This review reports about the main steps of development in pediatric acute myeloid leukemia (AML) concerning diagnostics, treatment, risk groups, and outcomes. Finally, a short overview of present and future approaches is given.

Approximately 10% of children with cancer harbor a mutation in a predisposition gene. In children with the kidney cancer Wilms tumor, the prevalence is as high as 30%. Certain predispositions are associated with defined histological and clinical features, suggesting differences in tumorigenesis. To investigate this, we assembled a cohort of 137 children with Wilms tumor, of whom 71 had a pathogenic germline or mosaic variant. We examined 237 neoplasms (including two secondary leukemias), utilizing whole-genome sequencing, RNA sequencing, and genome-wide methylation, validating our findings in an independent cohort. Tumor development differed in children harboring a predisposition, depending on the variant gene and its developmental timing. Differences pervaded the repertoire of driver events, including high-risk mutations, the clonal architecture of normal kidneys, and the relatedness of neoplasms from the same individual. Our findings indicate that predisposition may preordain Wilms tumorigenesis, suggesting a variant-specific approach to managing children merits consideration. Significance: Tumors that arise in children with a cancer predisposition may develop through the same mutational pathways as sporadic tumors. We examined this question in the childhood kidney cancer, Wilms tumor. We found that certain predispositions dictate the genetic development of tumors, with clinical implications for these children. See related commentary by Brzezinski and Malkin, p. 258

Detection of somatic mutations in single cells has been severely hampered by technical limitations of whole genome amplification. Novel technologies including primary template-directed amplification (PTA) significantly improved the accuracy of single-cell whole genome sequencing (WGS), but still generate hundreds of artefacts per amplification reaction. We developed a comprehensive bioinformatic workflow, called the PTA Analysis Toolkit (PTATO), to accurately detect single base substitutions, small insertions and deletions (indels) and structural variants in PTA-based WGS data. PTATO includes a machine learning approach to distinguish PTA-artefacts from true mutations with high sensitivity (up to 90% for base substitution and 95% for indels), outperforming existing bioinformatic approaches. Using PTATO, we demonstrate that many hematopoietic stem and progenitor cells of patients with Fanconi anemia, which cannot be analyzed using regular WGS technologies, have normal somatic single base substitution burdens, but increased numbers of deletions. Our results show that PTATO enables studying somatic mutagenesis in the genomes of single cells with unprecedented sensitivity and accuracy.

Therapy-related acute myeloid leukemia (AML; tAML) is one of the most feared therapy-emergent complications. This study aims to determine the clinical and pathological significance and define therapeutic implications and poor prognosticators in pediatric tAML. We analyzed a total of 119 pediatric patients (aged 2-20 years) who were centrally diagnosed with tAML within the Acute Myeloid Leukemia Berlin-Frankfurt-Münster (AML-BFM) study group between 1993 and 2019. Compared with de novo AML, tAML was associated with decreased white blood count and involvement of the central nervous system. Latency to tAML was inversely correlated with age at primary malignancy. Patients with tAML were more likely to have abnormal karyotypes, overrepresenting KMT2A rearrangements, the unfavorable cytogenetics –7/del(7q), as well as complex and monosomal karyotypes, whereas core-binding AML was underrepresented. The occurrence of stratification-relevant molecular genetics was comparable with de novo AML, whereas CEBPAdm was absent in tAML. Survival rates in tAML improved from 10% ± 6% in AML-BFM 1993/1998 to 50% ± 10% in the registries 2012/2017; however, this is still worse than de novo AML. Hematopoietic stem cell transplantation (HSCT) in no evidence of leukemia (NEL; 35 Gy), and latency ≤1 year were identified as the strongest poor prognosticators. Over the past 26 years, outcome and survival significantly improved in pediatric tAML. Our results suggest that HSCT in NEL after 2 induction cycles is the most promising therapeutic approach for achieving improved survival. Radiation, adverse cytogenetics, and latency ≤1 year should be considered as poor prognosticators in pediatric tAML.

In AML, the assessment of response is one of the most important prognostic markers and is crucial for assessing clinical trials. Remission criteria for AML defined by Cheson et al. has remained virtually unchanged over the last two decades. Here we revised response criteria and provide a more precise standard for evaluating treatment outcomes in paediatric AML. A multicentre analysis of real-time data of 1094 paediatric patients diagnosed between 2004 and 2021 within the AML-BFM study group was conducted, categorising them into two alternative response groups “evidence of leukaemia” (EL, ≥5% blasts) and “no evidence of leukaemia” (NEL, <5% blasts) and comparing those with the previous CR versus no-CR classification across three different treatment timepoints. The survival of patients newly classified as NEL was comparable to that of patients with CR. The revised NEL/EL comparison showed better predictive power in terms of survival than the former CR/no-CR classification. The poorest outcome at the end of induction (EOI) was noticed in patients with EL, which could be improved by HSCT. Stratification by NEL/EL revealed the highest independent predictive effect on overall and event-free survival. The integration of measurable residual disease monitoring using reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) further improved the predictive power of the revised definition. By simplifying the response criteria for morphological assessment of blast persistence (NEL/EL), we provide an improved and more precise definition of response for paediatric AML, which presents a new milestone with a high prognostic impact in daily clinical practice and in interpreting clinical trials. 10.13039/501100005972 Deutsche Krebshilfe e.V. , 10.13039/501100008349 University of Duisburg-Essen .

Contains Supplementary Tables 1-8. Supplementary Table 1 shows characteristics of discovery cohort. Supplementary Table 2 shows genes included in predisposition analysis. Supplementary Table 3 shows evidence underlying novel predispositions. Supplementary Table 4 shows variants that would be detectable by current clinical assays. Supplementary Table 5 shows substitutions and indels. Supplementary Table 6 shows rearrangements. Supplementary Table 7 shows 10,000 most variable probes. Supplementary Table 8 shows differentially expressed genes.