Infections, vaccinations, and the risk of childhood leukaemia

Breastfeeding Duration Reduces the Risk of Childhood Leukemia and Modifies the Risk of Developing Functional Gastrointestinal Disorders

Objective: The aim of this study was to test the hypothesis that the duration of breastfeeding in infancy reduces the risk of childhood leukemia or lymphoma, and modifies the risk of developing functional gastrointestinal disorders (FGIDs). Subjects and Methods: This case-control study involved the recruitment of children with lymphoid malignancy and functional gastrointestinal symptoms with healthy children as controls. Focused questionnaires were used to collect data on breastfeeding history and other key risk factors. Univariate and multivariate analyses were undertaken. Results: Of the 334 children with lymphoid malignancy, 65% were male. The control group included 334 age- and sex-matched participants. Most (n = 189; 56.6%) of the children with leukemia were <10 years of age. Differences between cases and controls included the duration of breastfeeding (p < 0.0001), mean birthweight (p < 0.001), maternal age (p < 0.001), paternal age (p < 0.001), birth order (p < 0.001), mean number of children (p < 0.001), BMI percentile (p = 0.042), and maternal smoking (p = 0.012). Breastfeeding duration of up to 6 months' duration, when compared with feeding of longer than 6 months, was associated with increased odds ratios (OR) for acute lymphoblastic leukemia (OR = 3.43, 95% confidence interval [CI] 2.37-4.98; p < 0.001), Hodgkin's lymphoma (OR = 1.58, 95% CI: 0.88-2.84, p = 0.120), Non-Hodgkin's lymphoma (OR = 2.14, 95% CI: 1.25-3.65, p = 0.005), and overall (OR = 1.95, 95% CI: 1.40-2.71, p < 0.001). Cases also differed from controls with regard to FGIDs, such as stomach ache (p < 0.001), dyspepsia (p < 0.001), early satiety (p = 0.017), bowel satisfaction (p < 0.001), bloating (p < 0.001), nausea (p = 0.005), vomiting (p = 0.039), constipation (p = 0.003), diarrhea (p = 0.010), gastrointestinal canal congestion (p =0.039), muscle aches pains (p = 0.008), fecal incontinence (p = 0.021), and indigestion (p = 0.003). A multivariate stepwise regression analysis revealed that maternal smoking (p < 0.001), formula feeding (p < 0.001), duration of breastfeeding (p < 0.001), birth order (p = 0.002), mother's age (p = 0.004) and the child's birthweight (p = 0.009) were predictors for leukemia. Further analysis showed that dyspepsia (p < 0.001), gastrointestinal tract canal congestion (p < 0.001), constipation (p = 0.009), diarrhea (p = 0.013), bowel satisfaction (p = 0.021), bloating (p = 0.022), duration of breastfeeding (p < 0.001), and stomach ache (p = 0.025) were significant predictors for developing FGID symptoms after adjusting for age, gender, and other confounding variables. Conclusion: This study confirmed that breastfeeding has some effect on reducing possible risk of childhood lymphoma and leukemia and FGID symptoms compared with healthy control children.

Evaluation of Maternal Infection During Pregnancy and Childhood Leukemia Among Offspring in Denmark

IMPORTANCE

Maternal infection is common during pregnancy and is an important potential cause of fetal genetic and immunological abnormalities. Maternal infection has been reported to be associated with childhood leukemia in previous case-control or small cohort studies.

OBJECTIVE

To evaluate the association of maternal infection during pregnancy with childhood leukemia among offspring in a large study.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study used data from 7 Danish national registries (including the Danish Medical Birth Register, the Danish National Patient Registry, the Danish National Cancer Registry, and others) for all live births in Denmark between 1978 and 2015. Swedish registry data for all live births between 1988 and 2014 were used to validate the findings for the Danish cohort. Data were analyzed from December 2019 to December 2021.

EXPOSURES

Maternal infection during pregnancy categorized by anatomic locations identified from the Danish National Patient Registry.

MAIN OUTCOMES AND MEASURES

The primary outcome was any leukemia; secondary outcomes were acute lymphoid leukemia (ALL) and acute myeloid leukemia (AML). Offspring childhood leukemia was identified in the Danish National Cancer Registry. Associations were first assessed in the whole cohort using Cox proportional hazards regression models, adjusted for potential confounders. A sibling analysis was performed to account for unmeasured familial confounding.

RESULTS

This study included 2 222 797 children, 51.3% of whom were boys. During the approximately 27 million person-years of follow-up (mean [SD], 12.0 [4.6] years per person), 1307 children were diagnosed with leukemia (ALL, 1050; AML, 165; or other, 92). Children born to mothers with infection during pregnancy had a 35% increased risk of leukemia (adjusted hazard ratio [HR], 1.35 [95% CI, 1.04-1.77]) compared with offspring of mothers without infection. Maternal genital and urinary tract infections were associated with a 142% and 65% increased risk of childhood leukemia, with HRs of 2.42 (95% CI, 1.50-3.92) and 1.65 (95% CI, 1.15-2.36), respectively. No association was observed for respiratory tract, digestive, or other infections. The sibling analysis showed comparable estimates to the whole-cohort analysis. The association patterns for ALL and AML were similar to that for any leukemia. No association was observed for maternal infection and brain tumors, lymphoma, or other childhood cancers.

CONCLUSIONS AND RELEVANCE

In this cohort study of approximately 2.2 million children, maternal genitourinary tract infection during pregnancy was associated with childhood leukemia among offspring. If confirmed in future studies, our findings may have implications for understanding the etiology and developing preventive measures for childhood leukemia.

Vaccines for measles, mumps, rubella, and varicella in children

BACKGROUND

Measles, mumps, rubella, and varicella (chickenpox) are serious diseases that can lead to serious complications, disability, and death. However, public debate over the safety of the trivalent MMR vaccine and the resultant drop in vaccination coverage in several countries persists, despite its almost universal use and accepted effectiveness. This is an update of a review published in 2005 and updated in 2012.

OBJECTIVES

To assess the effectiveness, safety, and long- and short-term adverse effects associated with the trivalent vaccine, containing measles, rubella, mumps strains (MMR), or concurrent administration of MMR vaccine and varicella vaccine (MMR+V), or tetravalent vaccine containing measles, rubella, mumps, and varicella strains (MMRV), given to children aged up to 15 years.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2019, Issue 5), which includes the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to 2 May 2019), Embase (1974 to 2 May 2019), the WHO International Clinical Trials Registry Platform (2 May 2019), and ClinicalTrials.gov (2 May 2019).

SELECTION CRITERIA

We included randomised controlled trials (RCTs), controlled clinical trials (CCTs), prospective and retrospective cohort studies (PCS/RCS), case-control studies (CCS), interrupted time-series (ITS) studies, case cross-over (CCO) studies, case-only ecological method (COEM) studies, self-controlled case series (SCCS) studies, person-time cohort (PTC) studies, and case-coverage design/screening methods (CCD/SM) studies, assessing any combined MMR or MMRV / MMR+V vaccine given in any dose, preparation or time schedule compared with no intervention or placebo, on healthy children up to 15 years of age.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed the methodological quality of the included studies. We grouped studies for quantitative analysis according to study design, vaccine type (MMR, MMRV, MMR+V), virus strain, and study settings. Outcomes of interest were cases of measles, mumps, rubella, and varicella, and harms. Certainty of evidence of was rated using GRADE.

MAIN RESULTS

We included 138 studies (23,480,668 participants). Fifty-one studies (10,248,159 children) assessed vaccine effectiveness and 87 studies (13,232,509 children) assessed the association between vaccines and a variety of harms. We included 74 new studies to this 2019 version of the review. Effectiveness Vaccine effectiveness in preventing measles was 95% after one dose (relative risk (RR) 0.05, 95% CI 0.02 to 0.13; 7 cohort studies; 12,039 children; moderate certainty evidence) and 96% after two doses (RR 0.04, 95% CI 0.01 to 0.28; 5 cohort studies; 21,604 children; moderate certainty evidence). The effectiveness in preventing cases among household contacts or preventing transmission to others the children were in contact with after one dose was 81% (RR 0.19, 95% CI 0.04 to 0.89; 3 cohort studies; 151 children; low certainty evidence), after two doses 85% (RR 0.15, 95% CI 0.03 to 0.75; 3 cohort studies; 378 children; low certainty evidence), and after three doses was 96% (RR 0.04, 95% CI 0.01 to 0.23; 2 cohort studies; 151 children; low certainty evidence). The effectiveness (at least one dose) in preventing measles after exposure (post-exposure prophylaxis) was 74% (RR 0.26, 95% CI 0.14 to 0.50; 2 cohort studies; 283 children; low certainty evidence). The effectiveness of Jeryl Lynn containing MMR vaccine in preventing mumps was 72% after one dose (RR 0.24, 95% CI 0.08 to 0.76; 6 cohort studies; 9915 children; moderate certainty evidence), 86% after two doses (RR 0.12, 95% CI 0.04 to 0.35; 5 cohort studies; 7792 children; moderate certainty evidence). Effectiveness in preventing cases among household contacts was 74% (RR 0.26, 95% CI 0.13 to 0.49; 3 cohort studies; 1036 children; moderate certainty evidence).  Vaccine effectiveness against rubella, using a vaccine with the BRD2 strain which is only used in China, is 89% (RR 0.11, 95% CI 0.03 to 0.42; 1 cohort study; 1621 children; moderate certainty evidence).  Vaccine effectiveness against varicella (any severity) after two doses in children aged 11 to 22 months is 95% in a 10 years follow-up (rate ratio (rr) 0.05, 95% CI 0.03 to 0.08; 1 RCT; 2279 children; high certainty evidence). Safety There is evidence supporting an association between aseptic meningitis and MMR vaccines containing Urabe and Leningrad-Zagreb mumps strains, but no evidence supporting this association for MMR vaccines containing Jeryl Lynn mumps strains (rr 1.30, 95% CI 0.66 to 2.56; low certainty evidence). The analyses provide evidence supporting an association between MMR/MMR+V/MMRV vaccines (Jeryl Lynn strain) and febrile seizures. Febrile seizures normally occur in 2% to 4% of healthy children at least once before the age of 5. The attributable risk febrile seizures vaccine-induced is estimated to be from 1 per 1700 to 1 per 1150 administered doses. The analyses provide evidence supporting an association between MMR vaccination and idiopathic thrombocytopaenic purpura (ITP). However, the risk of ITP after vaccination is smaller than after natural infection with these viruses. Natural infection of ITP occur in 5 cases per 100,000 (1 case per 20,000) per year. The attributable risk is estimated about 1 case of ITP per 40,000 administered MMR doses. There is no evidence of an association between MMR immunisation and encephalitis or encephalopathy (rate ratio 0.90, 95% CI 0.50 to 1.61; 2 observational studies; 1,071,088 children; low certainty evidence), and autistic spectrum disorders (rate ratio 0.93, 95% CI 0.85 to 1.01; 2 observational studies; 1,194,764 children; moderate certainty). There is insufficient evidence to determine the association between MMR immunisation and inflammatory bowel disease (odds ratio 1.42, 95% CI 0.93 to 2.16; 3 observational studies; 409 cases and 1416 controls; moderate certainty evidence). Additionally, there is no evidence supporting an association between MMR immunisation and cognitive delay, type 1 diabetes, asthma, dermatitis/eczema, hay fever, leukaemia, multiple sclerosis, gait disturbance, and bacterial or viral infections.  AUTHORS' CONCLUSIONS: Existing evidence on the safety and effectiveness of MMR/MMRV vaccines support their use for mass immunisation. Campaigns aimed at global eradication should assess epidemiological and socioeconomic situations of the countries as well as the capacity to achieve high vaccination coverage. More evidence is needed to assess whether the protective effect of MMR/MMRV could wane with time since immunisation.

Breastfeeding and the risk of childhood cancer: a systematic review and dose-response meta-analysis

BACKGROUND

The aim of this study was to quantitatively summarize the available evidence on the association of breastfeeding with the risk of childhood cancer.

METHODS

A literature search of PubMed and Embase databases was performed to identify eligible observational studies published from inception to July 17, 2020. The categorical and dose-response meta-analysis was conducted by pooling relative risk (RR) or odds ratio (OR) estimates with 95% confidence intervals (CIs). Potential sources of heterogeneity were detected by meta-regression and stratification analysis. Sensitivity analysis and publication bias test were also carried out.

RESULTS

Forty-five articles involving 475,579 individuals were included in the meta-analysis. Among the thirty-three studies on the association between breastfeeding and risk of childhood leukemia, the pooled risk estimates were 0.77 (95% CI, 0.65-0.91) and 0.77 (95% CI 0.63-0.94) for ever versus non/occasional breastfeeding and longest versus shortest breastfeeding duration group, respectively. There was clear indication for non-linear dose-response relationship between breastfeeding duration and the risk of childhood leukemia (P non-linear < 0.001). The most protective effect (OR, 0.66, 95% CI 0.62-0.70) was observed at a breastfeeding duration of 9.6 months. Four studies examined, the association between breastfeeding and risk of childhood neuroblastoma, and significant inverse associations were consistently observed in both the comparisons of ever breastfeeding versus non/occasional breastfeeding (OR = 0.59, 95% CI 0.44-0.81) and longest versus shortest breastfeeding (OR = 0.61, 95% CI 0.44-0.83). However, no associations of breastfeeding with risk of other cancers were found.

CONCLUSIONS

Our study supports a protective role of breastfeeding on the risk of childhood leukemia, also suggesting a non-linear dose-response relationship. Further studies are warranted to confirm the association between breastfeeding and risk of childhood neuroblastoma.

Vaccination and the Risk of Childhood Cancer-A Systematic Review and Meta-Analysis

INTRODUCTION

Infections may play a role in the etiology of childhood cancer and immunizations may be protective because vaccinations stimulate the immune system. Observational studies reported inconsistent associations between vaccination and risk of childhood cancer. Since a synthesis of the evidence is lacking, we conducted a meta-analysis stratified by histological and site-specific cancer.

METHODS

We performed a systematic review (CRD42020148579) following PRISMA guidelines and searched for literature in MEDLINE, Embase, and the Science Citation Index databases. We identified in three literature databases 7,594 different articles of which 35 met the inclusion criteria allowing for 27 analyses of 11 cancer outcomes after exposure to nine different types of vaccinations. We calculated summary odds ratios (ORs) and 95% confidence intervals (CIs) using random effects models.

RESULTS

We observed four inverse associations between childhood leukemia and certain vaccines as well as the number of vaccinations: OR 0.49 (95% CI = 0.32 to 0.74) for leukemia death after bacillus Calmette-Guérin vaccination; OR 0.76 (95% CI = 0.65 to 0.90) for acute lymphoblastic leukemia after Haemophilus influenzae type b vaccination; OR 0.57 (95% CI = 0.36 to 0.88) for leukemia; and OR 0.62 (95% CI = 0.46 to 0.85) for acute lymphoblastic leukemia after three or more vaccinations of any type. All other conducted analyses did not show any associations.

DISCUSSION

The results are consistent with the hypothesis that vaccinations reduce the risk of childhood leukemia. However, the robustness and validity of these results is limited due to the small number, substantial heterogeneity, and methodological limitations of available studies.

History of Early Childhood Infections and Acute Lymphoblastic Leukemia Risk Among Children in a US Integrated Health-Care System

Surrogate measures of infectious exposures have been consistently associated with lower childhood acute lymphoblastic leukemia (ALL) risk. However, recent reports have suggested that physician-diagnosed early-life infections increase ALL risk, thereby raising the possibility that stronger responses to infections might promote risk. We examined whether medically diagnosed infections were related to childhood ALL risk in an integrated health-care system in the United States. Cases of ALL (n = 435) diagnosed between 1994-2014 among children aged 0-14 years, along with matched controls (n = 2,170), were identified at Kaiser Permanente Northern California. Conditional logistic regression was used to estimate risk of ALL associated with history of infections during first year of life and across the lifetime (up to diagnosis). History of infection during first year of life was not associated with ALL risk (odds ratio (OR) = 0.85, 95% confidence interval (CI): 0.60, 1.21). However, infections with at least 1 medication prescribed (i.e., more "severe" infections) were inversely associated with risk (OR = 0.42, 95% CI: 0.20, 0.88). Similar associations were observed when the exposure window was expanded to include medication-prescribed infections throughout the subjects' lifetime (OR = 0.52, 95% CI: 0.32, 0.85).

Vaccines for measles, mumps, rubella, and varicella in children

BACKGROUND

Measles, mumps, rubella, and varicella (chickenpox) are serious diseases that can lead to serious complications, disability, and death. However, public debate over the safety of the trivalent MMR vaccine and the resultant drop in vaccination coverage in several countries persists, despite its almost universal use and accepted effectiveness. This is an update of a review published in 2005 and updated in 2012.

OBJECTIVES

To assess the effectiveness, safety, and long- and short-term adverse effects associated with the trivalent vaccine, containing measles, rubella, mumps strains (MMR), or concurrent administration of MMR vaccine and varicella vaccine (MMR+V), or tetravalent vaccine containing measles, rubella, mumps, and varicella strains (MMRV), given to children aged up to 15 years.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2019, Issue 5), which includes the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to 2 May 2019), Embase (1974 to 2 May 2019), the WHO International Clinical Trials Registry Platform (2 May 2019), and ClinicalTrials.gov (2 May 2019).

SELECTION CRITERIA

We included randomised controlled trials (RCTs), controlled clinical trials (CCTs), prospective and retrospective cohort studies (PCS/RCS), case-control studies (CCS), interrupted time-series (ITS) studies, case cross-over (CCO) studies, case-only ecological method (COEM) studies, self-controlled case series (SCCS) studies, person-time cohort (PTC) studies, and case-coverage design/screening methods (CCD/SM) studies, assessing any combined MMR or MMRV / MMR+V vaccine given in any dose, preparation or time schedule compared with no intervention or placebo, on healthy children up to 15 years of age.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed the methodological quality of the included studies. We grouped studies for quantitative analysis according to study design, vaccine type (MMR, MMRV, MMR+V), virus strain, and study settings. Outcomes of interest were cases of measles, mumps, rubella, and varicella, and harms. Certainty of evidence of was rated using GRADE.

MAIN RESULTS

We included 138 studies (23,480,668 participants). Fifty-one studies (10,248,159 children) assessed vaccine effectiveness and 87 studies (13,232,509 children) assessed the association between vaccines and a variety of harms. We included 74 new studies to this 2019 version of the review. Effectiveness Vaccine effectiveness in preventing measles was 95% after one dose (relative risk (RR) 0.05, 95% CI 0.02 to 0.13; 7 cohort studies; 12,039 children; moderate certainty evidence) and 96% after two doses (RR 0.04, 95% CI 0.01 to 0.28; 5 cohort studies; 21,604 children; moderate certainty evidence). The effectiveness in preventing cases among household contacts or preventing transmission to others the children were in contact with after one dose was 81% (RR 0.19, 95% CI 0.04 to 0.89; 3 cohort studies; 151 children; low certainty evidence), after two doses 85% (RR 0.15, 95% CI 0.03 to 0.75; 3 cohort studies; 378 children; low certainty evidence), and after three doses was 96% (RR 0.04, 95% CI 0.01 to 0.23; 2 cohort studies; 151 children; low certainty evidence). The effectiveness (at least one dose) in preventing measles after exposure (post-exposure prophylaxis) was 74% (RR 0.26, 95% CI 0.14 to 0.50; 2 cohort studies; 283 children; low certainty evidence). The effectiveness of Jeryl Lynn containing MMR vaccine in preventing mumps was 72% after one dose (RR 0.24, 95% CI 0.08 to 0.76; 6 cohort studies; 9915 children; moderate certainty evidence), 86% after two doses (RR 0.12, 95% CI 0.04 to 0.35; 5 cohort studies; 7792 children; moderate certainty evidence). Effectiveness in preventing cases among household contacts was 74% (RR 0.26, 95% CI 0.13 to 0.49; 3 cohort studies; 1036 children; moderate certainty evidence). Vaccine effectiveness against rubella is 89% (RR 0.11, 95% CI 0.03 to 0.42; 1 cohort study; 1621 children; moderate certainty evidence). Vaccine effectiveness against varicella (any severity) after two doses in children aged 11 to 22 months is 95% in a 10 years follow-up (rate ratio (rr) 0.05, 95% CI 0.03 to 0.08; 1 RCT; 2279 children; high certainty evidence). Safety There is evidence supporting an association between aseptic meningitis and MMR vaccines containing Urabe and Leningrad-Zagreb mumps strains, but no evidence supporting this association for MMR vaccines containing Jeryl Lynn mumps strains (rr 1.30, 95% CI 0.66 to 2.56; low certainty evidence). The analyses provide evidence supporting an association between MMR/MMR+V/MMRV vaccines (Jeryl Lynn strain) and febrile seizures. Febrile seizures normally occur in 2% to 4% of healthy children at least once before the age of 5. The attributable risk febrile seizures vaccine-induced is estimated to be from 1 per 1700 to 1 per 1150 administered doses. The analyses provide evidence supporting an association between MMR vaccination and idiopathic thrombocytopaenic purpura (ITP). However, the risk of ITP after vaccination is smaller than after natural infection with these viruses. Natural infection of ITP occur in 5 cases per 100,000 (1 case per 20,000) per year. The attributable risk is estimated about 1 case of ITP per 40,000 administered MMR doses. There is no evidence of an association between MMR immunisation and encephalitis or encephalopathy (rate ratio 0.90, 95% CI 0.50 to 1.61; 2 observational studies; 1,071,088 children; low certainty evidence), and autistic spectrum disorders (rate ratio 0.93, 95% CI 0.85 to 1.01; 2 observational studies; 1,194,764 children; moderate certainty). There is insufficient evidence to determine the association between MMR immunisation and inflammatory bowel disease (odds ratio 1.42, 95% CI 0.93 to 2.16; 3 observational studies; 409 cases and 1416 controls; moderate certainty evidence). Additionally, there is no evidence supporting an association between MMR immunisation and cognitive delay, type 1 diabetes, asthma, dermatitis/eczema, hay fever, leukaemia, multiple sclerosis, gait disturbance, and bacterial or viral infections.

AUTHORS' CONCLUSIONS

Existing evidence on the safety and effectiveness of MMR/MMRV vaccines support their use for mass immunisation. Campaigns aimed at global eradication should assess epidemiological and socioeconomic situations of the countries as well as the capacity to achieve high vaccination coverage. More evidence is needed to assess whether the protective effect of MMR/MMRV could wane with time since immunisation.

Maternal Infection in Pregnancy and Childhood Leukemia: A Systematic Review and Meta-analysis

OBJECTIVE

To summarize the published evidence regarding the association between maternal infection during pregnancy and childhood leukemia.

STUDY DESIGN

In this systematic review and meta-analysis (PROSPERO number, CRD42018087289), we searched PubMed and Embase to identify relevant studies. We included human studies that reported associations of at least one measure of maternal infection during pregnancy with acute lymphoblastic leukemia (ALL) or all childhood leukemias in the offspring. One reviewer extracted the data first using a standardized form, and the second reviewer independently checked the data for accuracy. Two reviewers used the Newcastle-Ottawa Scale to assess the quality of included studies. We conducted random effects meta-analyses to pool the ORs of specific type of infection on ALL and childhood leukemia.

RESULTS

This review included 20 studies (ALL, n = 15; childhood leukemia, n = 14) reported in 32 articles. Most (>65%) included studies reported a positive association between infection variables and ALL or childhood leukemia. Among specific types of infection, we found that influenza during pregnancy was associated with higher risk of ALL (pooled OR, 3.64; 95% CI, 1.34-9.90) and childhood leukemia (pooled OR, 1.77; 95% CI, 1.01-3.11). Varicella (pooled OR, 10.19; 95% CI, 1.98-52.39) and rubella (pooled OR, 2.79; 95% CI, 1.16-6.71) infections were also associated with higher childhood leukemia risk.

CONCLUSIONS

Our findings suggest that maternal infection during pregnancy may be associated with a higher risk of childhood leukemia.

Infant milk-feeding practices and childhood leukemia: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the US Departments of Agriculture and Health and Human Services initiated a review of evidence on diet and health in these populations.

OBJECTIVES

The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding, and 4) feeding a lower versus higher intensity of human milk to mixed-fed infants with acute childhood leukemia, generally, and acute lymphoblastic leukemia, specifically.

METHODS

The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published January 1980 to March 2016, dual-screened the results using predetermined criteria, extracted data from and assessed risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

We included 24 articles from case-control or retrospective studies. Limited evidence suggests that never feeding human milk versus 1) ever feeding human milk and 2) feeding human milk for durations ≥6 mo are associated with a slightly higher risk of acute childhood leukemia, whereas evidence comparing never feeding human milk with feeding human milk for durations <6 mo is mixed. Limited evidence suggests that, among infants fed human milk, a shorter versus longer duration of human milk feeding is associated with a slightly higher risk of acute childhood leukemia. None of the included articles examined exclusive human milk feeding or the intensity of human milk fed to mixed-fed infants.

CONCLUSIONS

Feeding human milk for short durations or not at all may be associated with slightly higher acute childhood leukemia risk. The evidence could be strengthened with access to broadly generalizable prospective samples; therefore, we recommend linking surveillance systems that collect infant feeding and childhood cancer data.

Childhood vaccinations and risk of acute lymphoblastic leukaemia in children

Background

It has been proposed that childhood vaccinations protect against acute lymphoblastic leukaemia (ALL) in children by modulation of future responses to common infections in childhood. However, the available studies provide inconsistent findings, and population-based cohort studies with longitudinal information on vaccinations are lacking.

Methods

In a register-based cohort of all children born in Denmark from 1 January 1990 to 31 December 2008, followed up until age 15 years or 31 December 2009 ( n  = 1 225 404), we evaluated exposure to childhood vaccination and risk of childhood ALL, including information on ALL subtypes. Using Cox regression, we estimated hazard ratios (HRs) comparing vaccinated with unvaccinated children.

Results

Childhood ALL was diagnosed in 490 children during 10 829 194 person-years of follow-up. Neither the total number of vaccine doses received nor exposure to each vaccination given in childhood was associated with altered risk of ALL, including the following: (i) Haemophilus influenzae type b [HR, 1.04; 95% confidence interval (CI), 0.68-1.61]; ii) measles, mumps and rubella (HR, 1.01; 95% CI, 0.76-1.34); iii) whole-cell pertussis (HR, 1.10; 95% CI, 0.51-2.39); and iv) diphtheria, tetanus and inactivated polio (HR, 1.14; 95% CI, 0.42-3.13). Analyses conducted according to ALL subtypes defined by immunopheno- and karyotypes showed no association with childhood vaccination.

Conclusions

This nationwide cohort study provides no support of the proposed protective effect of childhood vaccination against childhood ALL.

Living on a farm, contact with farm animals and pets, and childhood acute lymphoblastic leukemia: pooled and meta-analyses from the Childhood Leukemia International Consortium

The associations between childhood acute lymphoblastic leukemia (ALL) and several factors related to early stimulation of the immune system, that is, farm residence and regular contacts with farm animals (livestock, poultry) or pets in early childhood, were investigated using data from 13 case-control studies participating in the Childhood Leukemia International Consortium. The sample included 7847 ALL cases and 11,667 controls aged 1-14 years. In all studies, the data were obtained from case and control parents using standardized questionnaires. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by unconditional logistic regression adjusted for age, sex, study, maternal education, and maternal age. Contact with livestock in the first year of life was inversely associated with ALL (OR = 0.65, 95% CI: 0.50, 0.85). Inverse associations were also observed for contact with dogs (OR = 0.92, 95% CI: 0.86, 0.99) and cats (OR = 0.87, 95% CI: 0.80, 0.94) in the first year of life. There was no evidence of a significant association with farm residence in the first year of life. The findings of these large pooled and meta-analyses add additional evidence to the hypothesis that regular contact with animals in early childhood is inversely associated with childhood ALL occurrence which is consistent with Greaves' delayed infection hypothesis.

Early vaccination protects against childhood leukemia: A systematic review and meta-analysis

Leukemia is the most commonly diagnosed childhood cancer, although its etiology is still largely unknown. Growing evidence supports a role for infection in the etiology of acute lymphocytic leukemia (ALL), and the involvement of the immune system suggests that vaccination may also play a role. However, the findings presented in the published literature are inconsistent. Therefore, we conducted a PRISMA systematic review and meta-analysis. 14 studies were identified and meta-analyzed. Vaccinations studied comprised Bacillus Calmette-Guérin (BCG) vaccine, Triple vaccine, Hepatitis B vaccine (HBV), Polio, Measles, Rubella, Mumps, trivalent MMR vaccine and Haemophilus influenza type B (HiB) vaccine. We observed a protective association between any vaccination in the first year of life and risk of childhood leukemia (summary odds ratio (OR) 0.58 [95% confidence interval (CI) 0.36-0.91]). When individual vaccines were analysed, some evidence of an association was seen only for BCG (summary OR 0.73 [95% CI 0.50-1.08]). In conclusion, early vaccination appears to be associated with a reduced risk of childhood leukemia. This finding may be underpinned by the association observed for BCG. Given the relatively imprecise nature of the results of this meta-analysis, our findings should be interpreted cautiously and replicated in future studies.

A systematic review and meta-analysis of the association between childhood infections and the risk of childhood acute lymphoblastic leukaemia

Background:

To determine whether childhood infections were associated with the development of childhood acute lymphoblastic leukaemia (ALL).

Methods:

We included studies that assessed any infection in childhood prior to the diagnosis of ALL in children aged 0–19 years compared to children without cancer. The primary analysis synthesised any infection against the odds of ALL, and secondary analyses assessed the frequency, severity, timing of infections, and specific infectious agents against the odds of ALL. Subgroup analyses by data source were investigated.

Results:

In our primary analysis of 12 496 children with ALL and 2 356 288 children without ALL from 38 studies, we found that any infection was not associated with ALL (odds ratio (OR)=1.10, 95% CI: 0.95–1.28). Among studies with laboratory-confirmed infections, the presence of infections increased the odds of ALL by 2.4-fold (OR=2.42, 95% CI: 1.54–3.82). Frequency, severity, and timing of infection were not associated with ALL.

Conclusions:

The hypothesis put forward by Greaves and others about an infectious aetiology are neither confirmed nor refuted and the overall evidence remains inadequate for good judgement. The qualitative difference in the subgroup effects require further study, and future research will need to address the challenges in measuring infectious exposures.

Breastfeeding, Other Early Life Exposures and Childhood Leukemia and Lymphoma

Childhood cancer incidence increases and although rare, it is a leading cause of mortality. Leukemia and lymphoma comprise 40% of all cancers in children but little is known of their etiology. In this study, we examined the associations of breastfeeding and other early life exposures with childhood leukemia and lymphoma. A population-based case-control study carried out in 2011-2013 comprised mothers of 190 incidents (2005-2013) of leukemia/lymphoma cases aged 1-19 yr at diagnosis and 384 population-based controls. Interviews based on a computerized structured questionnaire were conducted with the mothers. Multivariate logistic regression models adjusted for potential confounders assessed the association between breastfeeding patterns and childhood leukemia/lymphoma. Ever breastfeeding category was associated with a 64% decreased risk for childhood leukemia/lymphoma lsqb;odds ratio (OR) = 0.36, 95% confidence interval (CI): 0.22, 0.60lrqb; and similar trends, with a dose-response effect, were observed for any breastfeeding (exclusive and/or partial) category for 6, 12, and 18+ mo. Other infant exposures associated with cancer risk were child iron supplementation (OR = 0.39, 95% CI: 0.26, 0.59), pet ownership (OR = 0.50, 95% CI: 0.33, 0.78), paternal smoking (OR = 1.93, 95% CI: 1.18, 3.15), and having older siblings (OR = 1.18, 95% CI: 1.05, 1.33). Breastfeeding-a controllable and modifiable exposure-is inversely associated with risk for childhood leukemia and lymphoma with a dose-response effect.

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.

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.

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.

Childhood acute lymphoblastic leukemia and indicators of early immune stimulation: a Childhood Leukemia International Consortium study

The associations between childhood acute lymphoblastic leukemia (ALL) and several proxies of early stimulation of the immune system, that is, day-care center attendance, birth order, maternally reported common infections in infancy, and breastfeeding, were investigated by using data from 11 case-control studies participating in the Childhood Leukemia International Consortium (enrollment period: 1980-2010). The sample included 7,399 ALL cases and 11,181 controls aged 2-14 years. The data were collected by questionnaires administered to the parents. Pooled odds ratios and 95% confidence intervals were estimated by unconditional logistic regression adjusted for age, sex, study, maternal education, and maternal age. Day-care center attendance in the first year of life was associated with a reduced risk of ALL (odds ratio = 0.77, 95% confidence interval: 0.71, 0.84), with a marked inverse trend with earlier age at start (P < 0.0001). An inverse association was also observed with breastfeeding duration of 6 months or more (odds ratio = 0.86, 95% confidence interval: 0.79, 0.94). No significant relationship with a history of common infections in infancy was observed even though the odds ratio was less than 1 for more than 3 infections. The findings of this large pooled analysis reinforce the hypothesis that day-care center attendance in infancy and prolonged breastfeeding are associated with a decreased risk of ALL.

Childhood acute lymphoblastic leukaemia and indicators of early immune stimulation: the Estelle study (SFCE)

Background:

Factors related to early stimulation of the immune system (breastfeeding, proxies for exposure to infectious agents, normal delivery, and exposure to animals in early life) have been suggested to decrease the risk of childhood acute lymphoblastic leukaemia (ALL).

Methods:

The national registry-based case–control study, ESTELLE, was carried out in France in 2010–2011. Population controls were frequency matched with cases on age and gender. The participation rates were 93% for cases and 86% for controls. Data were obtained from structured telephone questionnaires administered to mothers. Odds ratios (OR) were estimated using unconditional regression models adjusted for age, gender, and potential confounders.

Results:

In all, 617 ALL and 1225 controls aged ⩾1 year were included. Inverse associations between ALL and early common infections (OR=0.8, 95% confidence interval (CI): 0.6, 1.0), non-first born (⩾3 vs 1; OR=0.7, 95% CI: 0.5, 1.0), attendance of a day-care centre before age 1 year (OR=0.7, 95% CI: 0.5, 1.0), breastfeeding (OR=0.8, 95% CI: 0.7, 1.0), and regular contact with pets (OR=0.8, 95% CI: 0.7, 1.0) in infancy were observed.

Conclusions:

The results support the hypothesis that conditions promoting the maturation of the immune system in infancy have a protective role with respect to ALL.

Genetic and nongenetic risk factors for childhood cancer

The causes of childhood cancer have been systematically studied for decades, but apart from high-dose radiation and prior chemotherapy there are few strong external risk factors. However, inherent risk factors including birth weight, parental age, and congenital anomalies are consistently associated with most types of pediatric cancer. Recently the contribution of common genetic variation to etiology has come into focus through genome-wide association studies. These have highlighted genes not previously implicated in childhood cancers and have suggested that common variation explains a larger proportion of childhood cancers than adult. Rare variation and nonmendelian inheritance may also contribute to childhood cancer risk but have not been widely examined.

Parental occupational paint exposure and risk of childhood leukemia in the offspring: findings from the Childhood Leukemia International Consortium

PURPOSE

It has been suggested that parental occupational paint exposure around the time of conception or pregnancy increases the risk of childhood leukemia in the offspring.

METHODS

We obtained individual level data from 13 case-control studies participating in the Childhood Leukemia International Consortium. Occupational data were harmonized to a compatible format. Meta-analyses of study-specific odds ratios (ORs) were undertaken, as well as pooled analyses of individual data using unconditional logistic regression.

RESULTS

Using individual data from fathers of 8,185 cases and 14,210 controls, the pooled OR for paternal exposure around conception and risk of acute lymphoblastic leukemia (ALL) was 0.93 [95% confidence interval (CI) 0.76, 1.14]. Analysis of data from 8,156 ALL case mothers and 14,568 control mothers produced a pooled OR of 0.81 (95% CI 0.39, 1.68) for exposure during pregnancy. For acute myeloid leukemia (AML), the pooled ORs for paternal and maternal exposure were 0.96 (95% CI 0.65, 1.41) and 1.31 (95% CI 0.38, 4.47), respectively, based on data from 1,231 case and 11,392 control fathers and 1,329 case and 12,141 control mothers. Heterogeneity among the individual studies ranged from low to modest.

CONCLUSIONS

Null findings for paternal exposure for both ALL and AML are consistent with previous reports. Despite the large sample size, results for maternal exposure to paints in pregnancy were based on small numbers of exposed. Overall, we found no evidence that parental occupational exposure to paints increases the risk of leukemia in the offspring, but further data on home exposure are needed.

Infection and childhood leukemia: review of evidence

OBJECTIVE

To analyze studies that evaluated the role of infections as well as indirect measures of exposure to infection in the risk of childhood leukemia, particularly acute lymphoblastic leukemia.

METHODS

A search in Medline, Lilacs, and SciELO scientific publication databases initially using the descriptors "childhood leukemia" and "infection" and later searching for the words "childhood leukemia" and "maternal infection or disease" or "breastfeeding" or "daycare attendance" or "vaccination" resulted in 62 publications that met the following inclusion criteria: subject aged ≤ 15 years; specific analysis of cases diagnosed with acute lymphoblastic leukemia or total leukemia; exposure assessment of mothers' or infants' to infections (or proxy of infection), and risk of leukemia.

RESULTS

Overall, 23 studies that assessed infections in children support the hypothesis that occurrence of infection during early childhood reduces the risk of leukemia, but there are disagreements within and between studies. The evaluation of exposure to infection by indirect measures showed evidence of reduced risk of leukemia associated mainly with daycare attendance. More than 50.0% of the 16 studies that assessed maternal exposure to infection observed increased risk of leukemia associated with episodes of influenza, pneumonia, chickenpox, herpes zoster, lower genital tract infection, skin disease, sexually transmitted diseases, Epstein-Barr virus, and Helicobacter pylori.

CONCLUSIONS

Although no specific infectious agent has been identified, scientific evidence suggests that exposure to infections has some effect on childhood leukemia etiology.

Investigating the relationship between mortality from respiratory diseases and childhood acute lymphoblastic leukaemia in Hungary

Our aim was to investigate the ecological association between death from infectious disease of the respiratory system and the risk of acute lymphoid leukaemia (ALL) in children aged less than 7 years. Poisson regression analyses were carried out using overall data and gender-specific models. The study included 176 cases (92(52.3 %) boys and 84 (47.7 %) girls) of ALL in those aged 0-6 years in South Hungary. Eight cases were diagnosed before the age of 1 year. A significant risk of ALL disease was observed with higher levels of mortality from the chronic respiratory diseases (p = 0.035) and pneumonia (p = 0.010) among children aged 2-5 years (Odds Ratio for trend was 1.001 and 95%CI [1.000-1.002] and Odds ratio for trend was 1.013 and 95%CI [1.003-1.023], respectively). Significantly increased risk of childhood ALL was detected among children under 1 year of age residing in areas around birth with higher levels of mortality from influenza (Odds Ratio (OR) for trend was 1.05; 95%CI [1.01-1.09]; p = 0.012). This risk was also detected in girls (p < 0.001), but not in boys (p = 0.43). Our findings provide new evidence that will help to understand the different pattern of female and male childhood ALL occurrence , but further studies are needed using detailed individual medical history to clarify the role of influenza and other infectious diseases in the etiology of childhood ALL and to explain gender-specific effects.

Exposure to infections and risk of leukemia in young children

BACKGROUND

Epidemiologic studies indicate that infections in early childhood may protect against pediatric acute lymphoblastic leukemia (ALL).

METHODS

We identified 3,402 ALL cases among children 0 to 5 years of age using the California Cancer Registry. From California birth records we randomly selected controls in a 20:1 ratio and frequency matched them to cases by birth year. We investigated markers of exposure to infections, including month of birth, timing of birth in relation to influenza and respiratory syncytial virus (RSV) seasons, and birth order based on data from California birth certificates and national infection surveillance systems.

RESULTS

We observed an increased risk of ALL for spring and summer births, and for those first exposed to an influenza or RSV season at nine to twelve months of age compared with those exposed during the first three months of life, and this association was stronger among first born children [odds ratios (OR), 1.44 and 95% confidence intervals (CI), 1.13-1.82, for influenza exposure at nine to twelve months of age]. Decreased risk was observed with increasing birth order among non-Hispanic whites but not Hispanics (OR, 0.76 and 95% CI, 0.59-096, for fourth or higher birth order among whites).

CONCLUSION

Our results support the hypothesis that infections in early childhood decrease risk of ALL.

IMPACT

Our findings implicate early life exposure to infections as protective factors for ALL in young children.

The pathophysiology of the hygiene hypothesis

There has been a considerable increase in the diagnosis of allergic diseases over the last decades. Prevalence of allergies in high-income countries and urban areas appears higher than in rural environments. While environmental factors like pollution or nutrition can be important, it is more likely that in the end they have a small association with allergies. Childhood infections and exposure to certain microbial antigens on the other hand seem to present a strong negative correlation with allergies, and therefore the increase of the allergic burden in the Western world has been frequently related to a decline of childhood infections giving birth to the "Hygiene Hypothesis". We address the issue with emphasis on the associated pathophysiology tightrope walking between the skepticism of the critics, which cast doubt on it, and the pilgrims' belief of having discovered allergy's Holy Grail.

Daycaritis

Healthy infants and toddlers who attend day care centers are at increased risk for contracting common childhood illnesses such as viral upper and lower respiratory illnesses, viral gastrointestinal infections, and acute and chronic otitis media. The author proposes that this high frequency of common infections be termed daycaritis. Daycaritis imposes significant social and economic burdens on both the family and the health care system. This review describes the most common infections seen in day care attendees, preventative measures to decrease the rates of illness, and a practical approach to diagnosis and management in the emergency department.

Early life bereavement and childhood cancer: a nationwide follow-up study in two countries

OBJECTIVE

Childhood cancer is a leading cause of child deaths in affluent countries, but little is known about its aetiology. Psychological stress has been suggested to be associated with cancer in adults; whether this is also seen in childhood cancer is largely unknown. We investigated the association between bereavement as an indicator of severe childhood stress exposure and childhood cancer, using data from Danish and Swedish national registers.

DESIGN

Population-based cohort study.

SETTING

Denmark and Sweden.

PARTICIPANTS

All live-born children born in Denmark between 1968 and 2007 (n=2 729 308) and in Sweden between 1973 and 2006 (n=3 395 166) were included in this study. Exposure was bereavement by the death of a close relative before 15 years of age. Follow-up started from birth and ended at the first of the following: date of a cancer diagnosis, death, emigration, day before their 15th birthday or end of follow-up (2007 in Denmark, 2006 in Sweden).

OUTCOME MEASURES

Rates and HRs for all childhood cancers and specific childhood cancers.

RESULTS

A total of 1 505 938 (24.5%) children experienced bereavement at some point during their childhood and 9823 were diagnosed with cancer before the age of 15 years. The exposed children had a small (10%) increased risk of childhood cancer (HR 1.10; 95% CI 1.04 to 1.17). For specific cancers, a significant association was seen only for central nervous system tumours (HR 1.14; 95% CI 1.02 to 1.28).

CONCLUSIONS

Our data suggest that psychological stress in early life is associated with a small increased risk of childhood cancer.

Hospitalisation for infection prior to diagnosis of acute lymphoblastic leukaemia in children

BACKGROUND

It has been proposed that infections in infancy and early childhood are associated with a reduced risk of childhood acute lymphoblastic leukaemia (ALL). We tested this hypothesis in a register-based study of hospitalisations for infectious diseases prior to diagnosis of childhood ALL.

PROCEDURE

A nation-wide cohort encompassing all Danish children aged 0-14 years and born between 1977 and 2008 (N = 1,778,129) was established and followed for hospitalisations for infectious diseases and risk of childhood ALL. The exposure was lagged 1 year to limit reverse causality. In the statistical analyses exposure was defined as (time dependent) number of early or late (before 2 or at/after 2 years of age) hospitalisations to further explore possible age-dependent associations.

RESULTS

A total of 815 children were diagnosed with ALL during follow-up. Risk of ALL was associated neither with hospitalisations for infectious diseases before (incidence rate ratio = 0.92, 95% confidence interval 0.78-1.07) nor at/after 2 years of age (incidence rate ratio = 1.04, 95% confidence interval 0.81-1.32). This also applied to subsets of ALL supposedly initiated prenatally.

CONCLUSION

The absence of association between hospitalisation for infections and risk of childhood ALL directs future investigations of the role of infections in development of childhood ALL towards exploration of less severe infections.

The Childhood Leukemia International Consortium

BACKGROUND

Acute leukemia is the most common cancer in children under 15 years of age; 80% are acute lymphoblastic leukemia (ALL) and 17% are acute myeloid leukemia (AML). Childhood leukemia shows further diversity based on cytogenetic and molecular characteristics, which may relate to distinct etiologies. Case-control studies conducted worldwide, particularly of ALL, have collected a wealth of data on potential risk factors and in some studies, biospecimens. There is growing evidence for the role of infectious/immunologic factors, fetal growth, and several environmental factors in the etiology of childhood ALL. The risk of childhood leukemia, like other complex diseases, is likely to be influenced both by independent and interactive effects of genes and environmental exposures. While some studies have analyzed the role of genetic variants, few have been sufficiently powered to investigate gene-environment interactions.

OBJECTIVES

The Childhood Leukemia International Consortium (CLIC) was established in 2007 to promote investigations of rarer exposures, gene-environment interactions and subtype-specific associations through the pooling of data from independent studies.

METHODS

By September 2012, CLIC included 22 studies (recruitment period: 1962-present) from 12 countries, totaling approximately 31000 cases and 50000 controls. Of these, 19 case-control studies have collected detailed epidemiologic data, and DNA samples have been collected from children and child-parent trios in 15 and 13 of these studies, respectively. Two registry-based studies and one study comprising hospital records routinely obtained at birth and/or diagnosis have limited interview data or biospecimens.

CONCLUSIONS

CLIC provides a unique opportunity to fill gaps in knowledge about the role of environmental and genetic risk factors, critical windows of exposure, the effects of gene-environment interactions and associations among specific leukemia subtypes in different ethnic groups.

Allergy and risk of childhood acute lymphoblastic leukemia: a population-based and record-based study

A deficit of normal immune stimulation in early childhood is a suspected risk factor for both childhood acute lymphoblastic leukemia (ALL) and allergies. The present study utilized a population-based case-control design using medical claims data from the National Health Insurance Research Database of Taiwan to evaluate the association between allergy and childhood leukemia. Eight hundred forty-six childhood ALL patients who were newly diagnosed during 2000 to 2008 and were older than 1 but less than 10 years of age were individually matched with 3,374 controls based on sex, birth date, and time of diagnosis (reference date for the controls). Conditional logistic regression was performed to assess the association between childhood ALL and allergies. An increased risk of ALL was observed with having an allergy less than 1 year before the case's ALL diagnosis (odds ratio (OR) = 1.7, 95% confidence interval (CI): 1.5, 2.0), more than 1 year before the case's diagnosis (OR = 1.3, 95% CI: 1.1, 1.5), and before the age of 1 year (OR = 1.4, 95% CI: 1.1, 1.7). These results suggest that the pathogenesis of childhood ALL and allergy share a common biologic mechanism.

Medically diagnosed infections and risk of childhood leukaemia: a population-based case-control study

BACKGROUND

Previous studies on the association between childhood infections and childhood leukaemia have produced inconsistent results, likely due to the recall error/bias of infection data reported by the parents. The current study used a population-based and record-based case-control design to evaluate the association between childhood leukaemia and infections using the National Health Insurance Research Database of Taiwan.

METHODS

In all, 846 childhood acute lymphoblastic leukaemia (ALL) and 193 acute myeloid leukaemia (AML) patients newly diagnosed between 2000 and 2008, aged >1 and <10 years, were included. Up to four controls (3374 for ALL and 766 for AML) individually matched to each case on sex, birth date and time of diagnosis (reference date for the controls) were identified. Conditional logistic regression was performed to assess the association between childhood leukaemia and infections.

RESULTS

Having any infection before 1 year of age was associated with an increased risk for both childhood ALL (odds ratio = 3.2, 95% confidence interval 2.2-4.7) and AML (odds ratio = 6.0, 95% confidence interval 2.0-17.8), with a stronger risk associated with more episodes of infections. Similar results were observed for infections occurring >1 year before the cases' diagnosis of childhood leukaemia.

CONCLUSIONS

Children with leukaemia may have a dysregulated immune function present at an early age, resulting in more episodes of symptomatic infections compared with healthy controls. However, confounding by other infectious measures such as birth order and day care attendance could not be ruled out. Finally, the results are only relevant to the medically diagnosed infections.

Oral health status in children with acute lymphoblastic leukemia

Leukemia is a malignancy of the bone marrow. Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy and accounts for nearly 75% of all newly diagnosed leukemias and 25% of all malignancies in childhood. The aim of the present study was to review the oral health status in children with ALL. Databases were explored using various combinations of the following keywords: "acute lymphoblastic leukemia", "children", "inflammation", "pediatric", "periodontal disease" and "periodontitis". Oral inflammatory conditions including chelitis, gingivitis, herpetic gingivostomatitis, mucositis, oral candidiasis, periodontitis and ulcerations are common manifestations in children with ALL.

RESULTS

Periodontal inflammatory conditions and oral mucositis were reported to be significantly higher in children with ALL as compared to healthy controls. Tooth morphological disorders including agenesis, microdontia, short roots and developmental defects in the enamel and dentin were more often observed in children with ALL as compared to healthy controls. Children with ALL have a reduced salivary flow rate, which makes them more susceptible to dental caries as compared to healthy children. Malocclusion due to microdontia may also trigger temporomandibular joint disorders in children with ALL; however, this relationship needs further investigations.

CONCLUSION

Oral inflammatory conditions including mucositis and gingivitis are common in children with ALL as compared to healthy children. Tooth morphological disorders including microdontia and enamel and dentin are common manifestations in children with ALL.

Incidence of childhood leukemia in Yogyakarta, Indonesia, 1998-2009

BACKGROUND

In most developing countries, incidence data for childhood cancers are less reliable, because very few population-based registries exist. The aim of this study was to present the epidemiology of childhood leukemia in the Dr. Sardjito Hospital (DSH) region, which catchment area extends beyond the boundaries of the Yogyakarta Special Province (YSP).

PROCEDURE

Health records of children, 0-14 years of age, who were diagnosed with leukemia between January 1998 and December 2009, were reviewed. Diagnosis of leukemia was confirmed by morphological and histochemical examination of marrow samples.

RESULTS

The estimated average annual incidence rate (AAIR) of childhood acute leukemia in DSH was 46.2 per million per year. Interestingly, the annual incidence rate (AIR) of childhood acute leukemia from the catchment area of DSH significantly increased from 35 in 1999 to 70 in 2009 (ANOVA, P = 0.003). The YSP population data, analyzed separately, showed an increase in AIR from 15.7 to 32.9 (ANOVA, P = 0.325) and an AAIR of 28.8. Remarkably, a relatively high frequency (25.5% in DSH and 27.7% in YSP) of children with AML was found in the group of acute leukemias.

CONCLUSION

The DSH incidence calculations may be overestimated due to an underestimation of the population number. Since the population count for YSP is more precise, the data of YSP were used for comparison with developed countries. AAIR of ALL (20.8) is relatively low compared to Western countries (22.4-37.9). The AAIR of AML (8.0) is similar to Western countries (5.0-8.0) resulting a relatively high percentage of AML versus ALL (27.7%) in YSP.

Associations between vaccination and childhood cancers in Texas regions

OBJECTIVES

To determine whether children born in Texas regions with higher vaccination coverage had reduced risk of childhood cancer.

STUDY DESIGN

The Texas Cancer Registry identified 2800 cases diagnosed from 1995 to 2006 who were (1) born in Texas and (2) diagnosed at ages 2 to 17 years. The state birth certificate data were used to identify 11 200 age- and sex-matched control subjects. A multilevel mixed-effects regression model compared vaccination rates among cases and control subjects at the public health region and county level.

RESULTS

Children born in counties with higher hepatitis B vaccine coverage had lower odds of all cancers combined (OR = 0.81, 95% CI: 0.67 to 0.98) and acute lymphoblastic leukemia (ALL) specifically (OR = 0.63, 95% CI: 0.46 to 0.88). A decreased odds for ALL also was associated at the county level with higher rates of the inactivated poliovirus vaccine (OR = 0.67, 95% CI: 0.49 to 0.92) and 4-3-1-3-3 vaccination series (OR = 0.62, 95% CI: 0.44 to 0.87). Children born in public health regions with higher coverage levels of the Haemophilus influenzae type b-conjugate vaccine had lower odds of ALL (OR: 0.58; 95% CI: 0.42 to 0.82).

CONCLUSIONS

Some common childhood vaccines appear to be protective against ALL at the population level.

Early life exposure to infections and risk of childhood acute lymphoblastic leukemia

Evidence from a growing number of studies indicates that exposure to common infections early in life may be protective against childhood acute lymphoblastic leukemia (ALL). We examined the relationship between three measures of early life exposure to infections-daycare attendance, birth order and common childhood infections in infancy-with the risk of ALL in non-Hispanic white and Hispanic children, two ethnicities that show sociodemographic differences. The analysis included 669 ALL cases (284 non-Hispanic whites and 385 Hispanics) and 977 controls (458 non-Hispanic whites and 519 Hispanics) ages 1-14 years enrolled in the Northern California Childhood Leukemia Study (NCCLS). When the three measures were evaluated separately, daycare attendance by the age of 6 months (odds ratio [OR] for each thousand child-hours of exposure = 0.90, 95% confidence interval [CI]: 0.82-1.00) and birth order (OR for having an older sibling = 0.68, 95% CI: 0.50-0.92) were associated with a reduced risk of ALL among non-Hispanic white children but not Hispanic children, whereas ear infection before age 6 months was protective in both ethnic groups. When the three measures were assessed simultaneously, the influence of daycare attendance (OR = 0.83, 95% CI: 0.73-0.94) and having an older sibling (OR = 0.59, 95% CI: 0.43-0.83) became stronger for non-Hispanic white children. In Hispanic children, a strong reduction in risk associated with ear infections persisted (OR = 0.45, 95% CI: 0.25-0.79). Evidence of a protective role for infection-related exposures early in life is supported by findings in both the non-Hispanic white and Hispanic populations within the NCCLS.

Childhood acute leukemia, early common infections, and allergy: The ESCALE Study

This study investigated the role of factors considered related to early stimulation of the immune system in the etiology of childhood acute leukemia. The national registry-based case-control study ESCALE was carried out in France in 2003-2004. Population controls were frequency matched to cases on age and gender. Data were obtained from structured telephone questionnaires administered to mothers. Odds ratios were estimated using unconditional regression models adjusted for potential confounders. Included were 634 acute lymphoblastic leukemia cases, 86 acute myeloblastic leukemia cases, and 1,494 controls aged ≥1 year. Negative associations were observed between acute lymphoblastic leukemia and birth order (P for trend < 0.0001), attendance at a day-care center before age 1 year (odds ratio (OR) = 0.8, 95% confidence interval (CI): 0.6, 1.1), prolonged breastfeeding (OR = 0.7, 95% CI: 0.5, 1.0), repeated early common infections (OR = 0.7, 95% CI: 0.6, 0.9), regular contact with farm animals (OR = 0.6, 95% CI: 0.5, 0.8), frequent farm visits in early life (OR = 0.4, 95% CI: 0.3, 0.6), and history of asthma (OR = 0.7, 95% CI: 0.4, 1.0) or eczema (OR = 0.7, 95% CI: 0.6, 0.9). Results support the hypothesis that repeated early infections and asthma may play a role against childhood acute leukemia.

Aetiology of childhood leukaemia

The acute leukaemias account for about 30% of all malignancy seen in childhood across the Western world. A peak incidence of precursor B cell ALL has emerged as socio-economic conditions have improved in countries worldwide. From twin studies and the use of neonatal blood spots it has been possible to back track the first initiating genetic events within critical haemopoietic cells to foetal development in utero for most precursor B cell ALL and some cases of AML. These events may occur as part of normal foetal development. Whether other factors (environmental or constitutional) are involved to increase the chance of these first genetic changes happening is unclear. For some leukaemias (e.g. infant MLL positive ALL) the first event appears adequate to create a malignant clone but for the majority of ALL and AML further 'genetic' changes are required, probably postnatal. Many environmental factors have been proposed as causative for leukaemia but only ionising irradiation and certain chemicals, e.g. benzene and cytotoxics (alkylators and topoisomerase II inhibitors) have been confirmed and then principally for acute myeloid leukaemia. It appears increasingly likely that delayed, dysregulated responses to 'common' infectious agents play a major part in the conversion of pre-leukaemic clones into overt precursor B cell ALL, the most common form of childhood leukaemia. Constitutional polymorphic alleleic variants in immune response genes (especially the HLA Class II proteins) and cytokines may play a role in determining the type of immune response. High penetrance germ-line mutations are involved in only about 5% of childhood leukaemias (more in AML than ALL). There is little evidence to support any role of viral transformation in causation, unlike in animals. Other environmental factors for which some evidence exists include non-ionising electromagnetic radiation and electric fields, although their mode of action in leukaemogenesis remains unclear. There is no single cause for childhood leukaemia and for most individuals a combination of factors appears to be necessary; all involving gene-environment interactions. To date few clear preventative measures have emerged, except the complete avoidance of first trimester X-rays in pregnancy; a healthy diet with adequate oral folic acid intake both preconception and early in pregnancy; and the early exposure of children to other children outside the home to facilitate stimulation and maturation of the natural immune system. Here then are clear echoes of the "hygiene hypothesis" regarding the initiation of allergies, autoimmune disease and type I diabetes mellitus in children and young people.

A meta-analysis of the association between day-care attendance and childhood acute lymphoblastic leukaemia

Background Childhood acute lymphoblastic leukaemia (ALL) may be the result of a rare response to common infection(s) acquired by personal contact with infected individuals. A meta-analysis was conducted to examine the relationship between day-care attendance and risk of childhood ALL, specifically to address whether early-life exposure to infection is protective against ALL.

Methods Searches of the PubMed database and bibliographies of publications on childhood leukaemia and infections were conducted. Observational studies of any size or location and published in English resulted in the inclusion of 14 case–control studies.

Results The combined odds ratio (OR) based on the random effects model indicated that day-care attendance is associated with a reduced risk of ALL [OR = 0.76, 95% confidence interval (CI): 0.67, 0.87]. In subgroup analyses evaluating the influence of timing of exposure, a similarly reduced effect was observed for both day-care attendance occurring early in life (≤2 years of age) (OR = 0.79, 95% CI: 0.65, 0.95) and day-care attendance with unspecified timing (anytime prior to diagnosis) (OR = 0.81, 95% CI: 0.70, 0.94). Similar findings were observed with seven studies in which common ALL were analysed separately. The reduced risk estimates persisted in sensitivity analyses that examined the sources of study heterogeneity.

Conclusions This analysis provides strong support for an association between exposure to common infections in early childhood and a reduced risk of ALL. Implications of a ‘hygiene’-related aetiology suggest that some form of prophylactic intervention in infancy may be possible.

A summary of the Agency for Healthcare Research and Quality's evidence report on breastfeeding in developed countries

OBJECTIVES

This article summarizes the Agency for Healthcare Research and Quality's evidence report on the effects of breastfeeding on term infant and maternal health outcomes in developed countries.

EVIDENCE REPORT DATA SOURCES

Medline, CINAHL, Cochrane Library, bibliographies of selected reviews, and suggestions from domain experts were surveyed. Searches were limited to English-language publications.

EVIDENCE REPORT REVIEW METHODS

Eligible comparisons examined the association between differential exposure to breastfeeding and health outcomes. We assessed 15 infant and six maternal outcomes. For four outcomes, we also updated previously published systematic reviews. For the rest of the outcomes, we either summarized previous systematic reviews or conducted new systematic reviews; randomized and non-randomized comparative trials, prospective cohorts, and case-control studies were included. Adjusted estimates were extracted from non-experimental designs. The studies were graded for methodological quality. We did not draw conclusions from poor quality studies.

EVIDENCE REPORT RESULTS

We screened over 9,000 abstracts. Thirty-two primary studies on term infant health outcomes, 43 primary studies on maternal health outcomes, and 28 systematic reviews or meta-analyses that covered approximately 400 individual studies were included in this review. A history of breastfeeding was associated with a reduction in the risk of acute otitis media, nonspecific gastroenteritis, severe lower respiratory tract infections, atopic dermatitis, asthma (young children), obesity, type 1 and 2 diabetes, childhood leukemia, and sudden infant death syndrome. There was no relationship between breastfeeding in term infants and cognitive performance. There were insufficient good quality data to address the relationship between breastfeeding and cardiovascular diseases and infant mortality. For maternal outcomes, a history of lactation was associated with a reduced risk of type 2 diabetes, breast, and ovarian cancer. Early cessation of breastfeeding or no breastfeeding was associated with an increased risk of maternal postpartum depression. There was no relationship between a history of lactation and the risk of osteoporosis. The effect of breastfeeding in mothers on return-to-prepregnancy weight was negligible, and the effect of breastfeeding on postpartum weight loss was unclear.

EVIDENCE REPORT CONCLUSIONS

A history of breastfeeding is associated with a reduced risk of many diseases in infants and mothers. Future research would benefit from clearer selection criteria, definitions of breastfeeding exposure, and adjustment for potential confounders. Matched designs such as sibling analysis may provide a method to control for hereditary and household factors that are important in certain outcomes.

Environmental factors and childhood acute leukemias and lymphomas

This review considers recent studies regarding the role of environmental factors in the etiology of childhood leukemia and lymphoma. Potential environmental risk factors identified for childhood leukemia include exposure to magnetic fields of more than 0.4 micro Tessla, exposure to pesticides, solvents, benzene and other hydrocarbons, maternal alcohol consumption (but only for certain genotypes), contaminated drinking water, infections, and high birth weight. The finding of space-time clustering and seasonal variation also supports a role for infections. There is little evidence linking childhood leukemia with lifetime exposure to ionizing radiation although fetal exposures to X-rays are associated with increased risk. Breast-feeding, consumption of fresh fruit and vegetables and having allergies all appear to be protective. Burkitt lymphoma (BL) is confined to areas of the world where malaria is endemic, with the additional involvement of the Epstein-Barr virus (EBV) as a co-factor. Environmental risk factors suggested for other types of non-Hodgkin lymphoma (NHL) include exposure to ionizing radiation (both lifetime and antenatal), pesticides, and, in utero exposure to cigarette smoke, benzene and nitrogen dioxide (via the mother). Hodgkin lymphoma (HL) is especially associated with higher levels of socioeconomic deprivation, but breast-feeding seems to confer lower risk. This is consistent with an infection or immune-response mediated etiology for HL.

How the effect of maternal age on the risk of childhood leukemia changed over time in Sweden, 1960-2004

BACKGROUND

Previous studies on the association between maternal age and risk of childhood leukemia found inconsistent results.

OBJECTIVES

We aimed to assess whether there is an association between maternal age and risk of childhood leukemia and whether such an association is modified by maternal year of birth.

METHODS

By linking nationwide Swedish registers, we analyzed leukemia incidence among all children between 1 and 5 years of age born between 1960 and 1999. We estimated incidence time trends by child year of birth (overall and stratified by maternal age) and incidence rate ratios (RRs) for maternal age groups stratified by maternal birth cohort. We tested the interaction between maternal age and child year of birth through the likelihood ratio test between nested Poisson regression models.

RESULTS

We observed 1,562 leukemia cases. The overall annual percent change (APC) was 1.00 [95% confidence interval (CI), 0.51 to 1.49]. Stratifying by maternal age classes, APCs decreased from 1.66 (0.68 to 2.65) for mothers <or= 24 years to 0.23 (-0.93 to 1.40) for mothers >or= 35 years at delivery. RRs for children born to the oldest with respect to the youngest mothers were 2.42 (1.31 to 4.67), 1.68 (1.00 to 2.72), 1.34 (0.87 to 2.01), and 0.87 (0.46-1.54) for mothers born in 1930-1934, 1940-1944, 1950-1954, and 1960-1964, respectively.

CONCLUSIONS

Childhood leukemia risk increased with maternal age for mothers born in the past, whereas maternal age had no effect on this risk for mothers born more recently. This finding may explain the inconsistency of previous studies and suggests that leukemia risk may be related to an environmental factor to which women's exposure has changed over time.

Infection and pediatric acute lymphoblastic leukemia

In this review, we provide an overview of recent findings from the Northern California Childhood Leukemia Study (NCCLS) on factors related to the immune system including child's vaccination history and measures of child's exposure to infectious agents, namely daycare attendance, infection during infancy, and parental social contact in the work place. We also provide suggestions for the next stages of studies.

Epidemiology of childhood leukemia in New Zealand: studies of infectious hypotheses

The etiology of childhood leukemia remains an enigma despite decades of research. Hypotheses of an infectious etiology have been around for a long time, and in the last 20 years there have been two main theoretical contenders. One of these involves the possibility of a specific infectious agent having a causative role, and animal leukemia viruses would be analogous to this. Another theory relates to the possible involvement of unusual patterns of infections in infancy and how they might relate to aberrant immune responses. The first of these is easier to test. In New Zealand, since the early 1990s we have embarked on a program of research on the epidemiology of childhood leukemia. One of the goals has been to test hypotheses about the role of infection in causation. A variety of study designs have been employed, including descriptive, clustering, case-control and contributions to pooled international analyses. Some of the more interesting findings include: there has been a marked increase in the incidence of acute lymphoblastic leukemia among young children in New Zealand since the mid 1960s, poorer families are at greater risk, and there is no clear support for hypotheses of an infectious cause from the New Zealand data. However because of our small total population (4 million people) we cannot produce clear results on our own. Hence our current international collaborations, for example in CLIC (the Childhood Leukemia International Consortium) represent an important step forward. As countries work together across international boundaries we have a renewed hope that the causes of the childhood leukemias will be unlocked in the foreseeable future.

Exposure to infections through day-care attendance and risk of childhood leukaemia

There is growing evidence supporting a role for infections in the aetiology of childhood leukaemia. Hypotheses proposed by both Greaves and Kinlen describe childhood leukaemia to be a rare response to one or more common infections acquired through personal contacts. Previous epidemiological studies have used day-care attendance as an indicator of the increased likelihood of early and frequent exposure to infections. It is well-documented that in developed countries, exposures to common infections occur more frequently in this type of setting. Within the Northern California Childhood Leukaemia Study, the role of social contact has been assessed and a unique 'child-hours' summary measure incorporating information on the number of months attending a day-care, mean hours per week at this day-care and the number of children in the day-care setting was constructed. In this review, the previously reported day-care results have been described, showing that in non-Hispanic White children, children in the highest category of total child-hours of exposure had a reduced risk of acute lymphoblastic leukaemia (ALL), particularly common B-cell precursor ALL (c-ALL), compared with children without such exposures, with evidence of a dose-response effect. In addition, a literature review of relevant studies has been conducted, examining the relationship between day-care attendance and risk of childhood ALL. Overall, the 14 studies identified provided consistent support for this hypothesis, with the majority of studies reporting some evidence of a reduced risk. A meta-analysis is currently underway, which will provide a quantitative evaluation of the overall consistency and strength of the association between day-care attendance or social contact and risk of childhood ALL.

Infections in early life and childhood leukaemia risk: a UK case-control study of general practitioner records

We investigated infections in early life (diagnosed in general practice) and subsequent risk of childhood leukaemia in the UK General Practice Research Database (GPRD). All children born at GPRD practices and subsequently diagnosed with leukaemia were identified as cases and were individually matched (on year of birth, sex and practice) to up to 20 controls. The final analysis included 162 leukaemia cases and 2215 matched controls. Conditional logistic regression demonstrated no evidence that children with one or more recorded infection in the first year of life had a reduced risk of leukaemia (OR=1.05, 95%CI 0.69, 1.59; P=0.83) or acute lymphoblastic leukaemia (ALL; OR=1.05, 95%CI 0.64–1.74; P=0.84). Our study provides no support for the Greaves hypothesis, which proposes that reduced or delayed exposure to infections in early life increases the risk of childhood ALL.

Childhood leukaemia and infectious exposure: a report from the United Kingdom Childhood Cancer Study (UKCCS)

Data from a national case-control study are used to explore the relationships between childhood leukaemia, infant infection and three markers of infectious exposure - birth order, infant-activity group attendance and area-based deprivation. Amongst controls, clinically diagnosed infection in the first year varied little with birth order and infant-activity group attendance - with 4 in 5 children having at least one infection, and each child averaging around 2.9 (2.8-3.0). Amongst cases of acute lymphoblastic leukaemia (ALL), the levels of infection increased as the indices of infectious exposure increased - for example, odds ratios associated with at least one infection in the first year being 0.9 (95% confidence interval (CI): 0.6-1.4) for birth order one and 1.6 (95% CI: 1.1-2.2) for birth order two or more. By contrast, interview data were misleading, with mothers - particularly case mothers - consistently under-reporting. We conclude that the findings based on clinical data, combined with the markers of infectious exposure, confirm the observation that immune dysregulation among children who develop ALL is detectable from an early age.

Vitamin and mineral supplements in pregnancy and the risk of childhood acute lymphoblastic leukaemia: a case-control study

Background

An earlier case-control study from Western Australia reported a protective effect of maternal folic acid supplementation during pregnancy on the risk of childhood acute lymphoblastic leukaemia (ALL). The present study tested that association.

Methods

A national case-control study was conducted in New Zealand. The mothers of 97 children with ALL and of 303 controls were asked about vitamin and mineral supplements taken during pregnancy.

Results

There was no association between reported folate intake during pregnancy and childhood ALL (adjusted odds ratio (OR) 1.1, 95% confidence interval (CI) 0.5–2.7). Combining our results with the study from Western Australia and another study from Québec in a meta-analysis gave a summary OR of 0.9 (95% CI 0.8–1.1).

Conclusion

Our own study, of similar size to the Australian study, does not support the hypothesis of a protective effect of folate on childhood ALL. Neither do the findings of the meta-analysis.