childrens Oncology Group AAML0531 trial. Results The rs12459419 genotype was CC in 415 patients (51%), CT in 316 patients (39%), and TT in 85 patients (10%), with a minor allele frequency of 30%. The T allele was significantly associated with higher levels of D2-CD33 transcript ( P < 1.0E-6) and with lower diagnostic leukemic cell surface CD33 intensity ( P < 1.0E-6). Patients with the CC genotype had significantly lower relapse risk in the GO arm than in the No-GO arm (26% v 49%; P < .001). However, in patients with the CT or TT genotype, exposure to GO did not influence relapse risk (39% v 40%; P = .85). Disease-free survival was higher in patients with the CC genotype in the GO arm than in the No-GO arm (65% v 46%, respectively; P = .004), but this benefit of GO addition was not seen in patients with the CT or TT genotype. Conclusion Our results suggest that patients with the CC genotype for rs12459419 have a substantial response to GO, making this a potential biomarker for the selection of patients with a likelihood of significant response to GO.