Day-care, early common infections and childhood acute leukaemia: a multicentre French case-control study

Childcare attendance and risk of childhood acute lymphoblastic leukaemia: A register study based on the Danish childcare database

Childhood acute lymphoblastic leukaemia (ALL) is suggested to result from a dysregulated immune response to infections in children with a preleukaemic state. Childcare in early life supposedly may protect against childhood ALL by facilitating sufficient exposure to infections to stimulate and ensure normal maturation of the immune system. We assessed the association between childcare attendance before age 2 years and risk of childhood ALL in a register-based cohort study, including all children aged 2 to 14 years born in Denmark during 1991 to 2014 with available childcare information recorded in the Danish Childcare Database (n = 1 116 185). Cox regression was used to estimate hazard ratios (HRs) comparing children enrolled in childcare and children not enrolled before age 2 years. Further, we assessed the association according to age at enrolment, type of childcare facility and specific ALL subtypes. During 10 460 811 person-years of follow-up, 460 children developed ALL at ages 2 to 14 years. Of these, 57 (12.4%) never attended childcare before age 2 years compared with 10.6% in the total cohort. Compared with homecare, childcare attendance before age 2 years was associated with a statistically non-significantly, marginally decreased risk of childhood ALL with adjusted HR = 0.87 (95% confidence interval [CI]: 0.65-1.16). Risk estimates did neither vary statistically significantly by age at enrolment nor by type of childcare facility and also not between childhood ALL subtypes, including frequently prenatally initiated ALL subtypes. Results from this large, nationwide register-based study provided no evidence that childcare attendance in the first years of life protects against childhood ALL.

Association between maternal breastfeeding and risk of systemic neoplasms of offspring

Background

Breastfeeding might prevent childhood cancer by stimulating the immune system.

Methods

The following databases, including PubMed, Embase, and Cochrane Library, were searched from inception to January 10, 2021.

Results

In dose-dependent manner, there was a statistically significant inverse association between any breastfeeding and the incidence of childhood cancer. There was no evidence that breastfeeding was inversely related to childhood cancer of the skeletal, reproductive, or sensory systems. However, breastfeeding was inversely associated with the incidence of hematological malignancies and cancers of the nervous and urinary systems. Among hematological malignancies, the relationship was significant for acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML), but not for acute non-lymphocytic leukemia (ANLL), Hodgkin’s lymphoma (HL), or non-HL.

Conclusions

The evidences demonstrated that breastfeeding have a potential protective role in preventing selective childhood cancer growth, especially for ALL, AML, cancer of nervous and urinary systems. This study recommended that breastfeeding be extended for as long as possible or maintained for at least 6 months to prevent selective childhood cancer growth.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13052-022-01292-9.

Infections and the development of childhood acute lymphoblastic leukemia: a population-based study

An infectious trigger for childhood acute lymphoblastic leukemia is hypothesized and we assessed the association between the rate, type, and critical exposure period for infections and the development of acute lymphoblastic leukemia. We conducted a matched case-control study using administrative databases to evaluate the association between the rate of infections and childhood acute lymphoblastic leukemia diagnosed between the ages of 2-14 years from Ontario, Canada and we used a validated approach to measure infections. In 1600 cases of acute lymphoblastic leukemia, and 16 000 matched cancer-free controls aged 2-14 years, having >2 infections/year increased the odds of childhood acute lymphoblastic leukemia by 43% (odds ratio = 1.43, 95% confidence interval 1.13-1.81) compared to children with ≤0.25 infections/year. Having >2 respiratory infections/year increased odds of acute lymphoblastic leukemia by 28% (odds ratio =1.28, 95% confidence interval 1.05-1.57) compared to children with ≤0.25 respiratory infections/year. Having an invasive infection increased the odds of acute lymphoblastic leukemia by 72% (odds ratio =1.72, 95% confidence interval 1.31-2.26). Having an infection between the age of 1-1.5 years increased the odds of acute lymphoblastic leukemia by 20% (odds ratio = 1.20, 95% confidence interval 1.04-1.39). Having more infections increased the odds of developing childhood acute lymphoblastic leukemia and having an infection between the ages of 1-1.5 years increased the odds of childhood acute lymphoblastic leukemia.

Diet as a Potential Moderator for Genome Stability and Immune Response in Pediatric Leukemia

Simple Summary

Pediatric acute lymphoblastic leukemia (ALL) is the most prevalent cancer affecting children in developed societies. Here, we review the role of diet in control of the incidence and progression of childhood ALL. Prenatally, ALL risk is associated with higher birthweights of newborns, suggesting that ALL begins to evolve in-utero. Indeed, maternal diet influences the fetal genome and immune development. Postnatally, breastfeeding associates with decreased risk of ALL development. Finally, for the ALL-affected child, certain dietary regimens that impact the hormonal environment may impede disease progression. Improved understanding of the dietary regulation of hormones and immunity may inform better approaches to predict, protect, and ultimately save children afflicted with pediatric leukemia.

Abstract

Pediatric leukemias are the most prevalent cancers affecting children in developed societies, with childhood acute lymphoblastic leukemia (ALL) being the most common subtype. As diet is a likely modulator of many diseases, this review focuses on the potential for diet to influence the incidence and progression of childhood ALL. In particular, the potential effect of diets on genome stability and immunity during the prenatal and postnatal stages of early childhood development are discussed. Maternal diet plays an integral role in shaping the bodily composition of the newborn, and thus may influence fetal genome stability and immune system development. Indeed, higher birth weights of newborns are associated with increased risk of ALL, which suggests in-utero biology may shape the evolution of preleukemic clones. Postnatally, the ingestion of maternal breastmilk both nourishes the infant, and provides essential components that strengthen and educate the developing immune system. Consistently, breast-feeding associates with decreased risk of ALL development. For children already suffering from ALL, certain dietary regimens have been proposed. These regimens, which have been validated in both animals and humans, alter the internal hormonal environment. Thus, hormonal regulation by diet may shape childhood metabolism and immunity in a manner that is detrimental to the evolution or expansion of preleukemic and leukemic ALL clones.

DNA methylation and the hygiene hypothesis: connecting respiratory allergy and childhood acute lymphoblastic leukemia

Aim: The hygiene hypothesis states that a lack of infection in early-life suppresses immune system development, and is linked to respiratory allergy (RA) and childhood acute lymphoblastic leukemia (ALL) risk. Little is known about underlying mechanisms, but DNA methylation is altered in RA and ALL, and in response to infection. We investigated if aberrant methylation may be in common between these diseases and associated with infection. Materials & methods: RA and ALL disease-associated methylation signatures were compared and related to exposure-to-infection signatures. Results: A significant number of genes overlapped between RA and ALL signatures (p = 0.0019). Significant overlaps were observed between exposure-to-infection signatures and disease-associated signatures. Conclusion: DNA methylation may be a mediating mechanism through which the hygiene hypothesis is associated with RA and ALL risk.

DNA damage signalling from the placenta to foetal blood as a potential mechanism for childhood leukaemia initiation

For many diseases with a foetal origin, the cause for the disease initiation remains unknown. Common childhood acute leukaemia is thought to be caused by two hits, the first in utero and the second in childhood in response to infection. The mechanism for the initial DNA damaging event are unknown. Here we have used in vitro, ex vivo and in vivo models to show that a placental barrier will respond to agents that are suspected of initiating childhood leukaemia by releasing factors that cause DNA damage in cord blood and bone marrow cells, including stem cells. We show that DNA damage caused by in utero exposure can reappear postnatally after an immune challenge. Furthermore, both foetal and postnatal DNA damage are prevented by prenatal exposure of the placenta to a mitochondrially-targeted antioxidant. We conclude that the placenta might contribute to the first hit towards leukaemia initiation by bystander-like signalling to foetal haematopoietic cells.

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.

The association between birth order and childhood brain tumors: a systematic review and meta-analysis

The incidence of childhood brain tumors (CBT) has increased worldwide, likely resulting from the improvements of early diagnostics. We conducted a systematic review and meta-analysis to clarify the association between birth order and CBT. We followed established guidelines to systematically search Ovid Medline, PubMed, and the Cochrane Library for English language studies, published before March 2018. Quality assessment was performed using the Newcastle-Ottawa Scale. Meta-analysis provided pooled risk estimates and their 95% confidence intervals (CIs) for birth order and CBT. We identified 16 case-control studies with a total sample of 32 439 cases and 166 144 controls and three prospective cohort studies (i.e. 4515 incident cases of CBTs among 5 281 558 participants). Compared with first birth order, the meta-odds ratio for second birth order in case-control studies was 1.04 (95% CI: 1.01-1.07), that for third birth order was 0.98 (95% CI: 0.90-1.06), and that for fourth order was 0.85 (95% CI: 0.78-0.92). The meta-hazard ratio for second or higher birth order compared with first birth order in cohort studies was 1.00 (95% CI: 0.96-1.05). We found no association between birth order and CBT in both case-control and cohort study designs; the small association observed for fourth birth order deserves further consideration.

The emerging story of acute lymphoblastic leukemia among the Latin American population - biological and clinical implications

Higher incidence rates and poor outcomes have been reported among Latin American patients (Latinos) with acute lymphoblastic leukemia (ALL). Distinct patterns in recent genomic studies allude to a predisposing genetic component. In this review, we critically examine the increasing amount of empirical information on the epidemiology, outcomes and genomics of Latinos with ALL. We discuss the immense diversity within the Latino community and varying definitions of what is considered Latino, which pose an epidemiological challenge. Environmental factors have been evaluated as possible predisposing factors in the development of ALL but studies have produced conflicting results. In this review we describe chromosomal abnormalities and the specific genomic landscape in Latinos with ALL and their association with unfavorable prognosis, focusing on the higher frequency of Philadelphia chromosome-Like ALL. Recent data suggest an association between polymorphisms that are commonly found in indigenous Americans and high rates of ALL. The review compares the distribution of ALL throughout the various countries in Latin America in an attempt to shed some epidemiological light on the genetic ancestry of ALL. We additionally identify areas where research is warranted in efforts toward the advent of novel targeted agents that are relevant in improving outcomes within the Latino community.

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.

IFN-γ directly inhibits murine B-cell precursor leukemia-initiating cell proliferation early in life

The early-life immune environment has been implicated as a modulator of acute lymphoblastic leukemia (ALL) development in children, with infection being associated with significant changes in ALL risk. Furthermore, polymorphisms in several cytokine genes, including IL-10 and IFN-γ, are associated with leukemia development. However, the mechanisms and timing of these influences remain unknown. Here, we use the Eμ-ret transgenic mouse model of B-cell precursor ALL to assess the influence of IFN-γ on the early-life burden of leukemia-initiating cells. The absence of IFN-γ activity resulted in greater numbers of leukemia-initiating cells early in life and was associated with accelerated leukemia onset. The leukemia-initiating cells from IFN-γ-knockout mice had reduced suppressor of cytokine signaling (SOCS-1) expression, were significantly more sensitive to IFN-γ, and exhibited more rapid expansion in vivo than their wild-type counterparts. However, sensitivity to this inhibitory pathway was lost in fully transformed IFN-γ-knockout leukemia cells. These results demonstrate that the influence of IFN-γ on ALL progression may not be mediated by selection of nascent transformed cells but rather through a general SOCS-mediated reduction in B-cell precursor proliferation. Thus, while cytokine levels may influence leukemia at multiple points during disease progression, our study indicates a significant early influence of basal, infection-independent cytokine production on leukemogenesis.

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.

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.

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.

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.

A nationwide population-based cohort study on tonsillectomy and subsequent cancer incidence

OBJECTIVES/HYPOTHESIS

Tonsillectomy is related to increased risk of certain types of cancer. This study evaluates the possible association between tonsillectomy and cancer in Taiwan.

METHODS

Data from the National Health Insurance system of Taiwan was used. A cohort study consisting of 997 patients with a new diagnosis of tonsillectomy from 2000 to 2005 and a comparison cohort of 3,988 subjects without tonsillectomy were used in the Poisson regression analysis to estimate the incidence rate ratios (IRRs) and 95% confidence intervals (CIs) of cancers.

RESULTS

The incidence rate of all cancer types was higher in the tonsillectomy group than in the control group (4.28 vs. 2.97 per 1,000 person-years, respectively), with an IRR = 1.54 and 95% CI of 1.05 to 2.25, but the significant difference was limited to patients with more than 3 years follow-up. Site-specific analysis found no significant association between tonsillectomy and any individual cancer after adjusting for age, sex, hyperlipidemia, hypertension, and diabetes; however, tonsillectomy patients with more than 3 years follow-up had a marginally significantly higher risk for breast cancer development (adjusted IRR = 2.62; CI = 0.97-7.03).

CONCLUSION

Our study found that Taiwanese people with tonsillectomy have a significantly higher overall risk of developing cancer and a marginally higher risk of developing breast cancer when follow-up is longer than 3 years.

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.

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.

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.

The association between acute lymphoblastic leukemia in children and Helicobacter pylori as the marker for sanitation

Background

Greaves “delayed infection” hypothesis suggested that Acute Lymphoblastic Leukemia (ALL) in children is caused by a lack of exposure to infection in infancy, which may be due higher standards of sanitation. We have conducted an ecologic analysis of the relationship between sanitation, using Helicobacter pylori (H. pylori) as the marker, and the incidence of childhood ALL in 127 cancer registries from 28 countries.

Results

There were inverse associations between H. pylori prevalence and ALL incidence rates in children. These associations were minor and only significant for ALL incidence rates for all cancer registries. They became non-significant and smaller in magnitude when the population source and/or the GNP per capita were added to the relationship. Furthermore, these results were unchanged when the associations were examined using the Generalized Estimating Equations.

Conclusions

Although the findings showed lower prevalence of H. pylori and improved sanitation is associated with increased incidence of childhood ALL, they do not conclusively support Greaves “delayed infection” hypothesis.

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.

Profound deficit of IL10 at birth in children who develop childhood acute lymphoblastic leukemia

BACKGROUND

Childhood acute lymphoblastic leukemia (ALL) may originate via abnormal immune responses to infectious agents. It is unknown whether prenatal immune development may differ in children who develop the disease. The current study examines the association between neonatal cytokine profiles, a proxy measure for a child's prenatal immune development, and childhood ALL.

METHODS

Neonatal blood spots of 116 childhood ALL cases and 116 controls living in California were ascertained. Eleven cytokines associated with Th1, Th2, and Th17 lymphocytes were measured using a multiplex bead-based assay. Unconditional logistic regression was done to estimate the odds ratio (OR) by measuring the association between neonatal cytokines and ALL adjusted for age, sex, race/ethnicity, and household income.

RESULTS

Of the 11 cytokines measured, 5 [interleukin (IL)4, IL6, IL10, IL12, and IL13] were detectable. Except for IL12, the other 4 cytokines were all significantly lower among cases than controls. In a multivariable model including the 5 cytokines, only IL10 remained independently associated with childhood ALL with an OR = 0.04, 95% CI: 0.01 to 0.18, comparing the highest tertile to the lowest tertile.

CONCLUSIONS

A child's neonatal level of IL10, a key regulator for modulating the intensity and duration of immune responses, is associated with his/her subsequent risk of developing ALL.

IMPACT

The current analysis shows that children with ALL may have a dysregulated immune function present at birth.

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.

Birth order and risk of childhood cancer: a pooled analysis from five US States

The causes of childhood cancers are largely unknown. Birth order has been used as a proxy for prenatal and postnatal exposures, such as frequency of infections and in utero hormone exposures. We investigated the association between birth order and childhood cancers in a pooled case-control dataset. The subjects were drawn from population-based registries of cancers and births in California, Minnesota, New York, Texas and Washington. We included 17,672 cases <15 years of age who were diagnosed from 1980 to 2004 and 57,966 randomly selected controls born 1970-2004, excluding children with Down syndrome. We calculated odds ratios and 95% confidence intervals using logistic regression, adjusted for sex, birth year, maternal race, maternal age, multiple birth, gestational age and birth weight. Overall, we found an inverse relationship between childhood cancer risk and birth order. For children in the fourth or higher birth order category compared to first-born children, the adjusted OR was 0.87 (95% CI: 0.81, 0.93) for all cancers combined. When we examined risks by cancer type, a decreasing risk with increasing birth order was seen in the central nervous system tumors, neuroblastoma, bilateral retinoblastoma, Wilms tumor and rhabdomyosarcoma. We observed increased risks with increasing birth order for acute myeloid leukemia but a slight decrease in risk for acute lymphoid leukemia. These risk estimates were based on a very large sample size, which allowed us to examine rare cancer types with greater statistical power than in most previous studies, however the biologic mechanisms remain to be elucidated.

Wilms' tumour: a systematic review of risk factors and meta-analysis

Wilms' tumour comprises 95% of all renal cancers among children less than 15 years of age. The purpose of this review is to examine the existing literature on perinatal and environmental risk factors for Wilms' tumour. A search for epidemiological studies that examined risk factors for Wilms' tumour was undertaken in Medline, LILACS, ISI Web of Science and Dissertation Abstracts. A total of 37 studies, including 14 cohort, 21 case-control and 2 case-cohort studies, were identified that examined environmental and perinatal risk factors. Most studies were from Western Europe and North America, and among case-control studies, 16 used randomly selected population-based controls. We observed a significantly increased risk of Wilms' tumour with maternal exposure to pesticides prior to the child's birth (OR = 1.37 [95% CI 1.09, 1.73]), high birthweight (OR = 1.36 [95% CI 1.12, 1.64]) and preterm birth (OR = 1.44 [95% CI 1.14, 1.81]), although the results regarding pesticide exposure may be subject to publication bias (Egger's test, P = 0.09). Further analyses to adjust for the heterogeneity in the results for high birthweight and preterm birth did not statistically change the significance of the results. Additionally, an increased though not statistically significant risk of Wilms' tumour was associated with maternal hypertension (OR = 1.30 [95% CI 0.99, 1.72]), and, compared with the first born, being a second or later birth was associated with a significantly decreased risk (OR = 0.82 [95% CI 0.71, 0.95]). This review suggests a role for several perinatal and environmental risk factors in the aetiology of Wilms' tumour.

Genetic polymorphisms in adaptive immunity genes and childhood acute lymphoblastic leukemia

BACKGROUND

Childhood acute lymphoblastic leukemia (ALL) has been hypothesized to have an infection- and immune-related etiology. The lack of immune priming in early childhood may result in abnormal immune responses to infections later in life and increase ALL risk.

METHODS

The current analyses examined the association between childhood ALL and 208 single-nucleotide polymorphisms (SNP) of 29 adaptive immune function genes among 377 ALL cases and 448 healthy controls. Single SNPs were analyzed with a log-additive approach using logistic regression models adjusted for sex, age, Hispanic ethnicity, and race. Sliding window haplotype analyses were done with haplotypes consisting of 2 to 6 SNPs.

RESULTS

Of the 208 SNPs, only rs583911 of IL12A, which encodes a critical modulator of T-cell development, remained significant after accounting for multiple testing (odds ratio for each copy of the variant G allele, 1.52; 95% confidence interval, 1.25-1.85; P = 2.9 x 10(-5)). This increased risk was stronger among firstborn children of all ethnicities and among non-Hispanic children with less day care attendance, consistent with the hypothesis about the role of early immune modulation in the development of childhood ALL. Haplotype analyses identified additional regions of CD28, FCGR2, GATA3, IL2RA, STAT4, and STAT6 associated with childhood ALL.

CONCLUSION

Polymorphisms of genes on the adaptive immunity pathway are associated with childhood ALL risk.

IMPACT

Results of this study support an immune-related etiology of childhood ALL. Further confirmation is required to detect functional variants in the significant genomic regions identified in this study, in particular for IL12A.

Selection bias in case-control studies on household exposure to pesticides and childhood acute leukemia

The goal of this study was to investigate the potential for selection bias in published case-control studies on household exposure to pesticides and childhood acute leukemia; most studies have reported positive findings. Items to evaluate the potential for selection bias were first developed. They focused on the source populations that gave rise to cases and controls, the probabilistic selection of subjects from the source, and the losses of the subjects actually selected. A quantitative assessment of bias was also carried out. Potential sources of selection bias were found in all the studies, but none of them were observed across all the studies. Main sources of potential bias were a non-concurrent selection of controls with respect to cases, the use of control diagnoses possibly caused by pesticide exposure in hospital-based studies, and non-participation of selected eligible subjects. A quantitative assessment of bias concluded that non-participation alone could not explain the reported positive associations. We conclude that overall, selection bias, as a likely source of bias in these studies, does not seem to explain their positive findings. Our analysis provides arguments strengthening the conclusions on associations reported in earlier studies.

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.

Toward general prophylactic cancer vaccination

It is well established that chronic infections can lead to cancer. Almost unknown is that, in contrast, acute brief viral and bacterial infections may have beneficial effects in cases of established neoplastic disease, while exposure to pathogenic products by infection, vaccination, and inhalation can cause prophylactic effects. In the following I will align evidence from case studies of spontaneous regression and from epidemiological studies with recent immunology to conclude that pathogenic substances belonging to the group of "pathogen-associated molecular patterns" can trigger the innate immune system to establish anti-neoplastic immune responses. A better understanding of the protective role of the innate immune system might leverage considerable prophylactic potential.

Maternal immunoglobulin E and childhood leukemia

Childhood leukemia, particularly acute lymphoblastic leukemia (ALL), has long been hypothesized to be affected by abnormal immune responses to microbial challenges stemming from a lack of immune modulation in early childhood. Studies of allergies suggest that a child's immune development may be modulated by maternal immune status. We conducted a study to explore the relationship between maternal immunoglobulin E (IgE) and childhood leukemia and to investigate whether maternal immune status can influence childhood leukemia risk. Serum total and specific IgE (respiratory and food) were measured in biological mothers of 352 children (193 healthy controls and 159 leukemia cases, including 139 ALL cases) ages <8 years who were enrolled in the Northern California Childhood Leukemia Study. Odds ratios associated with maternal IgE were calculated using unconditional logistic regression adjusted for child's age, sex, race/ethnicity, and annual household income. A positive association between childhood leukemia or ALL and elevated levels of maternal serum total IgE was observed, especially among Hispanics. In addition, a positive association was observed between childhood leukemia or ALL and maternal respiratory or food IgE status. These results suggest that maternal immune function may play a crucial role in the etiology of childhood leukemia, although additional studies need to be conducted to confirm the results of this study and provide a perspective on mechanisms.

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.

Immunotherapy for malignant melanoma--tracing Ariadne's thread through the labyrinth

A working group (FEBIM) within the European Organisation for Research and Treatment of Cancer undertook extensive studies on the possible association of infectious diseases and the risk of malignant melanoma. These studies provided evidence that several infectious diseases and also some vaccines including the anti-tuberculosis vaccine, BCG, derived from Mycobacterium bovis, confer a significant level of protection against this form of cancer. In recent years, the importance of immunoregulatory networks in the establishment of tolerance to tumour antigens and the key role of the innate immune system in the development of such networks have been recognised. The molecular patterns of micro-organisms activate pattern recognition receptors on antigen presenting cells and determine the qualitative nature of the ensuing immune response. Bacteria in the actinomycetales family, notably members of the genus Mycobacterium, exhibit particularly powerful adjuvant activity and profoundly affect underlying patterns of immune reactivity. In particular, there is growing evidence that a heat-killed preparation of a strain of Mycobacterium vaccae is able to down-regulate patterns of immune reactivity that favour the tumour and to induce those that lead to anti-cancer immune responses. The results of preliminary clinical observations with melanoma patients, and published studies on other cancers, point to the need for more formal clinical trials.

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.

Allergies and childhood leukemia

A majority of studies to date have reported an inversed association between allergies and childhood leukemia. However, this association is likely an indirect one and may represent some shared underlying immune mechanisms that have been explained in the context of the "hygiene hypothesis", which has been thought to play an important role in the development of both allergies and childhood leukemia. This review focuses on what we know so far about the role of various immune cells (Th1, Th2, T regulatory and Th17 cells) in the development of allergies and how they may potentially be related to the etiology of childhood leukemia. In addition, the utilities of genetic and molecular studies to disentangle the association between allergies and childhood leukemia and to elucidate the biological mechanisms are also discussed.

Long-term use of medications and destructive periodontal disease

BACKGROUND

Knowledge of typical medication use among patients with chronic periodontitis or destructive periodontal disease is limited. The aim of this study was to associate periodontitis severity with the use of different classes of medications.

METHODS

Patients (N=12,631) who had medical, dental, and pharmaceutical coverage with a health maintenance organization and whose severity of destructive periodontal disease was diagnosed by a dentist or specialist were included in the study. The rate of drug use over 7 years was related to the severity of destructive periodontal disease by means of Poisson regression models.

RESULTS

Individuals with moderate to advanced periodontitis had significantly lower fill rates for the respiratory agents (antihistamines: -23%, 95% confidence interval [CI]: -10% to -34%; decongestants: -24%, 95% CI: -13% to -34%; and cough/cold medications: -12%, 95% CI: -3% to -21%) and anti-infective agents (antibiotics: -12%, 95% confidence interval: -6% to -18%; urinary anti-infectives: -36%, 95% CI: -6% to -56%; and topical antibiotics: -18%, 95% CI: -5% to -29%).

CONCLUSIONS

More severe periodontitis was a marker for reduced medication use for allergies and infections. The associations between destructive periodontal disease, infections, allergies, and the hygiene hypothesis need further exploration.

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.