Infection, immune responses and the aetiology of childhood leukaemia

New hPSC-based human models to study pediatric Acute Megakaryoblastic Leukemia harboring the fusion oncogene RBM15-MKL1

Pediatric Acute Megakaryoblastic Leukemia not associated to Down Syndrome (non-DS AMKL) is a rare disease with a dismal prognosis. Around 15% of patients carry the chromosomal translocation t(1;22) that originates the fusion oncogene RBM15-MKL1, which is linked to an earlier disease onset (median of 6months of age) and arises in utero. Here we report the generation of two hPSC cell lines constitutively expressing the oncogene RBM15-MKL1, resulting in an increased expression of known RBM15-MKL1 gene targets. These cell lines represent new disease models of pediatric AMKL to study the impact of the RBM15-MKL1 oncogene on human embryonic hematopoietic development.

Risk of Childhood Cancer and Socio-economic Disparities: Results of the French Nationwide Study Geocap 2002-2010

BACKGROUND

Socio-economic status is related to many life style and environmental factors, some of which have been suggested to influence the risk of childhood cancer. Studies requiring subject participation are usually hampered by selection of more educated parents. To prevent such bias, we used unselected nationwide Geographical Information System (GIS)-based registry data, to investigate the influence of socio-economic disparities on the risk of childhood cancer.

METHODS

The Geocap study included all French residents diagnosed with cancer aged up to 15 years over the period 2002-2010 (15 111 cases) and 45 000 contemporaneous controls representative of the childhood population. Area socio-economic characteristics used to calculate the European Deprivation Index (EDI) were based on census data collected on the fine scale of the Merged Islet for Statistical Information (IRIS).

RESULTS

Overall, the risk of acute lymphoblastic leukaemia (ALL) was lower in the most deprived quintile than in the other quintiles of EDI (OR_Q5vs<Q5 0.80 (95% confidence interval (CI) 0.73, 0.88)). The odds ratio for all the other cancers taken together was close to the null (OR_Q5vs<Q5 0.99 (95% CI 0.94, 1.04)).

CONCLUSION

Living in the most deprived areas was inversely associated with the risk of ALL in childhood. There was no indication that the risk of childhood cancer of any site could be increased by deprivation. Life style or environmental factors potentially underlying the association need further investigation.

Environmental Exposure and Risk of Childhood Leukemia: An Overview

Childhood leukemia is the most common cancer diagnosed in children worldwide. However, only a few causes have been established so far, mainly some genetic syndromes and high doses of ionizing radiation. Major efforts have been undertaken to study the relationship between environmental factors and the risk of childhood leukemia, inspired by geographical variation in incidence rates. Some evidence has emerged for parental occupational exposures to pesticides, whereas there is less evidence for an association with postnatal pesticide exposure. Diagnostic radiation and radon exposure have been suggested but there remains a lack of convincing studies. Extremely low-frequency magnetic fields consistently showed a small increase in risk in numerous studies, but bias and confounding cannot be ruled out as possible explanations. From among factors other than environmental and radiation-related, the most promising candidate is abnormal patterns to common infections, but which children are most at risk and the pathways are not fully understood. In conclusion, although childhood leukemia shows some distinct incidence patterns by sex, age, and geography suggesting a role of the environment in its etiology, no major environmental risk factors including radiation have been established as major contributors to the global childhood leukemia burden. Due to the young age at diagnosis and evidence of chromosomal damage before birth in many of the affected children, parental exposures remain of high interest. Although cure rates of childhood leukemia are high in economically developed countries, because of the adverse late effects of the disease and its treatment, identification of modifiable risk factors for implementing primary prevention remains the ultimate goal.

Pediatric T-cell acute lymphoblastic leukemia

The most common pediatric malignancy is acute lymphoblastic leukemia (ALL), of which T-cell ALL (T-ALL) comprises 10-15% of cases. T-ALL arises in the thymus from an immature thymocyte as a consequence of a stepwise accumulation of genetic and epigenetic aberrations. Crucial biological processes, such as differentiation, self-renewal capacity, proliferation, and apoptosis, are targeted and deranged by several types of neoplasia-associated genetic alteration, for example, translocations, deletions, and mutations of genes that code for proteins involved in signaling transduction, epigenetic regulation, and transcription. Epigenetically, T-ALL is characterized by gene expression changes caused by hypermethylation of tumor suppressor genes, histone modifications, and miRNA and lncRNA abnormalities. Although some genetic and gene expression patterns have been associated with certain clinical features, such as immunophenotypic subtype and outcome, none has of yet generally been implemented in clinical routine for treatment decisions. The recent advent of massive parallel sequencing technologies has dramatically increased our knowledge of the genetic blueprint of T-ALL, revealing numerous fusion genes as well as novel gene mutations. The challenges now are to integrate all genetic and epigenetic data into a coherent understanding of the pathogenesis of T-ALL and to translate the wealth of information gained in the last few years into clinical use in the form of improved risk stratification and targeted therapies. Here, we provide an overview of pediatric T-ALL with an emphasis on the acquired genetic alterations that result in this disease. © 2016 Wiley Periodicals, Inc.

Virome characterisation from Guthrie cards in children who later developed acute lymphoblastic leukaemia

Background:

Some childhood acute lymphoblastic leukaemias (ALL) can be traced back to a prenatal origin, where a virus infection could be involved in the first pre-leukaemic clone development. The DNA virome of 95 children who later developed ALL was characterised from neonatal blood spots (NBS) using unbiased next-generation sequencing (NGS) and compared with the virome of 95 non-ALL controls.

Methods:

DNA was individually extracted from the ALL-patients and controls, pooled, randomly amplified and sequenced using the Illumina MiSeq Sequencing System.

Results:

Virus-like sequences identified in both groups mapped to human endogenous retroviruses and propionibacterium phage, considered a part of the normal microbial flora. Potential pathogens human herpesvirus type 6 (HHV-6) and parvovirus B19 were also identified, but only few samples in both ALL and controls tested positive by PCR follow-up.

Conclusions:

Unbiased NGS was employed to search for DNA from potential infectious agents in neonatal samples of children who later developed ALL. Although several viral candidates were identified in the NBS samples, further investigation by PCR suggested that these viruses did not have a major role in ALL development.

Specific and Non-specific Clinical Presentations in the Year Before the Diagnosis of Childhood Leukaemia

INTRODUCTION

Clinical presentations of childhood leukaemia have been reported in case-only studies. The timing when these presentations start to occur prior to diagnosis is less clear.

METHODS

In this nested case-control study, 1,025 and 334 children with lymphoid and myeloid leukaemia, respectively, were matched (1:30) to population-based controls by sex, region and year of birth. An index date was assigned for each control when the matched case was diagnosed. Healthcare access records of cases and controls in the year before the index date were extracted.

RESULTS

Children with lymphoid leukaemia started to visit doctors more often at least 2 months before leukaemia diagnosis (P < 0.05). Various presentations were recorded in these visits: rates of haematological presentations, musculoskeletal presentations, and injuries started to increase significantly at least 3 months before diagnosis; rates of respiratory, gastrointestinal and urinary tract presentations did not increase significantly until the last month. The findings for myeloid lymphoma were less clear, but children appeared to visit doctors more often at least 4 months before diagnosis, and the rate of haematological presentations also started to increase at least 4 months before leukaemia diagnosis. Although haematological presentations were most strongly associated with undiagnosed leukaemia (odds ratio > 290 in the last month), the majority (>96%) of children with haematological presentations did not have leukaemia if they had not been diagnosed in their first visit.

CONCLUSIONS

We described a clinical picture in the year before leukaemia diagnosis. These findings revealed ongoing difficulties in early diagnosis of childhood leukaemia in healthcare settings.

Effects of Maternal Diet During Pregnancy on the Risk of Childhood Acute Lymphoblastic Leukemia: A Systematic Review

Acute lymphoblastic leukemia (ALL) is the most common type of leukemia in children that can be affected by maternal diet. The aim of this study was to evaluate maternal dietary risk factors of ALL. We searched MEDLINE, Cochrane Library, Springer Link, Wiley Online, Science Direct, Mosby, ISI Web of Science, OVID, ProQuest, and Scopus from database inception until February 2, 2016. Two reviewers scanned titles, abstracts, and keywords of articles after excluding duplicates. We included case-control studies evaluating the relationship between maternal diet during pregnancy and childhood ALL. The search resulted in 2,940 papers, of which 11 full-text articles met the criteria for inclusion in the review and were analyzed. The finding of these studies suggest that maternal diet composed largely of vegetables, fruits, and protein sources before and during pregnancy can reduce the risk of ALL in offspring. Maternal alcohol intake had no effect. Nevertheless, inherent limitations of case-control studies like measurement error, random error, recall bias, and selection bias preclude conclusive evidence. Persuading pregnant women to follow a healthy diet rich in fruits, vegetables, and protein may reduce the risk of childhood ALL. Avoiding alcohol intake seems prudent.

Regulation of the miRNA expression by TEL/AML1, BCR/ABL, MLL/AF4 and TCF3/PBX1 oncoproteins in acute lymphoblastic leukemia (Review)

MicroRNAs (miRNAs) are a class of small endogenous non-coding RNAs that play important regulatory roles by targeting mRNAs for cleavage or translational repression. miRNAs act in diverse biological processes including development, cell growth, apoptosis, and hematopoiesis. The miRNA expression is associated with specific cytogenetic changes and can also be used to discriminate between the different subtypes of leukemia in acute lymphoblastic leukemia with common translocations, it is shown that the miRNAs have the potential to be used for clinical diagnosis and prognosis. We reviewed the roles of miRNA here with emphasis on their function in human leukemia and the mechanisms of the TEL/AML1, BCR/ABL, MLL/AF4 and TCF3/PBX1 oncoproteins on miRNAs expression in acute lymphoblastic leukemia.

Association of atopic diseases and parvovirus B19 with acute lymphoblastic leukemia in childhood and adolescence in the northeast of Brazil

BACKGROUND

Several factors related to the immune system, such as a history of allergies and virus infections, may be associated with acute lymphoblastic leukemia (ALL). The purpose of this study was to analyze whether the presence of atopic diseases and previous infection with parvovirus B19 and Epstein-Barr virus (EBV) are associated with the development of ALL.

METHODS

This case-control study was performed in two tertiary hospitals located in northeastern Brazil. The study population included 60 patients who were diagnosed with non-T-cell ALL using myelogram and immunophenotyping and 120 patients in the control group. Atopy was evaluated via a parent questionnaire and medical records. Total immunoglobulin (Ig)E and IgG levels of parvovirus B19 and EBV were measured in the serum. Logistic regression was performed to assess the association between variables and odds of ALL.

RESULTS

We identified a significant inverse association between rhinitis, urticaria and elevated IgE serum levels with ALL. A history of parvovirus B19 infection showed a significant association with this type of cancer [OR (95 % CI) 2.00 (1.94-4.26); P = 0.050]. In logistic regression, the presence of atopy was a protective factor [OR (95 % CI) 0.57 (0.38-0.83); P = 0.004], and the presence of IgG for parvovirus B19 was an important risk factor for ALL [OR (95 % CI) 2.20 (1.02-4.76); P = 0.043].

CONCLUSIONS

These results suggest that atopic diseases and elevated total IgE levels are associated with a potential protective effect on the development of ALL. Previous infection with parvovirus B19 contributed to ALL susceptibility.

The Frequency of HLA-A, HLA-B, and HLA-DRB1 Alleles in Patients with Acute Lymphoblastic Leukemia in the Turkish Population: A Case-Control Study

We studied the frequencies of human leukocyte antigen alleles (A, B, and DRB1) in 90 patients with acute lymphoblastic leukemia (ALL) and then compared them with 126 controls in this study. Although the frequencies of the A*03 allele, the DRB1*03 allele, the DRB1*04 allele, the A*02/B*35/DRB1*13 haplotype, and homozygosity of A*02 were higher in patients (p=0.006, p=0.003, p=0.002, p=0.01, and p=0.02, respectively), the frequencies of the A*23, B*13, B*40, and DRB1*13 alleles were lower (p=0.002, p=0.07, p=0.002, and p=0.003, respectively) in patients than controls. The frequencies of the DRB1*04 and DRB1*07 alleles were higher in patients in the high-risk group and standard-risk group, respectively (p=0.009 and p=0.007, respectively). This study indicated that the frequency of the A*03 allele, the DRB1*03 allele, the DRB1*04 allele, the A*02/B*35/DRB1*13 haplotype, and A*02 homozygosity may play a predisposing role in patients with ALL in the Turkish population. The frequency of the DRB1*04 and DRB1*07 alleles may also be associated with high risk and standard risk in patients with ALL, respectively.

DNA methylation as a potential mediator of environmental risks in the development of childhood acute lymphoblastic leukemia

5-year survival rate for childhood acute lymphoblastic leukemia (ALL) has risen to approximately 90%, yet the causal disease pathway is still poorly understood. Evidence suggests multiple 'hits' are required for disease progression; an initial genetic abnormality followed by additional secondary 'hits'. It is plausible that environmental influences may trigger these secondary hits, and with the peak incidence of diagnosis between 2 and 5 years of age, early life exposures are likely to be key. DNA methylation can be modified by many environmental exposures and is dramatically altered in cancers, including childhood ALL. Here we explore the potential that DNA methylation may be involved in the causal pathway toward disease by acting as a mediator between established environmental factors and childhood ALL development.

New and emerging prognostic and predictive genetic biomarkers in B-cell precursor acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a heterogeneous disease at the genetic level. Chromosomal abnormalities are used as diagnostic, prognostic and predictive biomarkers to provide subtype, outcome and drug response information. t(12;21)/ETV6-RUNX1 and high hyper-diploidy are good-risk prognostic biomarkers whereas KMT2A(MLL) translocations, t(17;19)/TCF3-HLF, haploidy or low hypodiploidy are high-risk biomarkers. t(9;22)/BCR-ABL1 patients require targeted treatment (imatinib/dasatinib), whereas iAMP21 patients achieve better outcomes when treated intensively. High-risk genetic biomarkers are four times more prevalent in adults compared to children. The application of genomic technologies to cases without an established abnormality (B-other) reveals copy number alterations which can be used either individually or in combination as prognostic biomarkers. Transcriptome sequencing studies have identified a network of fusion genes involving kinase genes -ABL1,ABL2,PDGFRB,CSF1R,CRLF2,JAK2 and EPOR in-vitro and in-vivo studies along with emerging clinical observations indicate that patients with a kinase-activating aberration may respond to treatment with small molecular inhibitors like imatinib/dasatinib and ruxolitinib. Further work is required to determine the true frequency of these abnormalities across the age spectrum and the optimal way to incorporate such inhibitors into protocols. In conclusion, genetic biomarkers are playing an increasingly important role in the management of patients with ALL.

Caesarean delivery and risk of childhood leukaemia: a pooled analysis from the Childhood Leukemia International Consortium (CLIC)

BACKGROUND

Results from case-control studies have shown an increased risk of acute lymphoblastic leukaemia (ALL) in young children born by caesarean delivery, and prelabour caesarean delivery in particular; however, an association of method of delivery with childhood leukaemia subtypes has yet to be established. We therefore did a pooled analysis of data to investigate the association between childhood leukaemia and caesarean delivery.

METHODS

We pooled data from 13 case-control studies from the Childhood Leukemia International Consortium done in nine countries (Canada, Costa Rica, Egypt, France, Germany, Greece, Italy, New Zealand, and the USA) for births from 1970-2013. We analysed caesarean delivery overall and by indications that probably resulted in prelabour caesarean delivery or emergency caesarean delivery. We used multivariable logistic regression models, adjusted for child's birthweight, sex, age, ethnic origin, parental education, maternal age, and study, to estimate odds ratios (ORs) and 95% CIs for the risk of ALL and acute myeloid leukaemia (AML) in children aged 0-14 years at diagnosis.

FINDINGS

The studies provided data for 8780 ALL cases, 1332 AML cases, and 23 459 controls, of which the birth delivery method was known for 8655 (99%) ALL cases, 1292 (97%) AML cases, and 23 351 (>99%) controls. Indications for caesarean delivery were available in four studies (there were caesarean deliveries for 1061 of 4313 ALL cases, 138 of 664 AML cases, and 1401 of 5884 controls). The OR for all indications of caesarean delivery and ALL was 1·06 (95% CI 0·99-1·13), and was significant for prelabour caesarean delivery and ALL (1·23 [1·04-1·47]; p=0·018). Emergency caesarean delivery was not associated with ALL (OR 1·02 [95% CI 0·81-1·30]). AML was not associated with caesarean delivery (all indications OR 0·99 [95% CI 0·84-1·17]; prelabour caesarean delivery 0·83 [0·54-1·26]; and emergency caesarean delivery 1·05 [0·63-1·77]).

INTERPRETATION

Our results suggest an increased risk of childhood ALL after prelabour caesarean delivery. If this association is causal, maladaptive immune activation due to an absence of stress response before birth in children born by prelabour caesarean delivery could be considered as a potential mechanism.

FUNDING

National Cancer Institute.

The Natural History of Human Polyomaviruses and Herpesviruses in Early Life--The Rhea Birth Cohort in Greece

Sparse data exist on the patterns and determinants of acquisition of polyomaviruses and herpesviruses in childhood. We measured immunoglobulin G seroreactivity against 10 polyomaviruses (BKPyV, JCPyV, KIPyV, WUPyV, MCPyV, HPyV6, HPyV7, TSPyV, HPyV9, HPyV10) and 5 herpesviruses (Epstein Barr virus (EBV), cytomegalovirus (CMV), herpes simplex virus types 1 and 2, human herpesvirus 8) using multiplex serology on blood samples collected at birth (cord blood, n = 626) and at follow-up at 3 years (n = 81) and 4 years (n = 690) of age among the Rhea birth cohort recruited in Greece from pregnant women in 2007-2008. We used Poisson regression with robust variance to identify determinants of seropositivity at age 4. Seroprevalence of polyomaviruses ranged from 38.5% to 99.8% in cord blood and from 20.9% to 82.3% at age 4. Seroprevalence of EBV, CMV, herpes simplex virus types 1 and 2, and human herpesvirus 8 was 99.4%, 74.9%, 26.2%, 8.0%, and 1.6% in cord blood and 52.5%, 25.8%, 3.6%, 1.4%, and 0% at age 4, respectively. Determinants of seropositivity at age 4 were cord seropositivity (JCPyV, HPyV7, HPyV10, CMV), vaginal delivery (HPyV10), breastfeeding (CMV), younger age at day-care entry (BKPyV, KIPyV, WUPyV, TSPyV, HPyV10, HPyV9, EBV, CMV), and swimming pool attendance (BKPyV, KIPyV, WUPyV, HPyV10). Television viewing, parental stress, and hygiene practices were inversely associated with the seroprevalence of polyomaviruses and herpesviruses.

Linking Pesticide Exposure with Pediatric Leukemia: Potential Underlying Mechanisms

Leukemia is the most common cancer in children, representing 30% of all childhood cancers. The disease arises from recurrent genetic insults that block differentiation of hematopoietic stem and/or progenitor cells (HSPCs) and drives uncontrolled proliferation and survival of the differentiation-blocked clone. Pediatric leukemia is phenotypically and genetically heterogeneous with an obscure etiology. The interaction between genetic factors and environmental agents represents a potential etiological driver. Although information is limited, the principal toxic mechanisms of potential leukemogenic agents (e.g., etoposide, benzene metabolites, bioflavonoids and some pesticides) include topoisomerase II inhibition and/or excessive generation of free radicals, which may induce DNA single- and double-strand breaks (DNA-DSBs) in early HSPCs. Chromosomal rearrangements (duplications, deletions and translocations) may occur if these lesions are not properly repaired. The initiating hit usually occurs in utero and commonly leads to the expression of oncogenic fusion proteins. Subsequent cooperating hits define the disease latency and occur after birth and may be of a genetic, epigenetic or immune nature (i.e., delayed infection-mediated immune deregulation). Here, we review the available experimental and epidemiological evidence linking pesticide exposure to infant and childhood leukemia and provide a mechanistic basis to support the association, focusing on early initiating molecular events.

Potential for bispecific T-cell engagers: role of blinatumomab in acute lymphoblastic leukemia

Patients with relapsed/refractory (R/R) B-precursor acute lymphoblastic leukemia (ALL) and patients whose minimal residual disease persists during treatment have a poor leukemia-free survival. Despite improvements in front-line therapy, the outcome in these patients remains poor, especially after relapse. As there are no standard chemotherapeutic regimens for the treatment of patients with R/R B-precursor ALL, T-cell-based therapeutic approaches have recently come to the forefront in ALL therapy. Recently, monoclonal antibodies have been developed to target specific antigens expressed in B-lineage blast cells. In this setting, CD19 is of great interest as this antigen is expressed in B-lineage cells. Therefore, it has been selected as the target antigen for blinatumomab, a new bi-specific T-cell engager antibody. This sophisticated antibody binds sites for both CD19 and CD3, leading to T-cell proliferation and activation and B-cell apoptosis. Owing to its short serum half-life, blinatumomab has been administrated by continuous intravenous infusion with a favorable safety profile. The most significant toxicities were central nervous system events and the cytokine release syndrome. This new therapeutic approach using blinatumomab has been shown to be effective in patients with positive minimal residual disease and in patients with R/R B-precursor ALL leading to a recent approval by the US Food and Drug Administration after an accelerated review process. This review focuses on the profile of blinatumomab and its efficacy and safety.

Relationship between paediatric CT scans and subsequent risk of leukaemia and brain tumours: assessment of the impact of underlying conditions

BACKGROUND

We previously reported evidence of a dose-response relationship between ionising-radiation exposure from paediatric computed tomography (CT) scans and the risk of leukaemia and brain tumours in a large UK cohort. Underlying unreported conditions could have introduced bias into these findings.

METHODS

We collected and reviewed additional clinical information from radiology information systems (RIS) databases, underlying cause of death and pathology reports. We conducted sensitivity analyses excluding participants with cancer-predisposing conditions or previous unreported cancers and compared the dose-response analyses with our original results.

RESULTS

We obtained information from the RIS and death certificates for about 40% of the cohort (n∼180 000) and found cancer-predisposing conditions in 4 out of 74 leukaemia/myelodysplastic syndrome (MDS) cases and 13 out of 135 brain tumour cases. As these conditions were unrelated to CT exposure, exclusion of these participants did not alter the dose-response relationships. We found evidence of previous unreported cancers in 2 leukaemia/MDS cases, 7 brain tumour cases and 232 in non-cases. These previous cancers were related to increased number of CTs. Exclusion of these cancers reduced the excess relative risk per mGy by 15% from 0.036 to 0.033 for leukaemia/MDS (P-trend=0.02) and by 30% from 0.023 to 0.016 (P-trend<0.0001) for brain tumours. When we included pathology reports we had additional clinical information for 90% of the cases. Additional exclusions from these reports further reduced the risk estimates, but this sensitivity analysis may have underestimated risks as reports were only available for cases.

CONCLUSIONS

Although there was evidence of some bias in our original risk estimates, re-analysis of the cohort with additional clinical data still showed an increased cancer risk after low-dose radiation exposure from CT scans in young patients.

Reported associations between asthma and acute lymphoblastic leukemia: insights from a hybrid simulation study

Numerous studies have reported a protective association between asthma and acute lymphoblastic leukemia (ALL), but the causal structure of this association remains unclear. We present a hybrid simulation to examine the compatibility of this association with uncontrolled confounding by infection or another unmeasured factor. We generated a synthetic cohort using inputs on the interrelations of asthma, ALL, infections, and other suggested risk factors from the literature and the Danish National Birth Cohort. We computed odds ratios (ORs) between asthma and ALL in the synthetic cohort with and without adjustment for infections and other (including unmeasured) confounders. Only if infection was an extremely strong risk factor for asthma (OR of 10) and an extremely strong protective factor against ALL (OR of 0.1) was the asthma-ALL association compatible with the literature (OR of 0.78). Similarly, strong uncontrolled confounding by an unmeasured factor could downwardly bias the asthma-ALL association, but not enough to replicate findings in the literature. This investigation illustrates that the reported protective association between asthma and ALL is unlikely to be entirely due to uncontrolled confounding by infections or an unmeasured confounder alone. Simulation can be used to advance our understanding of risk factors for rare outcomes as demonstrated by this study.

Stochastic modeling reveals an evolutionary mechanism underlying elevated rates of childhood leukemia

Young children have higher rates of leukemia than young adults. This fact represents a fundamental conundrum, because hematopoietic cells in young children should have fewer mutations (including oncogenic ones) than such cells in adults. Here, we present the results of stochastic modeling of hematopoietic stem cell (HSC) clonal dynamics, which demonstrated that early HSC pools were permissive to clonal evolution driven by drift. We show that drift-driven clonal expansions cooperate with faster HSC cycling in young children to produce conditions that are permissive for accumulation of multiple driver mutations in a single cell. Later in life, clonal evolution was suppressed by stabilizing selection in the larger young adult pools, and it was driven by positive selection at advanced ages in the presence of microenvironmental decline. Overall, our results indicate that leukemogenesis is driven by distinct evolutionary forces in children and adults.

Space-time clustering of childhood cancers in Switzerland: A nationwide study

The aetiology of childhood cancers remains largely unknown. It has been hypothesized that infections may be involved and that mini-epidemics thereof could result in space-time clustering of incident cases. Most previous studies support spatio-temporal clustering for leukaemia, while results for other diagnostic groups remain mixed. Few studies have corrected for uneven regional population shifts which can lead to spurious detection of clustering. We examined whether there is space-time clustering of childhood cancers in Switzerland identifying cases diagnosed at age <16 years between 1985 and 2010 from the Swiss Childhood Cancer Registry. Knox tests were performed on geocoded residence at birth and diagnosis separately for leukaemia, acute lymphoid leukaemia (ALL), lymphomas, tumours of the central nervous system, neuroblastomas and soft tissue sarcomas. We used Baker's Max statistic to correct for multiple testing and randomly sampled time-, sex- and age-matched controls from the resident population to correct for uneven regional population shifts. We observed space-time clustering of childhood leukaemia at birth (Baker's Max p = 0.045) but not at diagnosis (p = 0.98). Clustering was strongest for a spatial lag of <1 km and a temporal lag of <2 years (Observed/expected close pairs: 124/98; p Knox test = 0.003). A similar clustering pattern was observed for ALL though overall evidence was weaker (Baker's Max p = 0.13). Little evidence of clustering was found for other diagnostic groups (p > 0.2). Our study suggests that childhood leukaemia tends to cluster in space-time due to an etiologic factor present in early life.

Molecular epidemiology of acute leukemia in children: causal model, interaction of three factors-susceptibility, environmental exposure and vulnerability period

Acute leukemias have a huge morphological, cytogenetic and molecular heterogeneity and genetic polymorphisms associated with susceptibility. Every leukemia presents causal factors associated with the development of the disease. Particularly, when three factors are present, they result in the development of acute leukemia. These phenomena are susceptibility, environmental exposure and a period that, for this model, has been called the period of vulnerability. This framework shows how the concepts of molecular epidemiology have established a reference from which it is more feasible to identify the environmental factors associated with the development of leukemia in children. Subsequently, the arguments show that only susceptible children are likely to develop leukemia once exposed to an environmental factor. For additional exposure, if the child is not susceptible to leukemia, the disease does not develop. In addition, this exposure should occur during a time window when hematopoietic cells and their environment are more vulnerable to such interaction, causing the development of leukemia. This model seeks to predict the time when the leukemia develops and attempts to give a context in which the causality of childhood leukemia should be studied. This information can influence and reduce the risk of a child developing leukemia.

Determinants of the t(14;18) translocation and their role in t(14;18)-positive follicular lymphoma

PURPOSE

The strong association between t(14;18) translocation and follicular lymphoma (FL) is well known. However, the determinants of this chromosomal aberration and their role in t(14;18) associated FL remain to be established.

METHODS

t(14;18) frequency within the B cell lymphoma 2 major breakpoint region was determined for 135 incident FL cases and 251 healthy controls as part of a nested case-control study within the European Prospective Investigation into Cancer cohort. Quantitative real-time PCR was performed in DNA extracted from blood samples taken at recruitment. The relationship between prevalence and frequency of the translocation with baseline anthropometric, lifestyle, and dietary factors in cases and controls was determined. Unconditional logistic regression was used to explore whether the risk of FL associated with these factors differed in t(14;18)(+) as compared to t(14;18)(-) cases.

RESULTS

Among incident FL cases, educational level (χ(2) p = 0.021) and height (χ(2) p = 0.025) were positively associated with t(14;18) prevalence, and cases with high frequencies [t(14;18)(HF)] were significantly taller (t test p value = 0.006). These findings were not replicated in the control population, although there were a number of significant associations with dietary variables. Further analyses revealed that height was a significant risk factor for t(14;18)(+) FL [OR 6.31 (95% CI 2.11, 18.9) in the tallest versus the shortest quartile], but not t(14;18)(-) cases.

CONCLUSIONS

These findings suggest a potential role for lifestyle factors in the prevalence and frequency of the t(14;18) translocation. The observation that the etiology of FL may differ by t(14;18) status, particularly with regard to height, supports the subdivision of FL by translocation status.

Germline genetic variation in ETV6 and risk of childhood acute lymphoblastic leukaemia: a systematic genetic study

BACKGROUND

Hereditary predisposition is rarely suspected for childhood acute lymphoblastic leukaemia (ALL). Recent reports of germline ETV6 variations associated with substantial familial clustering of haematological malignancies indicated that this gene is a potentially important genetic determinant for ALL susceptibility. Our aims in this study were to comprehensively identify ALL predisposition variants in ETV6 and to determine the extent to which they contributed to the overall risk of childhood ALL.

METHODS

Whole-exome sequencing of an index family with several cases of ALL was done to identify causal variants for ALL predisposition. Targeted sequencing of ETV6 was done in children from the Children's Oncology Group and St Jude Children's Research Hospital front-line ALL trials. Patients were included in this study on the basis of their enrolment in these clinical trials and the availability of germline DNA. ETV6 variant genotypes were compared with non-ALL controls to define ALL-related germline risk variants. ETV6 variant function was characterised bioinformatically and correlated with clinical and demographic features in children with ALL.

FINDINGS

We identified a novel non-sense ETV6 variant (p.Arg359X) with a high penetrance in an index family. Subsequent targeted sequencing of ETV6 in 4405 childhood ALL cases identified 31 exonic variants (four non-sense, 21 missense, one splice site, and five frameshift variants) that were potentially related to ALL risk in 35 cases (1%). 15 (48%) of 31 ALL-related ETV6 variants clustered in the erythroblast transformation specific domain and were predicted to be highly deleterious. Children with ALL-related ETV6 variants were significantly older at leukaemia diagnosis than those without (10·2 years [IQR 5·3-13·8] vs 4·7 years [3·0-8·7]; p=0·017). The hyperdiploid leukaemia karyotype was highly over-represented in ALL cases harbouring germline ETV6 risk variants compared with the wild-type group (nine [64%] of 14 cases vs 538 [27%] of 2007 cases; p=0·0050).

INTERPRETATION

Our findings indicated germline ETV6 variations as the basis of a novel genetic syndrome associated with predisposition to childhood ALL. The development of recommendations for clinical interventions and surveillance for individuals harbouring ALL-related ETV6 variants are needed.

FUNDING

US National Institutes of Health and American Lebanese Syrian Associated Charities.

Infection and the Perils of B-cell Activation

Recent studies have linked aberrant B-cell activation in the context of aberrant immune responses to infectious pathogens to malignant transformation and development of leukemia and lymphoma. A new study in this issue demonstrates that common infections can be drivers of clonal evolution of premalignant B-cell precursors toward childhood leukemia.

A Heritable Missense Polymorphism in CDKN2A Confers Strong Risk of Childhood Acute Lymphoblastic Leukemia and Is Preferentially Selected during Clonal Evolution

Genome-wide association studies (GWAS) have identified SNPs in six genes that are associated with childhood acute lymphoblastic leukemia (ALL). A lead SNP was found to occur on chromosome 9p21.3, a region that is deleted in 30% of childhood ALLs, suggesting the presence of causal polymorphisms linked to ALL risk. We used SNP genotyping and imputation-based fine-mapping of a multiethnic ALL case-control population (Ncases = 1,464, Ncontrols = 3,279) to identify variants of large effect within 9p21.3. We identified a CDKN2A missense variant (rs3731249) with 2% allele frequency in controls that confers three-fold increased risk of ALL in children of European ancestry (OR, 2.99; P = 1.51 × 10(-9)) and Hispanic children (OR, 2.77; P = 3.78 × 10(-4)). Moreover, of 17 patients whose tumors displayed allelic imbalance at CDKN2A, 14 preferentially retained the risk allele and lost the protective allele (PBinomial = 0.006), suggesting that the risk allele provides a selective advantage during tumor growth. Notably, the CDKN2A variant was not significantly associated with melanoma, glioblastoma, or pancreatic cancer risk, implying that this polymorphism specifically confers ALL risk but not general cancer risk. Taken together, our findings demonstrate that coding polymorphisms of large effect can underlie GWAS "hits" and that inherited polymorphisms may undergo directional selection during clonal expansion of tumors.

Aging-associated inflammation promotes selection for adaptive oncogenic events in B cell progenitors

The incidence of cancer is higher in the elderly; however, many of the underlying mechanisms for this association remain unexplored. Here, we have shown that B cell progenitors in old mice exhibit marked signaling, gene expression, and metabolic defects. Moreover, B cell progenitors that developed from hematopoietic stem cells (HSCs) transferred from young mice into aged animals exhibited similar fitness defects. We further demonstrated that ectopic expression of the oncogenes BCR-ABL, NRAS(V12), or Myc restored B cell progenitor fitness, leading to selection for oncogenically initiated cells and leukemogenesis specifically in the context of an aged hematopoietic system. Aging was associated with increased inflammation in the BM microenvironment, and induction of inflammation in young mice phenocopied aging-associated B lymphopoiesis. Conversely, a reduction of inflammation in aged mice via transgenic expression of α-1-antitrypsin or IL-37 preserved the function of B cell progenitors and prevented NRAS(V12)-mediated oncogenesis. We conclude that chronic inflammatory microenvironments in old age lead to reductions in the fitness of B cell progenitor populations. This reduced progenitor pool fitness engenders selection for cells harboring oncogenic mutations, in part due to their ability to correct aging-associated functional defects. Thus, modulation of inflammation--a common feature of aging--has the potential to limit aging-associated oncogenesis.

Childhood cancer and residential exposure to highways: a nationwide cohort study

Children living near highways are exposed to higher concentrations of traffic-related carcinogenic pollutants. Several studies reported an increased risk of childhood cancer associated with traffic exposure, but the published evidence is inconclusive. We investigated whether cancer risk is associated with proximity of residence to highways in a nation-wide cohort study including all children aged <16 years from Swiss national censuses in 1990 and 2000. Cancer incidence was investigated in time to event analyses (1990-2008) using Cox proportional hazards models and incidence density analyses (1985-2008) using Poisson regression. Adjustments were made for socio-economic factors, ionising background radiation and electromagnetic fields. In time to event analysis based on 532 cases the adjusted hazard ratio for leukaemia comparing children living <100 m from a highway with unexposed children (≥500 m) was 1.43 (95 % CI 0.79, 2.61). Results were similar in incidence density analysis including 1367 leukaemia cases (incidence rate ratio (IRR) 1.57; 95 % CI 1.09, 2.25). Associations were similar for acute lymphoblastic leukaemia (IRR 1.64; 95 % CI 1.10, 2.43) and stronger for leukaemia in children aged <5 years (IRR 1.92; 95 % CI 1.22, 3.04). Little evidence of association was found for other tumours. Our study suggests that young children living close to highways are at increased risk of developing leukaemia.

Birth order and risk of childhood cancer in the Danish birth cohort of 1973-2010

PURPOSE

Many studies have investigated the possible association between birth order and risk of childhood cancer, although the evidence to date has been inconsistent. Birth order has been used as a marker for various in utero or childhood exposures and is relatively straightforward to assess.

METHODS

Data were obtained on all children born in Denmark between 1973 and 2010, involving almost 2.5 million births and about 5,700 newly diagnosed childhood cancers before the age of 20 years. Data were analyzed using Poisson regression models.

RESULTS

We failed to observe associations between birth order and risk of any childhood cancer subtype, including acute lymphoblastic leukemia; all rate ratios were close to one. Further analyses stratified by birth cohort (those born between 1973 and 1990, and those born between 1991 and 2010) also failed to show any associations. Considering stillbirths and/or controlling for birth weight and parental age in the analyses had no effect on the results. Analyses by years of birth (those born between 1973 and 1990, and those born between 1991 and 2010) did not show any changes in the overall pattern of no association.

CONCLUSIONS

In this large cohort of all children born in Denmark over an almost 40-year period, we did not observe an association between birth order and the risk of childhood cancer.

Revisiting the biology of infant t(4;11)/MLL-AF4+ B-cell acute lymphoblastic leukemia

Infant B-cell acute lymphoblastic leukemia (B-ALL) accounts for 10% of childhood ALL. The genetic hallmark of most infant B-ALL is chromosomal rearrangements of the mixed-lineage leukemia (MLL) gene. Despite improvement in the clinical management and survival (∼85-90%) of childhood B-ALL, the outcome of infants with MLL-rearranged (MLL-r) B-ALL remains dismal, with overall survival <35%. Among MLL-r infant B-ALL, t(4;11)+ patients harboring the fusion MLL-AF4 (MA4) display a particularly poor prognosis and a pro-B/mixed phenotype. Studies in monozygotic twins and archived blood spots have provided compelling evidence of a single cell of prenatal origin as the target for MA4 fusion, explaining the brief leukemia latency. Despite its aggressiveness and short latency, current progress on its etiology, pathogenesis, and cellular origin is limited as evidenced by the lack of mouse/human models recapitulating the disease phenotype/latency. We propose this is because infant cancer is from an etiologic and pathogenesis standpoint distinct from adult cancer and should be seen as a developmental disease. This is supported by whole-genome sequencing studies suggesting that opposite to the view of cancer as a "multiple-and-sequential-hit" model, t(4;11) alone might be sufficient to spawn leukemia. The stable genome of these patients suggests that, in infant developmental cancer, one "big-hit" might be sufficient for overt disease and supports a key contribution of epigenetics and a prenatal cell of origin during a critical developmental window of stem cell vulnerability in the leukemia pathogenesis. Here, we revisit the biology of t(4;11)+ infant B-ALL with an emphasis on its origin, genetics, and disease models.

Children's Cancer and Environmental Exposures: Professional Attitudes and Practices

BACKGROUND

Epidemiologic studies worldwide have provided substantial evidence of the contributions of environmental exposures to the development of childhood cancer, yet this knowledge has not been integrated into the routine practice of clinicians who care for children with this disease. To identify the basis of this deficit, we sought to assess the environmental history-taking behavior and perceptions of environmental health among pediatric hematologists and oncologists.

PROCEDURE

A web-based survey was sent from June to October 2012 to 427 pediatric oncologists, fellows, and nurse practitioners from 20 US institutions, with an overall response rate of 45%.

RESULTS

Survey responses indicated that environmental exposures are of concern to clinicians. The vast majority of respondents (88%) reported receiving questions from families about the relationship between certain environmental exposures and the cancers they regularly treat. However, a lack of comfort with these topics seems to have limited their discussions with families about the role of environmental exposures in childhood cancer pathogenesis. Although 77% of respondents suspected that some of the cases they saw had an environmental origin, their methods of taking environmental histories varied widely. Over 90% of respondents believed that more knowledge of the associations between environmental exposures and childhood cancer would be helpful in addressing these issues with patients.

CONCLUSIONS

Although limited in size and representativeness of participating institutions, the results of this survey indicate a need for increased training for hematology/oncology clinicians about environmental health exposures related to cancer and prompt translation of emerging research findings in biomedical journals that clinicians read.

Infection Exposure is a Causal Factor in B-cell Precursor Acute Lymphoblastic Leukemia as a Result of Pax5-Inherited Susceptibility

Earlier in the past century, infections were regarded as the most likely cause of childhood B-cell precursor acute lymphoblastic leukemia (pB-ALL). However, there is a lack of relevant biologic evidence supporting this hypothesis. We present in vivo genetic evidence mechanistically connecting inherited susceptibility to pB-ALL and postnatal infections by showing that pB-ALL was initiated in Pax5 heterozygous mice only when they were exposed to common pathogens. Strikingly, these murine pB-ALLs closely resemble the human disease. Tumor exome sequencing revealed activating somatic, nonsynonymous mutations of Jak3 as a second hit. Transplantation experiments and deep sequencing suggest that inactivating mutations in Pax5 promote leukemogenesis by creating an aberrant progenitor compartment that is susceptible to malignant transformation through accumulation of secondary Jak3 mutations. Thus, treatment of Pax5(+/-) leukemic cells with specific JAK1/3 inhibitors resulted in increased apoptosis. These results uncover the causal role of infection in pB-ALL development.

SIGNIFICANCE

These results demonstrate that delayed infection exposure is a causal factor in pB-ALL. Therefore, these findings have critical implications for the understanding of the pathogenesis of leukemia and for the development of novel therapies for this disease.

Early-life exposures to infectious agents and later cancer development

There is a growing understanding that several infectious agents are acquired in early life and this is the reason why available vaccines target the new born, infants, and adolescents. Infectious agents are associated with cancer development and it is estimated that about 20% of the world's cancer burden is attributed to infectious agents. There is a growing evidence that certain infectious agents acquired in early life can give rise to cancer development, but estimates of the cancer burden from this early‐life acquisition is unknown. In this article, we have selected five cancers (cervical, liver, Burkitt's lymphoma‐leukemia, nasopharyngeal carcinoma, and adult T‐cell leukemia‐lymphoma) and examine their links to infectious agents (HPV, HBV, HCV, EBV, and HTLV‐1) acquired in early life. For these agents, the acquisition in early life is from mother‐to‐child transmission, perinatal contact (with genital tract secretions, amniotic fluids, blood, and breast milk), saliva, sexual intercourse, and blood transfusion. We also discuss prevention strategies, address future directions, and propose mechanisms of action after a long latency period from the time of acquisition of the infectious agent in early life to cancer development.

Home paint exposures and risk of childhood acute lymphoblastic leukemia: findings from the Childhood Leukemia International Consortium

PURPOSE

It has been suggested that home paint exposure increases the risk of childhood acute lymphoblastic leukemia (ALL).

METHODS

We obtained individual level data from eight case-control studies participating in the Childhood Leukemia International Consortium. All studies had home paint exposure data (sometimes including lacquers and varnishes) for the pregnancy period with additional data for the 1-3-month period before conception in five, the year before conception in two, and the period after birth in four studies, respectively. Cytogenetic subtype data were available for some studies. Data were harmonized to a compatible format. Pooled analyses of individual data were undertaken using unconditional logistic regression.

RESULTS

Based on 3,002 cases and 3,836 controls, the pooled odds ratio (OR) for home paint exposure in the 1-3 months before conception and risk of ALL was 1.54 [95% confidence interval (CI) 1.28, 1.85], while based on 1,160 cases and 1,641 controls for exposure in the year before conception, it was 1.00 (95% CI 0.86, 1.17). For exposure during pregnancy, using 4,382 cases and 5,747 controls, the pooled OR was 1.14 (95% CI 1.04, 1.25), and for exposure after birth, the OR was 1.22 (95% CI 1.07, 1.39), based on data from 1,962 cases and 2,973 controls. The risk was greater for certain cytogenetic subtypes and if someone other than the parents did the painting.

CONCLUSIONS

Home paint exposure shortly before conception, during pregnancy, and/or after birth appeared to increase the risk of childhood ALL. It may be prudent to limit exposure during these periods.

Evolutionary determinants of cancer

Our understanding of cancer is being transformed by exploring clonal diversity, drug resistance, and causation within an evolutionary framework. The therapeutic resilience of advanced cancer is a consequence of its character as a complex, dynamic, and adaptive ecosystem engendering robustness, underpinned by genetic diversity and epigenetic plasticity. The risk of mutation-driven escape by self-renewing cells is intrinsic to multicellularity but is countered by multiple restraints, facilitating increasing complexity and longevity of species. But our own species has disrupted this historical narrative by rapidly escalating intrinsic risk. Evolutionary principles illuminate these challenges and provide new avenues to explore for more effective control.

SIGNIFICANCE

Lifetime risk of cancer now approximates to 50% in Western societies. And, despite many advances, the outcome for patients with disseminated disease remains poor, with drug resistance the norm. An evolutionary perspective may provide a clearer understanding of how cancer clones develop robustness and why, for us as a species, risk is now off the scale. And, perhaps, of what we might best do to achieve more effective control.

Evolutionary determinants of cancer

Our understanding of cancer is being transformed by exploring clonal diversity, drug resistance, and causation within an evolutionary framework. The therapeutic resilience of advanced cancer is a consequence of its character as a complex, dynamic, and adaptive ecosystem engendering robustness, underpinned by genetic diversity and epigenetic plasticity. The risk of mutation-driven escape by self-renewing cells is intrinsic to multicellularity but is countered by multiple restraints, facilitating increasing complexity and longevity of species. But our own species has disrupted this historical narrative by rapidly escalating intrinsic risk. Evolutionary principles illuminate these challenges and provide new avenues to explore for more effective control.

SIGNIFICANCE

Lifetime risk of cancer now approximates to 50% in Western societies. And, despite many advances, the outcome for patients with disseminated disease remains poor, with drug resistance the norm. An evolutionary perspective may provide a clearer understanding of how cancer clones develop robustness and why, for us as a species, risk is now off the scale. And, perhaps, of what we might best do to achieve more effective control.

Viremia during pregnancy and risk of childhood leukemia and lymphomas in the offspring: Nested case-control study

A possible role for infections of the pregnant mother in the development of childhood acute leukemias and lymphomas has been suggested. However, no specific infectious agent has been identified. Offspring of 74,000 mothers who had serum samples taken during pregnancy and stored in a large-scale biobank were followed up to the age of 15 years (750,000 person years) through over-generation linkages between the biobank files, the Swedish national population and cancer registers to identify incident leukemia/lymphoma cases in the offspring. First-trimester sera from mothers of 47 cases and 47 matched controls were retrieved and analyzed using next generation sequencing. Anelloviruses were the most common viruses detected, found in 37/47 cases and in 40/47 controls, respectively (OR: 0.6, 95% CI: 0.2-1.9). None of the detected viruses was associated with leukemia/lymphoma in the offspring. Viremia during pregnancy was common, but no association with leukemia/lymphoma risk in the offspring was found.

Antibiotic use from conception to diagnosis of child leukaemia as compared to the background population: A nested case-control study

BACKGROUND

The role of infection in the aetiology of childhood leukaemia is unknown. We used prescriptions of antibiotics from Danish pharmacies as a proxy measure for the occurrence of infections.

PROCEDURE

We investigated the association between exposure to antibiotics, from conception to leukaemia diagnosis, and the risk of leukaemia. Incident cases of leukaemia among children in Denmark, 1995-2008, with mothers having their earliest conception date in 1995, were individually matched to population controls by age, sex and municipality. Conditional logistic regression analyses assessed antibiotic redemptions in different time periods from conception up to 6 months before the diagnoses of all leukaemia types, acute lymphoblastic leukaemia [ALL] and ALL in 2- to 5-year-old children, adjusting for several potential confounders.

RESULTS

A total of 120/360 (33.3%) leukaemia mothers and 1,081/3,509 (30.8%) control mothers redeemed antibiotics during pregnancy (P = 0.32). For children, the equivalent numbers were 276 (76.7%) and 2,665 (75.9%) (P = 0.76). Histograms of antibiotic redemptions showed no temporal differences between leukaemia mothers/children and controls, which was confirmed in adjusted regression analyses (OR [95% CI]: 1.02 [0.75-1.38]). Only antibiotics redeemed during the first year after birth differed from this (OR [95% CI] for ALL diagnosed in 2- to 5-year-old children: 0.46 [0.31-0.66]).

CONCLUSIONS

In this hypothesis generating study, the similar amount and pattern of antibiotic redemptions in children with and without leukaemia indicate that infections play a minor role in the aetiology of childhood leukaemia. However, less antibiotic redemptions during the first year of life conform to Greaves' 'delayed infection hypothesis'.

Mechanisms of clonal evolution in childhood acute lymphoblastic leukemia

Childhood acute lymphoblastic leukemia (ALL) can often be traced to a pre-leukemic clone carrying a prenatal genetic lesion. Postnatally acquired mutations then drive clonal evolution toward overt leukemia. The enzymes RAG1-RAG2 and AID, which diversify immunoglobulin-encoding genes, are strictly segregated in developing cells during B lymphopoiesis and peripheral mature B cells, respectively. Here we identified small pre-BII cells as a natural subset with increased genetic vulnerability owing to concurrent activation of these enzymes. Consistent with epidemiological findings on childhood ALL etiology, susceptibility to genetic lesions during B lymphopoiesis at the transition from the large pre-BII cell stage to the small pre-BII cell stage was exacerbated by abnormal cytokine signaling and repetitive inflammatory stimuli. We demonstrated that AID and RAG1-RAG2 drove leukemic clonal evolution with repeated exposure to inflammatory stimuli, paralleling chronic infections in childhood.

Inherited coding variants at the CDKN2A locus influence susceptibility to acute lymphoblastic leukaemia in children

There is increasing evidence from genome-wide association studies for a strong inherited genetic basis of susceptibility to acute lymphoblastic leukaemia (ALL) in children, yet the effects of protein-coding variants on ALL risk have not been systematically evaluated. Here we show a missense variant in CDKN2A associated with the development of ALL at genome-wide significance (rs3731249, P=9.4 × 10(-23), odds ratio=2.23). Functional studies indicate that this hypomorphic variant results in reduced tumour suppressor function of p16(INK4A), increases the susceptibility to leukaemic transformation of haematopoietic progenitor cells, and is preferentially retained in ALL tumour cells. Resequencing the CDKN2A-CDKN2B locus in 2,407 childhood ALL cases reveals 19 additional putative functional germline variants. These results provide direct functional evidence for the influence of inherited genetic variation on ALL risk, highlighting the important and complex roles of CDKN2A-CDKN2B tumour suppressors in leukaemogenesis.