The risk profile of childhood leukaemia in Greece: a nationwide case-control study

Vaccination and the risk of childhood acute leukaemia: the ESCALE study (SFCE)

BACKGROUND

In 2002, a poster alerted the French health authorities to the possibility that the risk of childhood leukaemia might be increased by hepatitis B vaccination. Elucidating the role of vaccination in the aetiology of childhood acute leukaemia (AL) was therefore included in the objectives of an ongoing national study.

METHODS

The ESCALE study was a French national population-based case-control study conducted in France in 2003 and 2004 in order to investigate the role of infectious, environmental and genetic factors in four childhood neoplastic diseases (leukaemia, lymphoma, neuroblastoma and brain tumour). The controls were randomly selected from the French population and age and gender frequency matched with the cases. A total of 776 cases of AL (91% of the eligible cases) and 1681 controls (71% of the eligible controls) were included. In a specific standardized telephone interview, which was the same for both the cases and controls, each mother was asked to read out her child's complete vaccination record.

RESULTS

No association between vaccination and the risk of childhood AL: acute lymphoblastic leukaemia or acute myeloblastic leukaemia was observed. No relationship between the risk of leukaemia and the type of vaccine, number of doses of each vaccine, total number of injections, total number of vaccine doses or number of early vaccinations was evidenced. No confounding factor was observed.

CONCLUSION

The study did not show any evidence of a role of vaccination in the aetiology of childhood leukaemia.

Parental alcohol consumption and childhood cancers: a review

The etiology of childhood cancers remains generally unknown. Given that the metabolites of alcohol are likely carcinogens and that leukemia, the most frequent childhood cancer, can arise in utero, the study of alcohol consumption as a potential risk factor for the development of childhood cancer is justified. This article summarizes the epidemiological evidence on the association between parental exposure to alcohol and the risk of childhood cancers. To do this, a thorough search of the literature from 1960 to 2003 using the PubMed database was carried out. It yielded 33 case-control studies published between 1982 and 2003, including 13 studies that considered paternal exposure in the preconceptional period. In 10 of the 33 studies at least 1 statistically significant risk increase was reported in relation with parental alcohol consumption; in 7 of these studies the increase was related to maternal consumption, whereas in 3 studies, it was related to paternal consumption. The cancers most often found associated with parental drinking were leukemia, brain tumors, and neuroblastoma. A few studies also reported a protective effect with maternal exposure at modest levels. Inconsistencies in the results and the low risks reported do not suggest an association between childhood cancer and parental consumption of alcohol. However, before reaching any definitive conclusions, methodological issues need to be addressed in future studies, as well as the role of genetic susceptibility. Moreover, subtypes of specific cancers need to be studied separately.

Maternal hemoglobin concentration during pregnancy and risk of infant leukaemia: a children's oncology group study

In contrast to the positive association found in three studies between maternal anaemia during pregnancy and childhood leukaemia, no such association was found in infant leukaemia (odds ratio 0.85, 95% confidence interval 0.53–1.37).

Birth weight, maternal weight and childhood leukaemia

There is mounting evidence that childhood leukaemia is associated with high birth weight, but few studies have examined the relationship between leukaemia and other perinatal factors that influence birth weight, such as maternal weight or gestational weight gain. This case-cohort study included 916 acute lymphocytic leukaemia (ALL) and 154 acute myeloid leukaemia (AML) cases diagnosed prior to age 10 years between 1985 and 2001 and born in New York State excluding New York City between 1978 and 2001. Controls (n=9686) were selected from the birth cohorts for the same years. Moderate increased risk of both ALL and AML was associated with birth weight 3500 g or more. For ALL, however, there was evidence of effect modification with birth weight and maternal prepregnancy weight. High birth weight was associated with ALL only when the mother was not overweight while heavier maternal weight was associated with ALL only when the infant was not high birth weight. Increased pregnancy-related weight gain was associated with ALL. For AML, birth weight under 3000 g and higher prepregnancy weight were both associated with increased risk. These findings suggest childhood leukaemia may be related to factors influencing abnormal fetal growth patterns.

Maternal and birth characteristics in relation to childhood leukaemia

Our objective was to investigate the association of childhood leukaemia with selected maternal and birth characteristics by conducting a population-based case-control study using linked cancer registry and birth certificate records for Washington State. We compared maternal and infant characteristics of 595 Washington-born residents <20 years old with leukaemia diagnosed during 1981-2003, and 5,950 control children, using stratified analysis and logistic regression. Maternal age 35+ years (odds ratio [OR] 1.5; 95% confidence interval [CI] 1.1, 2.0), infant birthweight 4,000+ g (OR 1.4; 95% CI 1.1, 1.8), neonatal jaundice (OR 1.5; 95% CI 1.1, 2.1), and Down's syndrome (OR 31.3; 95% CI 6.4, 153.4) were associated with an increased risk of leukaemia. Among women with 2+ pregnancies, having at least two prior early (<20 weeks' gestation) fetal deaths was also associated with an increased risk (OR 1.5; 95% CI 0.97, 2.1). Maternal unmarried status (OR 0.7; 95% CI 0.6, 0.9) and African American race (OR 0.5; 95% CI 0.3, 0.9) were associated with a decreased risk. These results were more marked for acute lymphocytic leukaemia (ALL) than for acute myeloid leukaemia (AML), and for leukaemia diagnosed <5 years of age. These results may provide clues to the aetiology of childhood leukaemia. Genetic epidemiological studies are needed to expand our knowledge of inherent and possibly prenatal influences on the occurrence of this disease.

Parental smoking and the risk of childhood leukemia

Cigarette smoke has been linked to adult myeloid leukemia; however, the association between parental smoking and childhood leukemia remains unclear. Parental smoking and the risk of childhood leukemia were examined in the Northern California Childhood Leukemia Study, a case-control study, between 1995 and 2002. The present analysis included 327 acute childhood leukemia cases (281 acute lymphoblastic leukemia (ALL) and 46 acute myeloid leukemia (AML)) and 416 controls matched on age, sex, maternal race, and Hispanic ethnicity. Maternal smoking was not associated with an increased risk of either ALL or AML. Paternal preconception smoking was significantly associated with an increased risk of AML (odds ratio = 3.84, 95% confidence interval: 1.04, 14.17); an increased risk for ALL was suggestive for paternal preconception smoking (odds ratio = 1.32, 95% confidence interval: 0.86, 2.04). Greater risks of ALL were observed compared with the risk associated with paternal preconception smoking alone, when paternal preconception smoking was combined with maternal postnatal smoking (p(interaction) = 0.004) or postnatal passive smoking exposure (p(interaction) = 0.004). These results strongly suggest that exposure to paternal preconception smoking alone or in combination with postnatal passive smoking may be important in the risk of childhood leukemia.

An overview of the association between allergy and cancer

Numerous epidemiological studies have evaluated some aspect of the association between a history of allergy and cancer occurrence. In this article, an overview of the epidemiological evidence is presented with a discussion of a number of methodological issues important in this area of study. Literature searches were conducted using the MEDLINE database from 1966 through to August 2005 to identify articles that explored a personal history of allergic disorders as a risk factor for cancer. Although it is difficult to draw conclusions between allergy and cancer at many sites because of insufficient evidence or a lack of consistency both within and among studies completed to date, strong inverse associations have been reported for pancreatic cancer and glioma, whereas lung cancer was positively associated with asthma. Additional studies are needed to confirm these finding and to address the limitations of previous studies, including the validity and reliability of exposure measures and control for confounding. Further, large prospective studies using cancer incidence would be particularly useful, including studies using biological markers of allergic status to reduce potential misclassification and to confirm the results of previous studies based on self-report. There is also a need for further basic research to clarify a potential mechanism, should an association exist.

Maternal coffee and alcohol consumption during pregnancy, parental smoking and risk of childhood acute leukaemia

INTRODUCTION

We investigated the role of maternal alcohol and coffee drinking and parental smoking on the risk of childhood acute leukemia in a multicenter case-control study.

METHODS

The study included 280 incident cases and 288 hospitalized controls, frequency matched with the cases by age, gender and center. Data collection was completed by face-to-face standardized interviews of the case and control mothers.

RESULTS

An association with maternal alcohol consumption during pregnancy was observed with acute lymphoid leukemia (ALL) (OR=2.0 [1.4-3.0]) and acute non-lymphoid leukemia (ANLL) (OR=2.6 [1.2-5.8]). Maternal coffee consumption during pregnancy was associated with childhood acute leukemia, ORs increasing in ALL with coffee consumption (OR=1.1 [0.7-1.8], OR=2.4 [1.3-4.7] and OR=3.1 [1.0-9.5], respectively, for < or =3, 4-8 and >8 cups/day). No association with maternal smoking during pregnancy or parental smoking before or after the index child's birth was observed.

DISCUSSION

Our results suggest an association with maternal alcohol and coffee drinking during pregnancy and call for further investigations. Besides, the present study does not support the hypothesis of an increase in the risk of childhood leukemia related to parental smoking.

Incidence and Characteristics of Childhood Hodgkin’s Lymphoma in Greece: A Nationwide Study (Greece)

OBJECTIVES

To estimate the incidence and epidemiological profile of childhood (0-14 years) Hodgkin's lymphoma in Greece derived by the network of childhood Hematology-Oncology departments on the basis of all 95 newly diagnosed cases during a seven-year period.

METHODS

Seventy-one of these cases were individually age and gender matched to an equal number of controls.

RESULTS

The incidence of childhood Hodgkin Lymphoma reached a relatively high figure of 7.8 per million children-years, with an age distribution (2.2 for children 0-4; 6.3 for those 5-9 and 13.9 for those 10-14-years-old) and male to female ratio (1.7:1) similar to that reported from other cancer registries. Childhood Hodgkin's lymphoma was more common among children living in less crowded quarters (odds ratio (OR): 6.5 and 95% confidence intervals (95% CI): 1.4-30.7), among those who have changed residence 60 to 18 months before the onset of the index disease (OR: 4.4, and 95% CI = 1.4-14.0), among those whose families owned a cat (OR: 5.5, 95% CI = 1.2-25.6) but not among those whose families owned a dog and marginally more common, among those with a history of infectious mononucleosis (OR: 5.0, 95% CI = 0.6-42.8).

CONCLUSIONS

Our results point to infectious agent(s) as playing an etiological role but do not allow discrimination among the delayed establishment of the herd immunity hypothesis, the population mixing hypothesis or that invoking transmission of the agent(s) from the non-human reservoir.

Childhood leukaemia, polymorphisms of metabolism enzyme genes, and interactions with maternal tobacco, coffee and alcohol consumption during pregnancy

Metabolic polymorphisms may influence the risk of childhood leukaemia related to maternal tobacco, coffee or alcohol consumption. The data were extracted from a case-control study including 280 cases of acute leukaemia and 288 controls. Blood sampling was obtained for a representative subset of 219 cases and 105 controls. Gene-environment interactions were estimated using both case-control and case-only analyses. The polymorphisms of CYP1A1, GSTM1, GSTP1, GSTT1 and NQO1 were not associated with the risk of leukaemia. The slow EPHX1 allele was negatively associated with childhood leukaemia while an inverse non-significant association was observed with the fast EPHX1 allele. Maternal smoking during pregnancy was not related to leukaemia, but an interaction was observed in the case-only analysis with CYP1A1*2A variant allele (odds ratio (OR) 2.2 [1.0-4.9]) and with GSTM1 deletion (OR 2.3 [1.2-4.4]). Conversely, coffee drinking interacted negatively with NQO1 polymorphism in the case-only analysis (OR 0.6 [0.3-1.2] and 0.4 [0.1-1.0] for light and heavy coffee consumptions, respectively). This study suggests that maternal smoking may be a risk factor for leukaemia in children who carry CYP1A1 or GSTM1 genotypes, which might increase reactive metabolites of polycyclic aromatic hydrocarbons.

Socioeconomic status and childhood leukaemia: a review

BACKGROUND

A long-held view links higher socioeconomic status (SES) to higher rates of childhood leukaemia. Some recent studies exhibit associations in the opposite direction.

METHODS

We reviewed journal literature through August 2002 for associations between childhood leukaemia and socioeconomic measures. We determined the direction of each association and its P-value. We described the results with regard to study design, calendar period, geographic locale, and level of the socioeconomic measures (individual or ecological). For measures with sufficient number of results, we computed summary P-values across studies.

RESULTS

Case-control studies conducted in North America since 1980 have involved subject interviews or self-administered questionnaires and have consistently reported inverse (negative) associations of childhood leukaemia with individual-level measures of family income, mother's education, and father's education. In contrast, associations have been consistently positive with father's occupational class in record-based case-control studies and with average occupational class in ecological studies.

CONCLUSIONS

Connections of SES measures to childhood leukaemia are likely to vary with place and time. Validation studies are needed to estimate SES-related selection and participation in case-control studies. Because different socioeconomic measures (such as income and education) and individual-level and ecological-level measures may represent different risk factors, we advise researchers to report these measures separately rather than in summary indices of social class.

Ethnic difference in daycare attendance, early infections, and risk of childhood acute lymphoblastic leukemia

A role for infectious agents has been proposed in the etiology of childhood acute lymphoblastic leukemia (ALL), particularly for common ALL (c-ALL; ALL diagnosed in children ages 2-5 years and expressing CD10 and CD19 surface antigens). We evaluated the possible etiologic role of daycare attendance (a proxy measure for exposure to infectious agents) and infections during infancy in the Northern California Childhood Leukemia Study. A total of 294 incident ALL cases (ages 1-14 years) and 376 individually matched controls were included in this analysis. In non-Hispanic White children, daycare attendance measured by child-hours was associated with a significantly reduced risk of ALL. Compared with children who did not attend any daycare, the odds ratio (OR) for those who had >5,000 child-hours during infancy was 0.42 [95% confidence interval (95% CI), 0.18-0.99] for ALL and 0.33 (95% CI, 0.11-1.01) for c-ALL. Test for trend is also significant, which supports a dose-response relationship. The magnitude of effect associated with the same number of child-hours was stronger for daycare attendance during infancy than for daycare attendance before diagnosis. In addition, self-reported ear infection during infancy was associated with a significantly reduced risk of c-ALL (OR, 0.32; 95% CI, 0.14-0.74) in non-Hispanic White children. In Hispanic children, no association was observed among daycare attendance, early infections, and risk of childhood ALL or c-ALL. These results offer indirect yet strong support for the infectious disease hypothesis in the etiology of ALL in non-Hispanic White children and highlight an important ethnic difference.

Review of case-control studies related to breastfeeding and reduced risk of childhood leukemia

OBJECTIVE

To conduct a systematic review to evaluate the evidence for the effect of breastfeeding on the risk of developing childhood leukemia.

REVIEW METHODS

We sought studies providing data regarding the association of breastfeeding and occurrence of childhood leukemia. Studies were identified by using Medline, HHS Blueprint for Action on Breastfeeding, US Department of Health and Human Services Office on Women's Health, Cochrane Database of Systematic Reviews, National Centre for Reviews and Dissemination, reference lists, and national experts. Methodologic quality was evaluated for each study by using criteria from the US Preventive Services Task Force and the National Health Service Centre for Reviews and Dissemination.

RESULTS

We reviewed 111 citations to identify 32 potentially eligible full-text articles. Of the 10 studies reviewed, only 4 were sufficient to provide at least fair-quality evidence regarding the association between maternal breastfeeding and childhood leukemia. Studies conflicted regarding the protective effect of breastfeeding on childhood leukemia. In the 2 largest and highest quality studies, breastfeeding was associated with a significant risk reduction in one study with longer breastfeeding duration, reflecting greater protection, and a nonsignificant but suggestive difference in the other. Taken together, half of the studies associated breastfeeding with a lower risk of acute lymphocytic leukemia.

CONCLUSIONS

There are few high-quality studies that examine the potential for a protective effect of breastfeeding for childhood leukemia. Furthermore, the few studies that exist disagree regarding the association. It is estimated that the United States spends 1.4 billion dollars annually on the treatment of childhood leukemia. Patients, clinicians, and policy makers do not have the data that they need to make decisions regarding this important potential preventive measure.

Is atopy a protective or a risk factor for cancer? A review of epidemiological studies

OBJECTIVE

There is an ongoing debate whether there is a link between a history of atopy and cancer risk. The purpose of this paper is to review the published epidemiological studies on the association between atopy and the risk of cancers.

METHODS

Through an electronic search (January 1986-April 2004) with an additional review of cited references, we identified studies with quantitative data on the relation of atopy (irrespective of its definition or subtype) to cancer (different cancer sites).

RESULTS

The protective effect of atopy in colorectal cancer has been observed consistently in the case-control studies, but not in cohort studies. A consistent inverse association between self-reported atopy and glioma risk has been shown, but there is absence of such an association for meningioma. In most studies, the risk of leukaemia, in particular childhood leukaemia, tends to be lower among people with a history of atopy. Studies, which looked at, the association between atopic diseases and risk of cancers of pancreatic, breast, lymphoma showed varying outcomes. Most studies on the atopy-pancreatic cancer relation suggested an inverse association. For lymphoma, most studies have shown no substantial association. Overall evidence indicates an increased risk of lung cancer among persons with a history of asthma.

CONCLUSION

Despite the mixed results, the emerging picture from most of the currently available epidemiological data indicate that atopic disease is associated with a reduced risk for cancer. Further research should focus on a more carefully defined 'atopy' status and manifestation of different atopic diseases, to advance our understanding of the role that allergies might play in the risk of developing cancer.

Breastfeeding patterns and risk of childhood acute lymphoblastic leukaemia

The risk of childhood acute lymphoblastic leukaemia (ALL) was investigated in relation to breastfeeding patterns in the Northern California Childhood Leukaemia Study. Data collected by self-administered and in-person questionnaires from biological mothers of leukaemia cases (age 0-14 years) in the period 1995-2002 were matched to birth certificate controls on date of birth, sex, Hispanic ethnic status, and maternal race. Ever compared to never breastfeeding was not associated with risk of ALL at ages 1-14 years (odds ratio=0.99; 95% CI=0.64-1.55) and ages 2-5 years (OR=1.49; 95% CI=0.83-2.65). Various measures of breastfeeding duration compared to absence of breastfeeding also had no significant effect on risk. Complimentary feeding characteristics such as type of milk/formula used and age started eating solid foods among breastfed children were not associated with ALL risk. This study provides no evidence that breastfeeding affects the occurrence of childhood ALL.

Maternal diet and acute lymphoblastic leukemia in young children

Because leukemia clone-specific chromosomal abnormalities are present at birth in children who later develop leukemia, it has been hypothesized that maternal factors, including nutrition during pregnancy, might affect the risk of acute lymphoblastic leukemia (ALL) among young children. We have evaluated this hypothesis in a nationwide case-control study of ALL among children ages 12 to 59 months in Greece. Children (n=131) with ALL were gender and age matched to control children (n=131) hospitalized for minor conditions between 1999 and 2003. The mothers of the children were interviewed in person by trained interviewers who used an extensive food frequency questionnaire addressing diet during the index pregnancy. The analysis was done by modeling the data through conditional logistic regression, also controlling for total energy intake and possible confounding factors. Odds ratios (OR) and 95% confidence intervals (95% CI) were expressed per quintile increase of maternal intake during pregnancy of the specified food group. The risk of ALL in the offspring was lower with increased maternal intake of fruits (OR, 0.72; 95% CI, 0.57-0.91), vegetables (OR, 0.76; 95% CI, 0.60-0.95), and fish and seafood (OR, 0.72; 95% CI, 0.59-0.89) and higher with increased maternal intake of sugars and syrups (OR, 1.32; 95% CI, 1.05-1.67) and meat and meat products (OR, 1.25; 95% CI, 1.00-1.57). Children of women who tend to consume during their pregnancies what is currently considered to be a healthy diet maybe at lower risk of ALL.

Vaccination history and risk of childhood leukaemia

BACKGROUND

Previous studies on vaccination and childhood leukaemia generated inconsistent results.

METHODS

In the Northern California Childhood Leukaemia Study, a case-control study with incident cases and matched birth certificate controls, detailed written vaccination records were collected. A total of 323 cases aged 0-14 years at diagnosis and 409 controls were included in this analysis. All vaccinations were censored on the reference date (date of diagnosis for cases and the corresponding date for matched controls). Conditional logistic regression analysis was conducted, adjusting for potential confounding factors. A primary variable of interest is the number of administrations (doses) of various types of vaccines.

RESULTS

Vaccinations against diphtheria, pertussis, tetanus, poliomyelitis, measles, mumps, and rubella were not associated with the risk of leukaemia. The odds ratio for each dose of Haemophilus influenzae type b (Hib) vaccine was 0.81 (95% CI 0.68-0.96). Compared with children who received two or fewer doses of Hib vaccine, those who received three or more doses had a significantly reduced risk of childhood leukaemia (odds ratio = 0.55, 95% confidence interval 0.32-0.94). The number of doses of hepatitis B vaccine received was not associated with leukaemia risk.

CONCLUSIONS

Hib vaccination is associated with a reduced risk of childhood leukaemia. Future studies with detailed exposure assessment and large sample sizes are needed to further address the role of vaccinations in the etiology of childhood leukaemia.

Day care in infancy and risk of childhood acute lymphoblastic leukaemia: findings from UK case-control study

OBJECTIVE

To test the hypothesis that reduced exposure to common infections in the first year of life increases the risk of developing acute lymphoblastic leukaemia. Design and setting The United Kingdom childhood cancer study (UKCCS) is a large population based case-control study of childhood cancer across 10 regions of the UK.

PARTICIPANTS

6305 children (aged 2-14 years) without cancer; 3140 children with cancer (diagnosed 1991-6), of whom 1286 had acute lymphoblastic leukaemia (ALL).

MAIN OUTCOME MEASURE

Day care and social activity during the first year of life were used as proxies for potential exposure to infection in infancy.

RESULTS

Increasing levels of social activity were associated with consistent reductions in risk of ALL; a dose-response trend was seen. When children whose mothers reported no regular activity outside the family were used as the reference group, odds ratios for increasing levels of activity were 0.73 (95% confidence interval 0.62 to 0.87) for any social activity, 0.62 (0.51 to 0.75) for regular day care outside the home, and 0.48 (0.37 to 0.62) for formal day care (attendance at facility with at least four children at least twice a week) (P value for trend < 0.001). Although not as striking, results for non-ALL malignancies showed a similar pattern (P value for trend < 0.001). When children with non-ALL malignancies were taken as the reference group, a significant protective effect for ALL was seen only for formal day care (odds ratio = 0.69, 0.51 to 0.93; P = 0.02). Similar results were obtained for B cell precursor common ALL and other subgroups, as well as for cases diagnosed above and below age 5 years.

CONCLUSION

These results support the hypothesis that reduced exposure to infection in the first few months of life increases the risk of developing acute lymphoblastic leukaemia.

Hypermethylation of CpG islands in the promoter region of the p15INK4B gene in childhood acute leukaemia

It has been reported that the cyclin-dependent kinase inhibitor (CDKI) gene p15INK4B is frequently inactivated by genetic alterations and may be responsible for various malignant tumours. Another way of inactivation of this CDKI is by hypermethylation of 5'CpG islands in the promoter region of the p15INK4B gene and this inactivation seems to be a frequent event in various haematological malignancies. In the present study, we investigated the methylation status of the p151NK4B gene to clarify its role in the pathogenesis of childhood acute myeloid (AML) and acute lymphoblastic leukaemia (ALL). The study included 23 cases of B-cell origin ALL, 13 cases of T-cell origin ALL, 32 cases of AML, and 10 apparently healthy controls. Hypermethylation was studied by methylation-specific polymerase chain reaction. Hypermethylation of the p15INK4B gene was more frequent in cases with T-cell origin ALL (46.2%), but similar among children with B-cell origin ALL (13.0%) and AML (18.8%). Hypermethylation of p15INK4B may be involved in the pathogenesis of T-cell origin ALL, but not in that of AML or B-cell origin ALL.

Perinatal and reproductive factors: a report on haematological malignancies from the UKCCS

The United Kingdom Childhood Cancer Study was designed to examine the potential aetiological role of a range of perinatal and reproductive factors. Our use of clinical records permitted a more exact characterisation of reproductive events than is possible in investigations that rely on self-reporting; and the increased specificity with which antecedent events were measured produced more precise risk estimates, albeit ones based on progressively smaller numbers. Information on the conduct of this component of the study and results for 1485 children with haematological malignancies and 4864 controls are presented. The 'find' rate for obstetric records was high at 86% for cases, with 81% having information on both matched controls. Associations were seen for severe hyperemesis (Odds Ratio=3.6, 95%Confidence Interval=1.3-10.1, for all leukaemias), polyhydramnios (OR=4.0, 95%CI=1.5-10.3, for acute myeloid leukaemia (AML)), anaemia (haemoglobin <10 g, OR=2.6, 95%CI=1.7-4.1, for AML), and pre-eclampsia (OR=1.7, 95%CI=1.1-2.7, for non-Hodgkin's lymphoma). Babies who developed leukaemia were heavier at birth (>4000 g, OR=1.2, 95%CI=1.0-1.4), as were their older siblings (>4000 g, OR=1.4, 95%1.0-1.9). Mothers' whose children developed common B-cell precursor acute lymphoblastic leukaemia (ALL) were more likely to have had a previous molar pregnancy (OR=5.2, 95%CI=1.9-14.7). Gender-specific analysis revealed that findings often differed markedly for boys and girls; and, in common with other reports, strong associations with Down's syndrome were seen for both ALL and AML.

Breast-feeding and childhood cancer: A systematic review with metaanalysis

It has been suggested that breast milk may play a role in the prevention of certain childhood cancers. We undertook a systematic review of published studies investigating the association between breast-feeding and childhood cancers using Medline (1966 to June 2004), supplemented with auto alerts and manual searches. Analyses are based on odds ratios for specific cancers among those ever breast-fed compared with those never breast-fed, pooled using random-effects models. Forty-nine publications were potentially relevant; of these, 26 provided odds ratio estimates for at least one childhood cancer outcome and were included in metaanalyses. Overall, 92% of the studies were case-control studies, 85% relied on long-term recall of feeding history, only 8% examined breast-feeding exclusivity and control response rates were under 80% in over half. Metaanalyses suggested lower risks associated with having been breast-fed of 9% (95% CI = 2-16%) for acute lymphoblastic leukemia, 24% (3-40%) for Hodgkin's disease and 41% (22-56%) for neuroblastoma, with little between-study heterogeneity. The estimates for Hodgkin's disease and neuroblastoma, however, were driven by single studies. There was little evidence that breast-feeding was associated with acute nonlymphoblastic leukemia, non-Hodgkin's lymphoma, central nervous system cancers, malignant germ cell tumors, juvenile bone tumors, or other solid cancers. In conclusion, ever having been breast-fed is inversely associated with acute lymphoblastic leukemia, Hodgkin's disease and neuroblastoma in childhood, but noncausal explanations are possible. Even if causal, the public health importance of these associations may be small. Our estimates suggest that increasing breast-feeding from 50% to 100% would prevent at most 5% of cases of childhood acute leukemia or lymphoma. (c) 2005 Wiley-Liss, Inc.

An infectious aetiology for childhood acute leukaemia: a review of the evidence

There are three current hypotheses concerning infectious mechanisms in the aetiology of childhood leukaemia: exposure in utero or around the time of birth, delayed exposure beyond the first year of life to common infections and unusual population mixing. No specific virus has been definitively linked with childhood leukaemia and there is no evidence to date of viral genomic inclusions within leukaemic cells. The case-control and cohort studies have revealed equivocal results. Maternal infection during pregnancy has been linked with increased risk whilst breast feeding and day care attendance in the first year of life appear to be protective. There is inconclusive evidence from studies on early childhood infectious exposures, vaccination and social mixing. Some supportive evidence for an infectious aetiology is provided by the findings of space-time clustering and seasonal variation. Spatial clustering suggests that higher incidence is confined to specific areas with increased levels of population mixing, particularly in previously isolated populations. Ecological studies have also shown excess incidence with higher population mixing. The marked childhood peak in resource-rich countries and an increased incidence of the childhood peak in acute lymphoblastic leukaemia (ALL) (occurring at ages 2-6 years predominantly with precursor B-cell ALL) is supportive of the concept that reduced early infection may play a role. Genetically determined individual response to infection may be critical in the proliferation of preleukaemic clones as evidenced by the human leucocyte antigen class II polymorphic variant association with precursor B-cell and T-cell ALL.

Breastfeeding and the risk of childhood leukemia: a meta-analysis

OBJECTIVE

The authors used a meta-analytic technique to (1) quantify the evidence of an association between duration of breastfeeding and risk of childhood acute lymphoblastic leukemia (ALL) or acute myeloblastic leukemia (AML), (2) assess the influence of socioeconomic status (SES) on any such associations, and (3) discuss the implications of these findings for the evaluation of whether breastfeeding reduces the risk of childhood leukemia.

METHODS

A fixed effects model was employed to systematically combine the results of 14 case-control studies addressing the effect of short-term (< or = 6 months) and long-term (>6 months) breastfeeding on the risk of childhood ALL and/or AML. Subgroup analyses of studies that did and did not adjust for SES were also performed.

RESULTS

A significant, negative association was observed between long-term breastfeeding and both ALL risk (odds ratio [OR]=0.76; 95% confidence interval [CI] 0.68, 0.84) and AML risk (OR=0.85; 95% CI 0.73, 0.98). Short-term breastfeeding was similarly protective for ALL and AML. Results for studies that adjusted and did not adjust for SES were not significantly different from the results for the 14 studies combined.

CONCLUSIONS

This meta-analysis showed that both short-term and long-term breastfeeding reduced the risk of childhood ALL and AML, suggesting that the protective effect of breastfeeding might not be limited to ALL as earlier hypothesized. Potential bias introduced by different participation rates for case and control samples that differed in SES can be minimized by implementing larger case-control studies with SES-matched, population-based controls.

Socioeconomic status and risk of childhood leukaemia in Denmark

AIMS

The aim of this study was to assess the influence of socioeconomic status on the risk of childhood leukaemia.

METHODS

A matched case-control design was used. The study population comprised all children (0-14 years old) born and reported to the Danish Cancer Registry between 1976 and 1991 for a diagnosis of leukaemia (n=377). Controls were selected from the Central Population Registry and matched by sex, age, and time of birth. Each child was assigned three categories of socioeconomic status, one corresponding to the annual average income in the municipality of residence at the time of birth, another corresponding to that at the time of diagnosis, and, finally, each family was assigned one of five social classes by use of the job titles of the parents. Conditional logistic regression was used to estimate the effect of socioeconomic status on the risk of childhood leukaemia.

RESULTS

Children born in low-income municipalities had a significantly increased risk of leukaemia (RR=2.71; 95% CI=1.41-5.21; p=0.003), which was higher among those who received their diagnosis before age five (RR=3.43; 95% CI=1.52-7.74; p=0.003). Neither individual social class nor the socioeconomic status of the residential area at the time of diagnosis was convincingly associated with the risk of childhood leukaemia.

CONCLUSIONS

The results suggest that socioeconomic factors associated with community characteristics rather than individual lifestyle are related to the risk of childhood leukaemia and that these factors act early in life.

Towards an integrated model for breast cancer etiology: the crucial role of the number of mammary tissue-specific stem cells

Perinatal events and conditions, notably birth weight, are associated with breast cancer risk in offspring, and correlates of mammary gland mass are predictors of breast cancer risk. These findings may be interpreted as indicating that high levels of estrogens and components of the insulin-like growth factor system during pregnancy favour the generation of mammary tissue-specific stem cells, and that the number of these cells, which is positively associated with mammary gland mass, is an important determinant of breast cancer risk. Perinatal events and conditions may also affect risk for other malignancies, but the evidence in the case of breast cancer is prominent, possibly because estrogens and the insulin-like growth factor system are both involved in breast cancer etiology and affect birth weight.

An integrated evaluation of socioeconomic and clinical factors in the survival from childhood acute lymphoblastic leukaemia: a study in Greece

An evaluation of the role of socioeconomic factors in the survival of children with leukaemia, controlling for major clinical prognostic indicators, has been attempted in very few studies and the role of these factors may be different in various cultural settings. Our investigation aims to study the independent role of socioeconomic factors on the prognosis of childhood acute lymphoblastic leukaemia (ALL) in Greece. During a 7-year period (1996-2002) 293 cases of incident ALL were diagnosed and followed up in four Childhood Haematology-Oncology Units, which covered over half of all childhood ALL cases nationwide. At the time of diagnosis, information concerning age, gender, maternal schooling, maternal marital status, sibship size, distance of residence from the treating centre, attendance of day care centre and clinical information was recorded. The influence of these factors on survival was studied by modelling the data through Cox's proportional-hazards regression. After adjustment for clinical prognostic factors, children of mothers who were not currently married, were of low educational level or were living far from the treating centre tended to have lower survival (P-values 0.02, 0.14 and 0.08, respectively). There was also evidence that two factors that are predictive of disease occurrence, that is sibship size and attendance of day care centre, may also predict survival (P-values 0.04 and 0.26, respectively). In conclusion, socioeconomic factors are likely to influence survival from ALL at least in some sociocultural contexts. Moreover, there is evidence that factors that could affect incidence of ALL through modulation of herd immunity may also have prognostic implications for this disease.

Medically recorded allergies and the risk of childhood acute lymphoblastic leukaemia

Data on five allergic conditions were abstracted from the medical records of 180 cases of childhood acute lymphoblastic leukaemia (ALL) and 718 matched controls. Odds Ratios (OR) and 95% Confidence Intervals (CI) were estimated for composite variables and for individual allergies using conditional logistic regression modelling. Allergies were divided into late and early diagnoses (those made within the year before the matched case's ALL diagnosis and those made earlier, respectively). Among the early diagnoses, atopy or hives was significantly associated with ALL (OR=2.20; 95% CI: 1.16-4.16). Significant associations were found for late diagnoses of atopy or hives (OR=3.78; 95% CI: 1.00-14.29) and of asthma (OR=3.10; 95% CI: 1.39-6.95). None of the other allergic conditions were associated with ALL. These results are contrary to those of prior studies of childhood ALL and allergy.

Infectious diseases in the first year of life, perinatal characteristics and childhood acute leukaemia

The objective of the present study was to investigate the role of early common infections and perinatal characteristics in the aetiology of childhood common leukaemia. A case–control study was conducted from 1995 to 1998 in France, and included 473 incident cases of acute leukaemia (AL) (408 acute lymphoblastic leukaemia (ALL), 65 acute myeloid leukaemia (AML) age-, sex- and region-matched with 567 population-based controls. Data on the medical history of the child and his/her environment were collected using self-administered questionnaires. Analyses were conducted using nonconditional logistic regression. A slight negative association with early infections was observed (OR=0.8; 95% CI (0.6–1.0)). The association was stronger for early gastrointestinal infections. Early day-care was found to be associated with a decreased risk of AL (OR=0.6; 95% CI (0.4–0.8) and OR=0.8; 95% CI (0.5–1.2) for day-care starting before age 3 months and between 3 and 6 months, respectively). No association with breast-feeding was observed, irrespective of its duration. A birth order of 4 or more was associated with a significantly increased risk of AL (OR=2.0; 95% CI (1.1–3.7) with ALL). A history of asthma was associated with a decreased risk of ALL (OR 0.5; 95% CI (0.3–0.90). Although the results regarding birth order and breast-feeding do not fit with Greaves' hypothesis, the study supports the hypothesis that early common infections may play a protective role in the aetiology of childhood leukaemia, although this effect was not more marked for common ALL.

Growth velocity during the first postnatal week of life is linked to a spurt of IGF-I effect

There is adequate evidence that growth during the perinatal period is linked to the risk of several adult onset diseases, and recent findings indicate that the insulin-like growth factor (IGF) system is involved in prenatal growth, as reflected in birthweight. However, whether major components of the IGF system are involved in the immediate post-natal growth has not been studied. Maternal questionnaires were completed, and laboratory measurements of several variables, including IGF-I, IGF-II and IGF-binding protein-3 (IGFBP-3), were made for a total of 331 apparently healthy full-term newborns, from whom routine blood samples were taken during the first 5 days of their life. Birthweight and weight at the time of bleeding were among the recorded variables, and the difference divided by the age in days of the newborn was considered as reflecting immediate postnatal growth velocity. Immediate postnatal growth velocity was strongly positively associated with IGF-I. The squared adjusted correlation coefficient was 0.29 when IGF-I was incorporated in the model predicting postnatal growth velocity but was only 0.08 when IGF-I was excluded. In contrast, IGF-II and IGFBP-3 had no effect on postnatal growth velocity. It thus appears that IGF-I underlies growth during the immediate postnatal period. To the extent that perinatal growth may affect adult onset diseases, the findings of this study suggest that the action of IGF-I during the immediate postnatal period may represent a process of major importance.

Parental medication use and risk of childhood acute lymphoblastic leukemia

BACKGROUND

Few studies have examined the risk of childhood acute lymphoblastic leukemia (ALL) associated with parental medication use. As part of a large case-control study conducted by the Children's Cancer Group, we evaluated the association between maternal and paternal medication use and the risk of ALL in offspring.

METHODS

Information on selected medication use in the year before and during the index pregnancy was obtained by telephone interview. Participants included 1842 children of 14 years or younger with newly diagnosed and immunophenotypically defined ALL and 1986 individually matched controls. Data were analyzed using logistic regression models and stratified by immunophenotypes of ALL and age at diagnosis of cases.

RESULTS

After adjusting for potential confounders and other medication use, we found that maternal use of vitamins (odds ratio [OR] = 0.7, 99% confidence interval [CI]: 0.5-1.0) and iron supplements (OR = 0.8, 99% CI: 0.7-1.0) only during the index pregnancy was associated with a decreased risk of ALL. Parental use of amphetamines or diet pills and mind-altering drugs before and during the index pregnancy was related to an increased risk of childhood ALL, particularly among children where both parents reported using these drugs (OR = 2.8, 99% CI: 0.5-15.6 for amphetamines or diet pills, OR = 1.8, 99% CI: 1.1-3.0 for mind-altering drugs). Stratified analyses showed that maternal use of antihistamines or allergic remedies and parental use of mind-altering drugs were strongly associated with infant ALL, whereas patterns of association between childhood ALL and parental medication use did not influence markedly the immunophenotypic subgroup of ALL.

CONCLUSIONS

The findings of this study suggest that certain parental medication use immediately before and during the index pregnancy may influence risk of ALL in offspring.

Recent thymic emigrants and prognosis in T- and B-cell childhood hematopoietic malignancies

The concentration of T-cell receptor rearrangement excision DNA circles (TRECs) in peripheral blood mononuclear cells (PBMCs) is currently known to be a marker of recent thymic emigrants. We evaluated the hypothesis that TREC values would be lower in childhood T-cell hematopoietic malignancies than in childhood B-cell acute lymphoblastic leukemia (ALL) or healthy controls because the former category may reflect compromised thymic function. From the Greek national childhood leukemia/lymphoma database we obtained all 30 available T-cell leukemia/non-Hodgkin's lymphoma cases, 30 age- and sex-matched childhood B-cell origin cases of ALL and 60 healthy hospital controls. We compared TREC levels in PBMCs using a real-time PCR assay. There was highly significant reduction of TREC values in children with T-cell malignancies (median 3,100 TRECs/10(6) PBMCs), whereas children with B-cell origin ALL had slightly but nonsignificantly lower TREC values compared to healthy children (medians 19,300 and 22,500 TRECs/10(6) PBMCs, respectively). During a median follow-up period of about 19 months, only 4 children died. All of them had a T-cell hematopoietic malignancy and relatively low TREC values. The number of TRECs was higher among healthy girls than among healthy boys, and a similar pattern was evident in T-cell malignancies. It appears that there is a pattern of concordance of high TREC values with better disease prognosis in hematologic childhood malignancies. This applies to specific disease entities with better prognosis (B-cell origin ALL having higher TREC values than T-cell leukemia/lymphoma) and to gender, another important predictor of prognosis conditional on disease entity (girls having higher TREC values than boys); however, it may also be true for the survival of individual patients. These preliminary findings can be used as hypothesis-generating indications that should be confirmed in larger data sets.

Daycare attendance and risk of childhood acute lymphoblastic leukaemia

The relationship between daycare/preschool ("daycare") attendance and the risk of acute lymphoblastic leukaemia was evaluated in the Northern California Childhood Leukaemia Study. Incident cases (age 1-14 years) were rapidly ascertained during 1995-1999. Population-based controls were randomly selected from the California birth registry, individually matched on date of birth, gender, race, Hispanicity, and residence, resulting in a total of 140 case-controls pairs. Fewer cases (n=92, 66%) attended daycare than controls (n=103, 74%). Children who had more total child-hours had a significantly reduced risk of ALL. The odds ratio associated with each thousand child-hours was 0.991 (95% confidence interval (CI): 0.984-0.999), which means that a child with 50 thousand child-hours (who may have, for example, attended a daycare with 15 other children, 25 h per week, for a total duration of 30.65 months) would have an odds ratio of (0.991)(50)=0.64 (95% CI: 0.45, 0.95), compared to children who never attended daycare. Besides, controls started daycare at a younger age, attended daycare for longer duration, remained in daycare for more hours, and were exposed to more children at each daycare. These findings support the hypothesis that delayed exposure to common infections plays an important role in the aetiology of childhood acute lymphoblastic leukaemia, and suggest that extensive contact with other children in a daycare setting is associated with a reduced risk of acute lymphoblastic leukaemia.

Childhood acute lymphoblastic leukemia associated with parental alcohol consumption and polymorphisms of carcinogen-metabolizing genes

BACKGROUND

Limited information is available on the association of parental consumption of alcohol prior to and during pregnancy with the risk of childhood leukemia, as well as for the potentially modifying role of genetic polymorphisms.

METHODS

We conducted a population-based, case-control study of 491 incident cases of acute lymphoblastic leukemia age 0-9 years and matched on age and sex to 491 healthy controls. Cases were identified at tertiary care centers in the Province of Québec between 1980 and 1993. Each parent was interviewed separately about alcohol consumption habits. We also used a case-only design with 186 cases to estimate interaction odds ratios between prenatal exposure and child DNA variants in the GSTM1 and CYP2E1 genes.

RESULTS

The adjusted odds ratio for any maternal consumption during pregnancy was 0.7 (95% confidence interval = 0.5-0.9). The interaction odds ratios for the GSTM1 null genotype during third pregnancy trimester was 2.4 (95% confidence interval = 1.1-5.4); the interaction odds ratio for CYP2E1 variant G-1295C (or allele *5) during the nursing period was 4.9 (95% confidence interval = 1.5-16.7).

CONCLUSIONS

The observed association with maternal alcohol consumption during pregnancy could be due to the potential chemopreventive effects of flavonoids found in wine and beer. These possible effects of alcohol may be at least partially genetically determined, although data are preliminary.

Childhood malignancy and maternal diabetes or other auto-immune disease during pregnancy

Among 4380 children born in 1987-1997 of women with a diagnosis of diabetes and alive at the age of one, 10 were registered in the Swedish Cancer Registry before the end of 1998. The odds ratio for having a childhood cancer after maternal diabetes, stratified for year of birth, maternal age, parity, multiple birth, and 500 g birth weight class was 2.25 (95%CI 1.22-4.15). Among 5842 children born during the period 1973-1997 whose mothers had other auto-immune diseases (SLE, rheumatoid arthritis, Crohn, ulcerous colitis, multiple sclerosis or thyroiditis), the number of observed childhood cancers (9) was close to that expected (8.5). Maternal diabetes but not other auto-immune diseases may be a risk factor for childhood cancer.

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

We conducted a case-control study to investigate the role of early infections in the aetiology of childhood acute leukaemias. The study included 280 incident cases (240 acute lymphoblastic leukaemia and 40 acute non-lymphoblastic leukaemia) and 288 hospital controls, frequency matched by age, gender, hospital, catchment area of the hospital and ethnic origin. Data were obtained from standardised face-to-face interviews of the mothers. The interviews included questions on early common infections, day-care attendance, breast-feeding, birth order and infantile diseases. Odds ratios were estimated using an unconditional regression model including the stratification variables, parental socio-economic status and perinatal characteristics. Birth order was not associated with childhood leukaemia (acute lymphoblastic or acute non-lymphoblastic). A statistically-significant inverse association was observed between childhood leukaemia and day-care attendance (odds ratio=0.6, 95% Confidence Interval=(0.4-1.0)), repeated early common infections (> or = 4 per year before age two, odds ratio=0.6 (0.4-1.0)), surgical procedures for ear-nose-throat infections before age two (odds ratio=0.5 (0.2-1.0)) and prolonged breast-feeding (> or = 6 months, odds ratio=0.5 (0.2-1.0)). In the multivariate model including day-care attendance, early common infections and breast-feeding, results concerning breast-feeding remained unchanged. A statistically significant interaction between day-care attendance and repeated early common infections was observed. When the interaction was taken into account, the simple effects of day-care and early common infections disappeared (odds ratio=1.1 (0.5-2.3) and odds ratio=0.8 (0.5-1.3), respectively) while the joint effect of day-care attendance and early common infections was negatively associated with childhood leukaemia (odds ratio=0.3 (0.1-0.8)). All the above associations were observed both for acute lymphoblastic leukaemia and acute non-lymphoblastic leukaemia. Our results support Greaves' hypothesis, even though they are not specific of common leukaemia.

Preliminary study on DNA damage in non breast-fed infants

BACKGROUND

There are many advantages of human milk for infants, including protection against cancer development and the advantages have been emphasized in several studies. In this study, infants fed by human milk has been compared with those fed by cow's milk concerning DNA damage.

METHODS

The level of genetic damage in the peripheral blood lymphocytes of infants who were fed mainly by cow's milk and breast milk has been studied by sister chromatid exchange (SCE) analysis, which is a sensitive measurement of chromosomal damage. Each group consisted of 30 infants, whose ages ranged from 9 to 12 months.

RESULTS

A significant increase (P < 0.0001) was found in the frequencies of SCE of infants not breast-fed (n = 30, mean SCE/cell +/- SD: 8.66 +/- 1.15) compared to those who were breast-fed (n = 30, mean SCE/cell +/- SD: 4.93 +/- 0.82).

CONCLUSION

To our knowledge, there has been no published study investigating SCE ratio regarding DNA damage in infants not breast-fed. Molecular mechanism of DNA damage caused by the absence of human milk protection is a subject of future investigations.

Maternal folate supplementation in pregnancy and protection against acute lymphoblastic leukaemia in childhood: a case-control study

BACKGROUND

Acute lymphoblastic leukaemia is the most common childhood cancer in more-developed countries but it has few recognised risk factors or preventive measures. We aimed to determine and assess the risk factors associated with this disease.

METHODS

From 1984 to 1992, we investigated known and suspected risk factors for common acute lymphoblastic leukaemia diagnosed in a population-based case-control study of children aged 0-14 years in Western Australia. 83 children in the study group came from the sole referral centre for paediatric cancer in the state and 166 controls matched for age and sex were recruited through a postal survey of people randomly selected from the state electoral roll. We interviewed mothers of 83 study and 166 control children (82% and 74%, respectively, of those eligible). Fathers completed a self-administered questionnaire.

FINDINGS

We recorded a protective association between iron or folate supplementation in pregnancy and risk of common acute lymphoblastic leukaemia in the child (odds ratio 0.37 [95% CI 0.21-0.65]; p=0.001). For iron alone, the odds ratio was 0.75 (0.37-1.51); only one mother took folate without iron. Further analyses of folate use with or without iron (0.40; 0.21-0.73) showed that the protective effect varies little by time of first use of supplements or for how long they were taken. The association was not weakened by adjustment for potentially confounding variables.

INTERPRETATION

Our results, though unexpected, suggest that folate supplementation in pregnancy reduces the risk of common acute lymphoblastic leukaemia in the child.

Breastfeeding and childhood cancer

The relationship between childhood cancer and having been breastfed in infancy was investigated in the UK Childhood Cancer Study (UKCCS), a national, population-based case-control study. Analyses included 3500 children with cancer (cases) of whom 1637 were diagnosed with leukaemia, 114 with Hodgkin's disease, 228 with non-Hodgkin's lymphoma and 1521 with other cancer and 6964 controls. 62% cases and 64% controls were reported to have ever been breastfed. There was weak evidence, of borderline statistical significance, that having been breastfed was associated with a small reduction in the odds ratios for leukaemia (odds ratio = 0.89, 95% Cl 0.80-1.00, P = 0.06), and for all cancers combined (odds ratio = 0.92, 95% Cl 0.84-1.00, P = 0.05). Combining data from the UKCCS with results from other published studies showed a small reduction in the odds ratios for leukaemia, Hodgkin's disease, non-haematological cancers, and all childhood cancers combined, associated with ever having been breastfed. It is unclear whether the apparent small reduction in the odds ratio for these various types of childhood cancer is a generalized effect of breastfeeding or whether it reflects some systematic bias in the majority of studies that have investigated the question.

Space-time clustering of childhood lymphatic leukaemias and non-Hodgkin's lymphomas in Sweden

BACKGROUND

The discussion concerning clusters of childhood leukaemia has mainly been focused on their relation to the time and place of diagnosis. Recently some studies have indicated clustering not only at diagnosis, but also around time and place of birth. Space-time clustering at time of birth could be of special interest if the aetiological agent is of infectious origin and the induction of leukaemia either occurs pre- or perinatally or an infection at that time favours a poor subsequent immune response to the agent.

METHODS

To identify possible space-time clustering we have used the close-pair method of Knox. One-thousand-twenty recorded cases (0-14 years) of childhood acute lymphatic leukaemia and 293 cases (0-14 years) of malignant non-Hodgkin's lymphoma from Sweden between 1973-1996 were analysed. The records include date of birth and of diagnosis as well as addresses at birth and at diagnosis.

RESULTS

A significant excess of case-pairs (25 observed, 14.9 expected, p = 0.01) was observed close in date and place of birth in the 4-14 year age group with acute lymphatic leukaemia (ALL). However there was no statistically significant clustering found around time of diagnosis. When the cases of leukaemia and the non-Hodgkin's lymphomas were combined no statistically significant clustering was obtained neither at birth nor at diagnosis.

CONCLUSIONS

This study strengthens the evidence of space-time clustering around the birth date in children whom later developed ALL. This observation is in support of the hypothesis that pre- or perinatal infections can induce a process leading to ALL.

Longer breast-feeding and protection against childhood leukaemia and lymphomas

The role of breast-feeding in protecting against childhood acute leukaemia and lymphomas is uncertain. We investigated this issue in a case-control study comprising 117 patients, aged 2-14 years, with acute lymphocytic leukaemia (ALL), Hodgkin's (HL) and non-Hodgkin's lymphoma (NHL), as well as 117 controls matched for age, sex and ethnicity. Information was collected via a telephone interview of the mothers. The median duration of breast-feeding among patients was significantly shorter than among controls, 7 (range 0-23) and 10 (range 0-20) months, respectively (P<0.0001). Breast-feeding of 0-6 months' duration, when compared with feeding of longer than 6 months, was associated with increased odds ratios (OR) for ALL (OR=2.47, 95% confidence interval (CI) 1.17-5.25), HL (OR=3.75, 95% CI 0.80-18.69), NHL (OR=4.06, 95% CI 0.82-22.59), and overall (OR=2.79, 95% CI 1.54-5.05). In the patient group, there were a significantly higher number of children and people per family, and patients were of a higher birth order than controls. In multivariate analysis, breast-feeding duration continues to be an independent predictor of lymphoid malignancies (P=0.015). In conclusion, breast-feeding lasting longer than 6 months may protect against childhood acute leukaemia and lymphomas.

Parental occupation and other factors and cancer risk in children: I. Study methodology and non-occupational factors

A population-based case-control study of risk factors for childhood cancer was conducted for 593 cases diagnosed over the period 1986-1988 in Moscow children 0 to 14 years of age. Two healthy controls to every case were selected from registers of local pediatric polyclinics by age, gender and residence. The parents of 593 cases and 1181 controls were interviewed face-to-face. Significantly higher odds ratios (OR) were associated with cancer in close relatives [OR 1.6; 95% confidence interval (CI) 1.3-1.9], any pathology associated with pregnancy (OR 2.9; 95% CI 2.4-3.6), including threatened miscarriage (OR 2.1; 95% CI 1.5-3.0), toxemia (OR 2.2; 95% CI 1.8-2.8) and hormone treatment during pregnancy (OR 2.2; 95% CI 1.0-4.5). Pre-term births were significantly associated with brain-cancer risk (6/1; OR 13.3; 95% CI 1.5-301.2). For low birth weight (< or = 2500 g) children born from full-term pregnancy, the OR for all cancers combined was 2.5 (23/22; 95% CI 1.4-4.7) and for leukemias 4.7 (9/4; 95% CI 1.4-16.5). In all, 100 cases and 151 controls had birth weight > or = 4000 g (OR 1.4; 95% CI 1.1-1.9). Risk of nephroblastoma was also significantly related to this factor (11/5; OR 5.1; 95% CI 1.6-16.4). A positive trend of OR with decreasing duration of breastfeeding was significant for all cancer combined (p < 0.05). Significantly higher OR were observed for dermatitis (12/6; OR 4.0; 95% CI 1.4-12.1) and viral hepatitis (40/22; OR 3.8; 95% CI 2.3-6.3) in child medical history.

Breast-feeding and risk of childhood acute leukemia

BACKGROUND

Breast-feeding is well known to have a protective effect against infection in infants. Although the long-term effects of breast-feeding on childhood cancer have not been studied extensively, a protective effect against childhood Hodgkin's disease and lymphoma has been suggested previously from small investigations. In this study, we tested the hypothesis that breast-feeding decreases the risk of childhood acute leukemia.

METHODS

A total of 1744 children with acute lymphoblastic leukemia (ALL) and 1879 matched control subjects, aged 1-14 years, and 456 children with acute myeloid leukemia (AML) and 539 matched control subjects, aged 1-17 years, were included in the analysis. Information regarding breast-feeding was obtained through telephone interviews with mothers. All leukemias combined, histologic type of leukemia (ALL versus AML), immunophenotype of ALL (early pre-B cell, pre-B cell, or T cell), and morphology of AML were assessed separately in the data analysis.

RESULTS

Ever having breast-fed was found to be associated with a 21% reduction in risk of childhood acute leukemias (odds ratio [OR] for all types combined = 0.79; 95% confidence interval [CI] = 0.70-0.91). A reduction in risk was seen separately for AML (OR = 0.77; 95% CI = 0.57-1.03) and ALL (OR = 0.80; 95% CI = 0.69-0.93). The inverse associations were stronger with longer duration of breast-feeding for total ALL and AML; for M0, M1, and M2 morphologic subtypes of AML; and for early pre-B-cell ALL.

CONCLUSION

In this study, breast-feeding was associated with a reduced risk of childhood acute leukemia. If confirmed in additional epidemiologic studies, our findings suggest that future epidemiologic and experimental efforts should be directed at investigating the anti-infective and/or immune-stimulatory or immune-modulating effects of breast-feeding on leukemogenesis in children.

Association of childhood leukaemia with factors related to the immune system

The childhood peak of common acute lymphoblastic leukaemia has been proposed as being a rare response to delayed exposure to a common infection. In this context, factors related to the child's immune system are of special interest. Information on such factors was obtained in a recent German case-control study comprising more than 1000 children with acute leukaemia. Neither being the first-born child, nor a short duration of breastfeeding, indicators of a deficit in viral contacts during infancy or the number of infectious diseases, were significant risk factors. We observed a strong association with fewer routine immunizations with a 3.2-fold increase for those children getting less than four immunizations, but this association could partly be explained by reporting bias. While tonsillectomy or appendectomy increased the risk of leukaemia in our studies, a protective effect of allergies could be seen. In summary, we found only weak support for the delayed exposure hypothesis. To some extent this may be due to the chosen surrogate markers which reflect, rather indirectly, immunological isolation in infancy and delayed exposure to common viruses. However, the significant findings for routine immunizations, tonsillectomy and allergies of the child or its parents merit further investigation.

Insulin-like growth factor-I and binding protein-3 in relation to childhood leukaemia

The aetiology of most cases of childhood leukaemia remains unknown, but several studies have indicated that increased birthweight and height are risk factors for the disease. Since insulin-like growth factor-I (IGF-I) mediates the effect of growth hormone and has been positively associated with prostate cancer, we have evaluated the role of this hormone and its principal binding protein, IGFBP-3, in the aetiology of childhood leukaemia. Incident cases of childhood leukaemia from those recorded by a national network of childhood oncologists were enrolled in our study. Controls were children hospitalised for acute conditions of no more than moderate severity with matching for gender, age and maternal place of residence. Blood measurements of IGF-I and IGFBP-3 were undertaken using commercially available radioimmunoassays. Serum IGF-I values decreased by about 1.7% per month, and the rate of decline was higher, though not significantly so, among cases (2.1% per month) than among controls (1.4%). There was no significant association between IGF-I and the likelihood of childhood leukaemia, but an increment of 1 microg/ml of IGFBP-3 was associated with a substantial and statistically significant reduction of childhood leukaemia by 28% (95% confidence interval 7% to 45%). Because IGFBP-3 is essentially a binding protein, we interpret our findings as indicating that bioavailable IGF-I may play an important role in the aetiology of childhood leukaemia. The much smaller quantities and the inherent instability of IGF-I in the blood in comparison to those of IGFBP-3 are likely to hinder documentation of an underlying positive association of IGF-I with the disease.

The causes of acute leukemia

Although impressive biologic advances have increased understanding of leukemogenesis, we know little about the causes of the acute leukemias. Epidemiologic studies have focused primarily on children. Higher birth weight is associated with an increased risk of childhood acute leukemia. Several theories have been advanced that may account for these observations, and additional biologic studies are needed. Some epidemiologic studies suggest that the acute leukemias in children may have an infectious component. Again, further work, especially in the area of specific causative agents, is necessary. Another area for future epidemiologic study includes investigation of exposure to natural and synthetic DNA topoisomerase II inhibitors. Preliminary evidence suggests that exposure to these agents, which are found in certain foods and medications, may be related to the subsequent development of acute leukemia in infants.

Electrical power lines and childhood leukemia: a study from Greece

Residential proximity to electrical power lines of different voltage in relation to childhood leukemia was investigated through a case-control study undertaken in Greece during 1993-1994. The study comprised 117 incident cases of childhood leukemia and 202 age-, gender- and place-of-residence-matched controls. Four measures of exposure to magnetic fields were developed, using data provided by the Public Power Corporation of Greece: Voltage (V) divided by the distance (d), V/d2, V/d3 and an adaptation of the Wertheimer-Leeper code. Conditional-logistic-regression modeling was used to adjust for potential confounding influences of 18 variables. No significant trends of childhood leukemia risk with increasing exposure levels were noted, nor were there statistically significant elevations of disease risk at the higher exposure levels in each measure of exposure. These results do not support a causal link between residential proximity to electrical high-voltage wires and childhood leukemia risk, but in themselves do not refute a weak empirical association.