Allergy and risk of childhood leukaemia: results from the UKCCS

We investigated the relationship between childhood leukaemia and preceding history of allergy. A nationwide case-control study of childhood cancers was conducted in the United Kingdom with population-based sampling of cases (n = 839) and controls (n = 1,337), matched on age, sex and region of residence. Information about clinically diagnosed allergies was obtained from primary care records. More than a third of subjects had at least one allergy diagnosed prior to leukaemia diagnosis (cases) or pseudo-diagnosis (controls). For both total acute lymphoblastic leukaemia (ALL) and common-ALL/precursor B-cell ALL (c-ALL), a history of eczema was associated with a 30% significant reduction in risk: the odds ratios (OR) and 95% confidence intervals (CI) were 0.70 (0.51-0.97) and 0.68 (0.48-0.98), respectively. Similar associations were observed for hayfever (OR = 0.47; 95% CI: 0.26-0.85 and OR = 0.62; 95% CI: 0.33-1.16 for ALL and c-ALL, respectively). No such patterns were seen either for asthma and ALL, or for any allergy and acute myeloid leukaemia. A comparative analysis of primary care records with parents recall of allergy revealed only moderate agreement with contemporaneous clinical diagnoses for both cases and controls--confirming the unreliability of parental report at interview. Our finding of a reciprocal relationship between allergy and ALL in children is compatible with the hypothesis that a dysregulated immune response is a critical determinant of childhood ALL.     

Seasonal variations in the onset of childhood leukaemia and lymphoma.

Infection has long been suspected as a possible factor in the aetiology of leukaemia and lymphoma. If seasonal variation in the onset of disease could be shown in any of the diagnostic subgroups of leukaemia or lymphoma, this would provide supportive evidence of an aetiology linked to exposure to infection. All cases in the Manchester Children''s Tumour Registry (aged 0-14 years at diagnosis) with acute lymphoblastic leukaemia (ALL), acute non-lymphocytic leukaemia (ANLL), Hodgkin''s disease (HD) or non-Hodgkin lymphoma (NHL) between 1 January 1954 and 31 December 1996 were included in an analysis of seasonal variation in the month of first symptom and the month of diagnosis. Cases of common acute lymphoblastic leukaemia (c-ALL) diagnosed from 1979 onwards were also analysed separately. The groups considered for analysis were: all cases of ALL (n = 1070), ALL diagnosed between 18 and 95 months of age (n = 730), ALL diagnosed over 95 months of age (n = 266), c-ALL (n = 309), ANLL (n = 244), all infant acute leukaemias (ALL and ANLL under 18 months; n = 107), HD (n = 166) and NHL (n = 189). Using the Edwards method, both c-ALL and HD demonstrated significant seasonal variation (P = 0.037 and 0.001 respectively) in date of first symptom, with peaks occurring in November and December respectively. Using this method, no indication of seasonal variation was found in the other diagnostic groups for date of first symptom or in any of the diagnostic groups for date of diagnosis. For comparison with a previous study, a further analysis based on date of diagnosis for all ALL cases, using summer-winter ratios, showed a significant summer excess. These results provide supportive evidence for an infectious aetiology for c-ALL and HD, and possibly for all ALL, which warrants further investigation.     

Case–control study of paternal occupation and childhood leukaemia in Great Britain, 1962–2006

Background:

Paternal occupational exposures have been proposed as a risk factor for childhood leukaemia. This study investigates possible associations between paternal occupational exposure and childhood leukaemia in Great Britain.

Methods:

The National Registry of Childhood Tumours provided all cases of childhood leukaemia born and diagnosed in Great Britain between 1962 and 2006. Controls were matched on sex, period of birth and birth registration subdistrict. Fathers'' occupations were assigned to 1 or more of 33 exposure groups. Social class was derived from father''s occupation at the time of the child''s birth.

Results:

A total of 16 764 cases of childhood leukaemia were ascertained. One exposure group, paternal social contact, was associated with total childhood leukaemia (odds ratio 1.14, 1.05–1.23); this association remained significant when adjusted for social class. The subtypes lymphoid leukaemia (LL) and acute myeloid leukaemia showed increased risk with paternal exposure to social contact before adjustment for social class. Risk of other leukaemias was significantly increased by exposure to electromagnetic fields, persisting after adjustment for social class. For total leukaemia, the risks for exposure to lead and exhaust fumes were significantly <1. Occupationally derived social class was associated with risk of LL, with the risk being increased in the higher social classes.

Conclusion:

Our results showed some support for a positive association between childhood leukaemia risk and paternal occupation involving social contact. Additionally, LL risk increased with higher paternal occupational 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.     

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.     

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.     

Parental occupation and childhood astrocytoma: results of a case-control study.

Parental occupations were investigated as possible risk factors for astrocytoma, the most frequently occurring brain tumor in children. A case-control study of 163 pairs was performed. Cases under 15 years of age at diagnosis in 1980-1986 were identified through the tumor registries of eight hospitals in Pennsylvania, New Jersey, and Delaware. Controls were selected by random-digit dialing and were matched to cases on age, race, and telephone area code. Occupations before the child's conception, during the pregnancy, and after the child's birth were studied separately. We did not observe any strong associations. Significantly more fathers of cases were electrical or electronic repairmen, a subgroup of an occupational category previously associated with increased risk. An excess of case mothers employed as nurses was observed, which was significant for mothers of children diagnosed before 5 years of age. Elevated although not significant odds ratios were observed for some white collar and professional occupations in case parents; for paternal exposure to paint and paternal occupation in the paper and pulp mill industry, both in the period after the child's birth; and for maternal occupation as a hairdresser. The lack of strong associations may have resulted from low statistical power for some job groupings. Our study, unlike previous studies, focused on a single type of brain tumor: childhood astrocytoma. Thus our results suggest that some parental occupations associated with childhood brain tumors in previous studies may not be risk factors for childhood astrocytoma.     

Childhood Cancer and Social Contact: the Role of Paternal Occupation (United Kingdom)*

Objective: To investigate the relationship between childhood cancer (particularly leukaemia) and paternal occupational social contact (a proxy for potential exposure to infections) using the UK Childhood Cancer Study. Methods: Using a national population-based case–control study, self-reported occupational data from fathers of 3596 children diagnosed with cancer between 1991 and 1996 under 15 years of age (cases) and fathers of 7011 children without cancer (controls) were analysed. Associations were assessed using odds ratios (OR) calculated by time of exposure (birth, diagnosis), diagnostic group (all cancers, leukaemia, acute lymphoblastic leukaemia (ALL), central nervous system tumours, other cancers), level of occupational social contact (high, medium, low), urban–rural status at diagnosis and occupational title. Results: From 371 occupations, 75 (20%) were classified as having high levels of occupational social contact, 31 (8%) as medium and the remaining 265 (71%) as low. No associations were apparent for fathers’ occupational social contact overall, for any time period or diagnostic group. OR for leukaemia and high levels of paternal occupational social contact at birth and diagnosis being 1.02 (95% confidence interval (CI) = 0.88–1.18) and 0.91 (95% CI = 0.79–1.06), respectively. Analyses by urban–rural status at diagnosis and by occupational title revealed no notable associations. Conclusions: The analyses of paternal occupational histories do not support the suggested association between high levels of paternal occupational social contact and an increased risk of childhood leukaemia. However, the role of participation bias should not be discounted. See Appendix 1 for Regional Investigators and Management Committee. Financial support: Leukaemia Research Fund, UK.     

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.     

Patterns of infection and day care utilization and risk of childhood acute lymphoblastic leukaemia

To investigate if decreased exposure to common childhood infections is associated with risk of childhood acute lymphoblastic leukaemia (ALL) we conducted a case-control study of 1842 newly diagnosed and immunophenotypically defined cases of ALL under age 15, and 1986 matched controls in the US. Data regarding day care, sibship size and common childhood infections were obtained through parental interviews. Data were analysed stratified by leukaemia lineage and separately for 'common' childhood ALL (age 2-5 years, CD19, CD10-positive). Neither attendance at day care nor time at day care was associated with risk of ALL overall or 'common' ALL. Ear infections during infancy were less common among cases, with odds ratios of 0.86, 0.83, 0.71 and 0.69 for 1, 2-4, 5+ episodes, and continuous infections respectively (trend P = 0.026). No effect of sibship size or birth interval was seen. With one exception (ear infections), these data do not support the hypothesis that a decrease in the occurrence of common childhood infection increases risk of ALL.     

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.     

Exposure to professional pest control treatments and the risk of childhood acute lymphoblastic leukemia

Previous studies suggest that exposure to pesticides increases the risk of childhood acute lymphoblastic leukemia (ALL). The aim of this analysis was to investigate whether professional pest treatments in or around the home before birth or during childhood increased the risk of childhood ALL. Data from 388 cases and 870 frequency-matched controls were analyzed using unconditional logistic regression, adjusting for study matching variables and potential confounders, to calculate odds ratios (ORs). A meta-analysis of our findings with the published findings of previous studies was also conducted. The ORs for any professional pest control treatments were 1.19 (95% CI 0.83, 1.69) in the year before pregnancy, 1.30 (95% CI 0.86, 1.97) during pregnancy and 1.24 (95% CI 0.93, 1.65) for those done after the child's birth. The ORs for exposure after birth were highest when it occurred between the ages of two and three years. ORs were elevated for termite treatments before birth. ORs were higher for pre-B than T cell ALL and for t(12;21) (ETV6-Runx-1) than other cytogenetic sub-types. The pooled OR from a meta-analysis of our study with three previous studies of professional pest control treatments during pregnancy was 1.37 (95% CI 1.00, 1.88). Our results, and those of our meta-analysis, provide some evidence of a modestly increased risk of ALL for professional pest control treatments done during the index pregnancy and possibly in the child's early years. The analysis of pooled data from international collaborations may provide more certainty regarding these potentially important associations.     

Clustering of childhood leukaemia in Hong Kong: association with the childhood peak and common acute lymphoblastic leukaemia and with population mixing.

Incidence data of childhood leukaemia (CL) in Hong Kong (1984-90) have been analysed for evidence of variation between small areas. All cases (n=261) were classified by morphological cell type, with the majority (n=205) being acute lymphoblastic leukaemia (ALL), and haematological review has permitted immunophenotypic classification for 73% of these. The data have been examined for evidence of spatial clustering within small census areas (TPUs) and for association with population mixing, with attention focused on those subgroups (especially the childhood peak of ALL--taken here to be diagnoses in children from 24 months up to the seventh birthday--and common ALL) which, it has been hypothesized, may be caused by unusual patterns of exposure and response to common infections. For the whole of Hong Kong, there was evidence of spatial clustering of ALL at ages 0-4 years (P = 0.09) and in the childhood peak (P<0.05). When these analyses were restricted to TPUs where extreme population mixing may have occurred, overall incidence was elevated and significant evidence of clustering was found for ALL (P<0.007) at these ages and for the common ALL in the childhood peak (P = 0.032). Replication of the analyses for subsets of leukaemia that were not dominated by the childhood peak of ALL found no evidence of clustering. This is the first investigation of an association between population mixing and childhood leukaemia in Asia and the first to include clustering and to consider particular subsets. The results are supportive of the ''infectious'' aetiology hypothesis for subsets of childhood leukaemia, specifically common ALL in the childhood peak.     

Risk of Acute Lymphoblastic Leukemia: Results of a Case-Control Study

Background: Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. Differentenvironmental factors might be effective in the occurrence of this malignancy during childhood. The aim of this studywas to find environmental risk factors in childhood ALL in Hamadan, Iran. Methods: This case-control study wasdone in 2015-2018 on 125 children younger than 15 years of age suffering from ALL. Patients were matched with130 controls with respect to age, gender, and residence location. The identification of risk factors for ALL was soughtbased on the comparison of studied variables between case and control individuals. Results: A statistically significantincreased risk for ALL was found with regard to type of delivery (OR: 0.43, 95% CI: 0.20 - 0.92, p˂0.02), childcare(OR: 4.58, 95% CI: 0.95 - 22.20, p˂0.04), birth weight (OR: 1.44, 95% CI: 1.53 - 2.21, p˂0.006), father’s educationlevel (OR: 2.67, 95% CI: 1.10 - 6.45, p˂0.02), and father’s job (OR: 0.2 95% CI: 0.08 - 0.51, p˂0.001). Also observedwere increased odds for ALL regarding male gender, mother’s high education level, mother’s freelance job, and mediumor high family income. No association with ALL incidence was observed for age, gender, breastfeeding, mother’s ageat pregnancy, malignancy in first- or second-degree relatives, or mother’s use of hair dye during pregnancy (p> 0.05).Conclusion: This study showed that father’s education level, father’s job, delivery type, birth weight, and childcarecan play a role in the incidence of childhood ALL.     

Parental cigarette smoking and the risk of acute leukemia in children

BACKGROUND: Studies of the relation between parental smoking and childhood leukemia have produced inconsistent results. In the largest case-control studies of childhood acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) conducted to date, the authors evaluated leukemia risk relative to parental self-report of cigarette smoking. METHODS: In telephone interviews in which a structured questionnaire was used, parents of 1842 ALL patients, 517 AML patients, and their matched controls were asked about their cigarette smoking habits before, during, and after the pregnancy with the index child. Risk of leukemia was examined by histologic type, age of the child at diagnosis, immunophenotype (for ALL), and French-American-British morphology group (for AML). RESULTS: The risk of ALL was not associated with the father's ever having smoked (odds ratio [OR] = 1.04, 95% confidence interval [CI] 0.90-1.20) or the mother's ever having smoked (OR = 1.04, 95% CI 0.91-1.19). Similarly, no significant risk of AML was observed for paternal (OR = 0.88, 95% CI 0.67-1.16) or maternal smoking (OR = 0.95, 95% CI 0.74-1.22). The relative risk of leukemia was not significantly different from the null for parental smoking in any time period during or around the index pregnancy, nor was it related to the number of cigarettes, the number of years of smoking, or the number of pack-years. A small number of sporadic, statistically significant associations were found, but overall there appeared to be no association between parental cigarette smoking and ALL or AML, or any subgroup of leukemia. CONCLUSIONS: Parental smoking while pregnant or exposure to cigarette smoke shortly after birth is unlikely to contribute substantially to the risk of childhood leukemia in North America.     

Parental occupational exposure to pesticides,animals and organic dust and risk of childhood leukemia and central nervous system tumors: Findings from the International Childhood Cancer Cohort Consortium (I4C)

Parental occupational exposures to pesticides, animals and organic dust have been associated with an increased risk of childhood cancer based mostly on case–control studies. We prospectively evaluated parental occupational exposures and risk of childhood leukemia and central nervous system (CNS) tumors in the International Childhood Cancer Cohort Consortium. We pooled data on 329,658 participants from birth cohorts in five countries (Australia, Denmark, Israel, Norway and United Kingdom). Parental occupational exposures during pregnancy were estimated by linking International Standard Classification of Occupations-1988 job codes to the ALOHA+ job exposure matrix. Risk of childhood (<15 years) acute lymphoblastic leukemia (ALL; n = 129), acute myeloid leukemia (AML; n = 31) and CNS tumors (n = 158) was estimated using Cox proportional hazards models to generate hazard ratios (HR) and 95% confidence intervals (CI). Paternal exposures to pesticides and animals were associated with increased risk of childhood AML (herbicides HR = 3.22, 95% CI = 0.97–10.68; insecticides HR = 2.86, 95% CI = 0.99–8.23; animals HR = 3.89, 95% CI = 1.18–12.90), but not ALL or CNS tumors. Paternal exposure to organic dust was positively associated with AML (HR = 2.38 95% CI = 1.12–5.07), inversely associated with ALL (HR = 0.55, 95% CI = 0.31–0.99) and not associated with CNS tumors. Low exposure prevalence precluded evaluation of maternal pesticide and animal exposures; we observed no significant associations with organic dust exposure. This first prospective analysis of pooled birth cohorts and parental occupational exposures provides evidence for paternal agricultural exposures as childhood AML risk factors. The different risks for childhood ALL associated with maternal and paternal organic dust exposures should be investigated further.     

Is there a folate‐related gene‐environment interaction in the etiology of childhood acute lymphoblastic leukemia?

Acute lymphoblastic leukaemia (ALL) is the commonest childhood cancer in developed countries. Little is known about its causes, although its early age at diagnosis has focused interest on maternal and perinatal factors. We have previously observed a protective effect of maternal folate supplementation during pregnancy against ALL, and a number of studies have reported protective effects of some common polymorphisms of the methylenetetrahydrofolate reductase (MTHFR) gene. One study has suggested that the effect of MTHFR polymorphisms on risk of ALL may depend on folate status. This study aimed to look for evidence of an interaction between maternal folate supplementation and child's genotype among the cases from our previous study. Bone marrow specimens from 82 of 83 case children were available. DNA was extracted and genotyped for MTHFR C677T and A1298C using standard techniques. We used a case-only analysis to estimate the case-only odds ratio (COR) for MTHFR genotype and folate supplementation in association with ALL. None of the CORs indicated a significant departure from a multiplicative model. Adjustment for sex, age or genotype at the other locus had little effect on the results. Other studies of this gene and environment interaction in ALL and other cancers have produced contradictory results, perhaps because of varying definitions of folate exposure. Further research into the interaction of folate intake and genotype in causing ALL and other cancers is needed. We are specifically studying it in an Australian national case-control study of genetic and environmental causes of ALL.     

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.     

Paternal smoking, genetic polymorphisms in CYP1A1 and childhood leukemia risk

We conducted a case-control study to evaluate the association between paternal smoking and childhood leukemia and to evaluate potential modification by polymorphisms in CYP1A1. Histologically confirmed childhood leukemia cases (n=164) and non-cancer controls (n=164) were recruited from three teaching hospitals in Seoul, Korea. Five single nucleotide polymorphisms in CYP1A1 (-17961T>C, -9893G>A, I462V, 1188C>T (*2A), and 11599C>G) were genotyped and haplotypes were estimated by the expectation-maximization method. We also conducted a meta-analysis of 12 studies that have reported the association between paternal smoking and childhood leukemia risk. Paternal smoking at home was associated with all leukemias (OR=1.8, 95% CI=1.1-2.8) and acute lymphoblastic leukemia (ALL) (2.0, 1.2-3.4). An increasing trend in risk was observed for pack-years smoked after birth (P(trend)=0.06 and 0.02, respectively) and the number of smokers in the home during the child's life (P(trend)=0.05 and 0.03, respectively). Among those without the CGACC haplotype, ALL risk was significantly increased by the father's smoking at home (2.8, 1.5-5.3) and the presence of at least one smoker in the home (2.3, 1.2-4.4), and the test for interaction was significant (P(interaction)=0.03 and 0.02, respectively). The meta-analysis showed that overall paternal smoking (1.13, 1.04-1.24) and smoking before the pregnancy of the child (1.12, 1.04-1.21) were significantly associated with childhood leukemia risk. Our results suggest that paternal smoking is a risk factor for childhood leukemia and the effect may be modified by CYP1A1 genotype.     

Risk of childhood acute lymphoblastic leukaemia following parental occupational exposure to extremely low frequency electromagnetic fields

Background:

Earlier studies have reported moderate increases in the risk of acute lymphoblastic leukaemia (ALL) among children whose mothers have been occupationally exposed to extremely low frequency (ELF) electromagnetic fields. Other studies examining parental occupational exposure to ELF and ALL have reported mixed results.

Methods:

In an Australian case–control study of ALL in children aged <15 years, parents were asked about tasks they undertook in each job. Exposure variables were created for any occupational exposure before the birth of the child, in jobs 2 years before birth, in jobs 1 year before birth and up to 1 year after birth.

Results:

In all, 379 case and 854 control mothers and 328 case and 748 control fathers completed an occupational history. Exposure to ELF in all time periods was similar in case and control mothers. There was no difference in exposure between case and control fathers. There was no association between maternal (odds ratio (OR)=0.96; 95% CI=0.74–1.25) or paternal (OR=0.78; 95% CI=0.56–1.09) exposure to ELF any time before the birth and risk of childhood ALL.

Conclusion:

We did not find an increased risk of ALL in offspring of parents with occupational exposure to ELF.