Environmental, maternal, and reproductive risk factors for childhood acute lymphoblastic leukemia in Egypt: a case-control study.

BACKGROUND: Acute lymphocytic leukemia (ALL) is the most common pediatric cancer. The exact cause is not known in most cases, but past epidemiological research has suggested a number of potential risk factors. This study evaluated associations between environmental and parental factors and the risk for ALL in Egyptian children to gain insight into risk factors in this developing country. METHODS: We conducted a case-control design from May 2009 to February 2012. Cases were recruited from Children's Cancer Hospital, Egypt (CCHE). Healthy controls were randomly selected from the general population to frequency-match the cumulative group of cases by sex, age groups (<1; 1 - 5; >5 - 10; >10 years) and region of residence (Cairo metropolitan region, Nile Delta region (North), and Upper Egypt (South)). Mothers provided answers to an administered questionnaire about their environmental exposures and health history including those of the father. Odds ratios (ORs) and 95 % confidence intervals (CI) were calculated using logistic regression with adjustment for covariates. RESULTS: Two hundred ninety nine ALL cases and 351 population-based controls frequency-matched for age group, gender and location were recruited. The risk of ALL was increased with the mother's use of medications for ovulation induction (ORadj = 2.5, 95 % CI =1.2 -5.1) and to a lesser extend with her age (ORadj = 1.8, 95 % CI = 1.1 - 2.8, for mothers ≥ 30 years old). Delivering the child by Cesarean section, was also associated with increased risk (ORadj = 2.01, 95 % CI =1.24-2.81). CONCLUSIONS: In Egypt, the risk for childhood ALL appears to be associated with older maternal age, and certain maternal reproductive factors.

Evaluating the Role of Birth Weight and Gestational Age on Acute Lymphoblastic Leukemia Risk Among Those of Hispanic Ethnicity.

High birth weight is an established risk factor for childhood acute lymphoblastic leukemia (ALL), especially in children younger than 5 years of age at diagnosis. The goal of this study was to explore the association between being born large for gestational age and the risk for ALL by race/ethnicity to determine if the role of this risk factor differed by these characteristics. The authors compared birth certificate data of 575 children diagnosed with ALL who were younger than 5 years and included in the Texas Cancer Registry, Texas Department of Health, between the years 1995 and 2003 with 11,379 controls matched by birth year. Stratified odds ratios were calculated for risk of ALL by birth weight for gestational age, categorized in 3 groups, small, appropriate, and large for gestational age (SGA, AGA, and LGA, respectively), for each race/ethnicity group. The risk of developing ALL was higher among Hispanics who were LGA (odds ratio [OR] = 1.90, 95% confidence interval [CI]: 1.34-2.68) compared with LGA non-Hispanic whites (OR = 1.27, 95% CI: 0.87-1.86) after adjusting for infant gender, year of birth, maternal age, birth order, and presence of Down syndrome. However, the difference was not statistically significant. These results suggest that there may be differences in the association between higher growth in utero and risk of childhood ALL among Hispanics versus non-Hispanic whites.

Genetic markers in a multi-ethnic sample for childhood acute lymphoblastic leukemia risk.

Genome-wide association studies have identified multiple risk loci for childhood acute lymphoblastic leukemia (ALL), but mostly in European/White populations, despite Hispanics having a greater risk. We re-examined single nucleotide polymorphisms (SNPs) of known associations with childhood ALL and known human leukocyte antigen (HLA) region lymphoma risk markers in a multi-ethnic population. Significant associations were found in two ARID5B variants (rs7089424 and rs10821936). We replicated a strong risk association in non-Hispanic White males with rs2395185, a protective marker for lymphoma. Another HLA region marker, rs2647012, showed a risk association among Hispanics only, while a strong protective association was found with rs1048456, a follicular lymphoma risk marker. Our study validated this new case-control sample by confirming genetic markers associated with childhood ALL, and yielded new associations with lymphoma markers. Despite positive results, our study did not provide any clues as to why Hispanics have a higher susceptibility to childhood leukemia, suggesting that environmental factors may have a strong contribution.

Examination of HFE associations with childhood leukemia risk and extension to other iron regulatory genes.

Hereditary hemochromatosis (HFE) variants correlating with body iron levels have shown associations with cancer risk, including childhood acute lymphoblastic leukemia (ALL). Using a multi-ethnic sample of cases and controls from Houston, TX, we examined two HFE variants (rs1800562 and rs1799945), one transferrin receptor gene (TFRC) variant (rs3817672) and three additional iron regulatory gene (IRG) variants (SLC11A2 rs422982; TMPRSS6 rs855791 and rs733655) for their associations with childhood ALL. Being positive for either of the HFE variants yielded a modestly elevated odds ratio (OR) for childhood ALL risk in males (1.40, 95% CI=0.83-2.35), which increased to 2.96 (95% CI=1.29-6.80) in the presence of a particular TFRC genotype for rs3817672 (P interaction=0.04). The TFRC genotype also showed an ethnicity-specific association, with increased risk observed in non-Hispanic Whites (OR=2.54, 95% CI=1.05-6.12; P interaction with ethnicity=0.02). The three additional IRG SNPs all showed individual risk associations with childhood ALL in males (OR=1.52-2.60). A polygenic model based on the number of variant alleles in five IRG SNPs revealed a linear increase in risk among males with the increasing number of variants possessed (OR=2.0 per incremental change, 95% CI=1.29-3.12; P=0.002). Our results replicated previous HFE risk associations with childhood ALL in a US population and demonstrated novel associations for IRG SNPs, thereby strengthening the hypothesis that iron excess mediated by genetic variants contributes to childhood ALL risk.

Gender differences in cancer susceptibility: an inadequately addressed issue.

The gender difference in cancer susceptibility is one of the most consistent findings in cancer epidemiology. Hematologic malignancies are generally more common in males and this can be generalized to most other cancers. Similar gender differences in non-malignant diseases including autoimmunity, are attributed to hormonal or behavioral differences. Even in early childhood, however, where these differences would not apply, there are differences in cancer incidence between males and females. In childhood, few cancers are more common in females, but overall, males have higher susceptibility. In Hodgkin lymphoma, the gender ratio reverses toward adolescence. The pattern that autoimmune disorders are more common in females, but cancer and infections in males suggests that the known differences in immunity may be responsible for this dichotomy. Besides immune surveillance, genome surveillance mechanisms also differ in efficiency between males and females. Other obvious differences include hormonal ones and the number of X chromosomes. Some of the differences may even originate from exposures during prenatal development. This review will summarize well-documented examples of gender effect in cancer susceptibility, discuss methodological issues in exploration of gender differences, and present documented or speculated mechanisms. The gender differential in susceptibility can give important clues for the etiology of cancers and should be examined in all genetic and non-genetic association studies.

Multiple sclerosis risk markers in HLA-DRA, HLA-C, and IFNG genes are associated with sex-specific childhood leukemia risk.

Previous epidemiologic studies showed four times increased risk of acute lymphoblastic leukemia (ALL) in children of women with multiple sclerosis (MS). MS shows a risk association with Human leukocyte antigens (HLA)-DRA single nucleotide polymorphism (SNP) rs3135388, which is a proxy marker for DRB1*1501. We examined the relevance of rs3135388 in childhood ALL risk along with two other HLA-DRA SNPs in two case-control groups: 114 cases and 388 controls from South Wales (UK) and 100 Mexican Mestizo cases and 253 controls. We first confirmed the correlation between rs3135388 and DRB1*1501 in HLA-typed reference cell lines. We noted a female-specific risk association in childhood ALL (pooled odds ratio (OR) = 2.6, 95% confidence interval (CI) = 1.5-4.5, Mantel-Haenszel P = 0.0009) similar to the stronger association of DRB1*1501 in females with MS. Examination of an HLA-C 5' flanking region SNP rs9264942, known to correlate with HLA-C expression, showed a protective association in girls (OR = 0.4, 95% CI = 0.2-0.7, Mantel-Haenszel P = 0.0003) similar to the protective HLA-Cw*05 association in MS. In a reference cell line panel, HLA-Cw5 homozygous samples (n = 8) were also homozygous for the minor allele of the SNP. Likewise, the male-specific protective association of interferon-gamma (IFNG) SNP rs2069727 in MS was replicated with the same sex specificity in childhood ALL (OR = 0.6, 95% CI = 0.4-1.0, Mantel-Haenszel P = 0.03). Two other SNPs in superkiller viralicidic activity 2-like and tenascin XB that are markers for systemic lupus erythematosus susceptibility showed female-specific associations but due to linkage disequilibrium with HLA-DRB1*15. Our observations supported the epidemiologic link between MS and childhood ALL and added the sex effect to this connection. It appears that only girls born to mothers with MS may have an increased risk of ALL. Investigating the mechanism of these sex-specific associations may help understand the pathogenesis of MS and ALL.

Examination of genetic polymorphisms in newborns for signatures of sex-specific prenatal selection.

Success rate in human pregnancies is believed to be very low and sex-specific mechanisms may operate in prenatal loss. Assuming a sex-differential in prenatal loss exists, we examined genetic markers in biologically plausible targets in the HLA complex, other immune system-related and iron-regulatory genes in 388 healthy newborns from Wales (UK) using one sex as a control group for the other. Genotyping of 333 single nucleotide polymorphisms (SNPs) from 107 genes was achieved mainly by TaqMan assays. Twenty-two of autosomal SNPs showed frequency differences between 187 male and 201 female newborns either individually or as part of a haplotype. Of these, six markers (RXRB rs2076310, HLA complex haplotype HLA-DQA1 rs1142316-HLA-DRA rs7192-HSPA1B rs1061581, HIST1H1T rs198844, IFNG rs2069727, NKG2D rs10772266 and IRF4 heterozygosity) showed statistically robust differences between male and female newborns and multivariable modeling confirmed their independence. There were fewer males homozygote for combined wildtype genotypes of LIF rs929271, TP53 rs1042522 and MDM2 rs2279744 compared with females [OR = 0.3, 95% confidence interval (CI) = 0.1-0.8; P < 0.01] although these SNPs did not show any association individually. It is unlikely that SNPs have clinical utility as single markers in any trait with complex etiology but polygenic predictive models remain a possibility. If their validity is confirmed in larger studies of different populations and functional mechanisms of these preliminary associations are elucidated, these markers from the HLA complex, NKG2D region and cytokines may cumulatively have sufficient predictive value for susceptibility to prenatal selection in each sex.

An extensive analysis of the hereditary hemochromatosis gene HFE and neighboring histone genes: associations with childhood leukemia.

The most common mutation of the HFE gene C282Y has shown a risk association with childhood acute lymphoblastic leukemia (ALL) in Welsh and Scottish case-control studies. This finding has not been replicated outside Britain. Here, we present a thorough analysis of the HFE gene in a panel of HLA homozygous reference cell lines and in the original population sample from South Wales (117 childhood ALL cases and 414 newborn controls). The 21 of 24 variants analyzed were from the HFE gene region extending 52 kb from the histone gene HIST1H1C to HIST1H1T. We identified the single-nucleotide polymorphism (SNP) rs807212 as a tagging SNP for the most common HFE region haplotype, which contains wild-type alleles of all HFE variants examined. This intergenic SNP rs807212 yielded a strong male-specific protective association (per allele OR = 0.38, 95% CI = 0.22-0.64, P (trend) = 0.0002; P = 0.48 in females), which accounted for the original C282Y risk association. In the HapMap project data, rs807212 was in strong linkage disequilibrium with 25 other SNPs spanning 151 kb around HFE. Minor alleles of these 26 SNPs characterized the most common haplotype for the HFE region, which lacked all disease-associated HFE variants. The HapMap data suggested positive selection in this region even in populations where the HFE C282Y mutation is absent. These results have implications for the sex-specific associations observed in this region and suggest the inclusion of rs807212 in future studies of the HFE gene and the extended HLA class I region.

HLA complex-linked heat shock protein genes and childhood acute lymphoblastic leukemia susceptibility.

Three heat shock protein 70 (HSP70) genes, HSPA1L, HSPA1A, and HSPA1B, are located within the human leukocyte antigen (HLA) class III region. HSPs act as stress signals and regulate natural killer cell response to cancer. HSP70 gene polymorphisms show disease associations partly due to their linkage disequilibrium with HLA alleles. To systematically evaluate their associations with childhood acute lymphoblastic leukemia (ALL), we examined the three functional single nucleotide polymorphisms (SNPs) rs2227956 (T493M) in HSPA1L, rs1043618 in HSPA1A 5'UTR, and rs1061581 (Q351Q) in HSPA1B by TaqMan assays or polymerase chain reaction-restriction fragment length polymorphism in 114 ALL cases and 414 controls from Wales (UK), in 100 Mexican Mestizo ALL cases and 253 controls belonging to the same ethnic group, and in a panel of 82 HLA-typed reference cell line samples. Homozygosity for HSPA1B rs1061581 minor allele G was associated with protection (odds ratio (OR) = 0.37, 95% confidence interval (CI) = 0.16-0.78; P = 0.007) with gene-dosage effect (additive model) reaching significance (P = 0.0001) in the Welsh case-control group. This association was replicated in the second case-control group from Mexico (OR (recessive model) = 0.49, 95% CI = 0.24-0.96; P = 0.03), and the pooled analysis yielded a strong association (Mantel-Haenszel OR = 0.43, 95% CI = 0.27-0.69, P = 0.0004). The association was stronger in males in each group and in the pooled analysis. A three-SNP haplotype including the major allele A of rs1061581 showed a highly significant increase in Welsh cases compared with respective controls (6.7% vs 1.8%; P = 0.0003) due to the difference between male cases and controls. The protective allele of rs1061581 occurred more frequently on the HLA-DRB3 haplotypes (especially DRB1*03) in the cell line panel, but the HSPA1B association was independent from the HLA-DRB4 association previously detected in the same case-control group from Wales (adjusted P = 0.001). Given the cancer promoting roles played by HSPs intracellularly as well as roles in immune surveillance when expressed on the cell surface and the known correlations between expression levels and the HSP polymorphisms, these results are likely to indicate a primary association and warrant detailed assessment in childhood ALL development.

An intronic polymorphism of IRF4 gene influences gene transcription in vitro and shows a risk association with childhood acute lymphoblastic leukemia in males.

The interferon regulatory factor (IRF) family of DNA-binding proteins regulates expression of interferon-inducible genes with roles in the immune response and carcinogenesis. IRF4 is involved in the differentiation of B and T cells and is overexpressed in B-cell malignancies as a result of c-REL (NF-kappaB) hyperactivation. IRF4 polymorphisms are associated with susceptibility to chronic lymphoid leukemia (CLL) and non-Hodgkin lymphoma (NHL). We examined 13 IRF4 SNPs in 114 cases of childhood acute lymphoblastic leukemia (ALL) and 388 newborn controls from Wales (U.K.) using TaqMan assays. IRF4 intron 4 SNP rs12203592 showed a male-specific risk association (OR=4.4, 95% CI=1.5 to 12.6, P=0.007). Functional consequences of the C>T substitution at this SNP were assessed by cell-based reporter assays using three different cell lines. We found a repressive effect of the rs12203592 wildtype allele C on IRF4 promoter activity (P<0.001) but no repression by the variant allele in any cell line tested. Thus, homozygosity for the rs12203592 variant allele would result in increased IRF4 expression. This increase would be compounded by high levels of NF-kappaB activity in males due to the absence of estrogen. IRF4 differs from other IRFs in its anti-interferon activity which interferes with immune surveillance. We propose that a detailed study of IRF4 can provide information on the mechanism of the sex effect and the role of immune surveillance in childhood ALL development.

TP53 R72P and MDM2 SNP309 polymorphisms in modification of childhood acute lymphoblastic leukemia susceptibility.

Genomic and immunologic surveillance mechanisms are crucial in protection from cancer. The tumor suppressor protein p53, encoded by TP53, is a major regulator of genome surveillance. Among the natural sequence variants of TP53, rs1042522 (R72P) modifies the risk for solid tumors. To investigate its relevance in childhood acute lymphoblastic leukemia (ALL) susceptibility, we genotyped 114 cases and 414 newborn controls from Wales (UK) for polymorphisms in TP53 (R72P), its negative regulator MDM2 (single-nucleotide polymorphism SNP309, rs2279744), and selected HLA complex genes whose products interact with TP53. TP53 R72P showed a risk association with gene dosage effect (P=0.002) resulting in a strong association of homozygous genotype (OR=2.9, 95% CI=1.5-5.6) and no sex effect. SNP309 did not show any association with primary susceptibility to childhood ALL, even after stratification by sex. However, females with SNP309 minor allele had earlier onset of childhood ALL (median age at diagnosis was 36 months in females, but 60 months in males; P=0.002). The HLA complex genes did not show any statistically significant interaction with R72P. We have therefore identified TP53 R72P as a possible risk modifier for childhood ALL and the association of MDM2 with age at onset with sex effect suggests prenatal hormonal programming of childhood ALL susceptibility.

Hereditary hemochromatosis gene (HFE) variants are associated with birth weight and childhood leukemia risk.

BACKGROUND: Our original studies reported an association between the iron-metabolism gene HFE and risk of childhood acute lymphoblastic leukemia (ALL), and a birth weight association in ALL. Through its effect on cell proliferation, iron is involved in both fetal development and cancer. We hypothesize that HFE links higher infant birth weight with leukemia risk and that maternal HFE genotype modifies this association. PROCEDURE: Nine hundred ninety-five infants and their mothers from the North Cumbria Community Genetics Project, and 163 incident childhood ALL cases from the Newcastle Haematology Biobank were genotyped for HFE, HAMP, TFRC variants and 21 genomic control loci. Cord blood iron levels were measured in 217 control infants. RESULTS: Three HFE variants showed correlations with birth weight with a gene-dosage relationship in males (gender effect). The association was stronger in homozygotes for TFRC S142G and when the mother was positive for any HFE variant (maternal effect). The genotypes expected to increase fetal iron levels correlated with birth weight in males and their association with ALL was stronger in females who, we postulate, could not offset iron excess by increasing their weight. CONCLUSIONS: Certain materno-fetal genotype combinations that increase fetal iron exposure showed associations with higher birth weight in males and somewhat higher ALL risk in females. Gender-specific use of iron during fetal growth may lead to this dichotomy in birth weight change. Only the materno-fetal genotype combinations that increase iron levels most extremely correlated with birth weight and ALL risk in males.

Geographical analysis of thyroid cancer in young people from northern England: evidence for a sustained excess in females in Cumbria.

A previous study found a thyroid cancer excess in Cumbria following the Chernobyl explosion, but did not analyse sex-specific effects. This study examines sex differences in the incidence of thyroid cancer. Ninety-five primary thyroid carcinomas (69 females, 26 males) diagnosed in those aged 0-24 during 1968-2005 were identified from the Northern Region Young Persons' Malignant Disease Registry. Age-standardised incidence rates (ASRs), rate ratios (RRs) and 95% confidence intervals (CIs) were calculated. For males, the ASR was 0.6 per million person-years during the pre-Chernobyl period (1968-1986), and was 1.8 per million person-years during the post-Chernobyl period (1987-2005). For females, the ASR was 2.4 pre-Chernobyl and was 3.9 post-Chernobyl. The previously noted excess in Cumbria was entirely confined to females (Cumbrian females: RR for post-Chernobyl compared with pre-Chernobyl=10.8; 95% CI: 1.4-85.3). These findings may be consistent with sex-specific differences in susceptibility to an environmental exposure, such as fallout from the Chernobyl nuclear accident.

Sex-specific incidence and temporal trends in solid tumours in young people from Northern England, 1968-2005.

BACKGROUND: This study examined sex-specific patterns and temporal trends in the incidence of solid tumours in the Northern Region of England from 1968 to 2005. This updates earlier analyses from the region where sex was not considered in depth. Sex-specific analyses were carried out to determine whether sex differences might provide clues to aetiology. METHODS: Details of 3576 cases, aged 0-24 years, were obtained from a specialist population-based cancer registry. There were 1843 males (886 aged 0-14 years and 957 aged 15-24 years) and 1733 females (791 aged 0-14 years and 942 aged 15-24 years). Age-standardized incidence rates (per million population) were calculated. Linear regression was used to analyze temporal trends in incidence and annual percentage changes were estimated. Analyses were stratified by sex and by age-group. RESULTS: There were marked differences in incidence patterns and trends between males and females and also between age-groups. For males central nervous system (CNS) tumours formed the largest proportion of under-15 cases and germ cell tumours was the largest group in the 15-24's, whilst for females CNS tumours dominated in the under-15's and carcinomas in the older group. For 0-14 year olds there were male-specific increases in the incidence of rhabdomyosarcoma (2.4% per annum; 95% CI: 0.2%-4.5%) and non-melanotic skin cancer (9.6%; 95% CI: 0.0%-19.2%) and female-specific increases for sympathetic nervous system tumours (2.2%; 95% CI: 0.4%-3.9%), gonadal germ cell tumours (8.6%; 95% CI: 4.3%-12.9%) and non-gonadal germ cell tumours (5.4%; 95% CI: 2.8%-7.9%). For 15-24 year olds, there were male-specific increases in gonadal germ cell tumours (1.9%; 95% CI: 0.3%-3.4%), non-gonadal germ cell tumours (4.4%; 95% CI: 1.1%-7.7%) and non-melanotic skin cancer (4.7%; 95% CI: 0.5%-8.9%) and female-specific increases for osteosarcoma (3.5%; 95% CI: 0.5%-6.5%), thyroid cancer (2.8%; 95% CI: 0.1%-5.6%) and melanoma (4.6%; 95% CI: 2.2%-7.1%). CONCLUSION: This study has highlighted notable differences between the sexes in incidence patterns and trends for solid tumours. Some of these sex-specific differences could have been obscured if males and females had been analysed together. Furthermore, they suggest aetiological differences or differential susceptibility to environmental factors between males and females.

Role of natural killer cells and killer immunoglobulin-like receptor polymorphisms: association of HLA and KIRs.

Natural killer cells play an important role in innate immunity. They act against infected and transformed cells as part of the immune surveillance process. Their interactions with the human leukocyte antigens (HLAs) create a situation where they may act against donor hematopoietic cells following stem cell transplantation. Both killer immunoglobulin-like receptors (KIRs) and HLA types of donor and recipient are relevant in the generation of graft-vs-leukemia or graft-vs-host reactions. This chapter reviews the current knowledge on the involvement of natural killer cells in the events following hematopoietic stem cell transplantation, the structure of the genetic complex encoding the KIRs and provides a PCR-based genotyping scheme for KIR genes.

Examination of gender effect in birth weight and miscarriage associations with childhood cancer (United Kingdom).

BACKGROUND: Higher birth weight and maternal history of miscarriage has been associated with an increased risk of childhood leukemia. The possibility that this association may be sex-specific has not been explored in detail in previous studies. METHODS: In a retrospective case-control study, 732 childhood (< or =14 years) cancer cases from a population-based Registry in Northern England whose hospital birth records could be accessed and 3,723 controls matched for date and hospital of birth to the cases were compared. We examined birth weight for sex-specific associations with childhood cancer. Conditional logistic regression analysis was used for statistical evaluation of associations. RESULTS: In acute lymphoblastic leukemia (ALL) (225 cases and 1,163 matched controls), birth weight and sex showed a strong interaction (P = 0.003). In boys with ALL, but not in girls, there was a nonlinear association with birth weight (P for trend = 0.008; OR = 3.05 for the highest quintile compared to the second lowest quintile, 95% CI = 1.40-6.64; P = 0.005). When birth weights were adjusted using UK standards for gestational age and sex, the risk associations were similar in statistical significance and magnitude. Maternal history of miscarriage showed an association with all cancers and individually with ALL. The miscarriage association with ALL was statistically significant in boys only (OR = 1.91, 95% CI = 1.07-3.42; P = 0.03). A multivariable model for ALL containing other examined maternal and reproductive variables confirmed the independence of the birth weight and miscarriage associations. There was no birth weight or miscarriage associations in other cancers. CONCLUSIONS: This study confirmed the risk associations with birth weight and miscarriages in childhood ALL. Statistically significant association of size at birth suggested marked differences in etiology between girls and boys.

Paternal occupational exposure to electro-magnetic fields as a risk factor for cancer in children and young adults: a case-control study from the North of England.

BACKGROUND: Numerous studies have implied that paternal occupational exposures, in particular electromagnetic fields (EMF) and ionizing radiation, may be involved in the etiology of childhood cancers. We investigated whether an association exists between paternal occupations at birth involving such exposures and cancer risk in offspring, using data from the Northern Region Young Persons' Malignant Disease Registry (NRYPMDR). PROCEDURE: Cases (n=4,723) were matched, on sex and year of birth, to controls from two independent sources: (i) all other patients from the NRYPMDR with a different cancer, (ii) 100 cancer-free individuals per case from the Cumbrian Births Database. An occupational exposure matrix was used to assign individuals to exposure groups. RESULTS: There was an increased risk of leukemia among the offspring of men employed in occupations likely to be associated with EMF or radiation exposures (OR 1.31, 95% CI 1.02-1.69), particularly in males aged less than 6 years (OR 1.81, 95% 1.19-2.75). No significant association was seen in females. Increased risks were also seen for chondrosarcoma (OR 8.7, 95% CI 1.55-49.4) and renal carcinoma (OR 6.75, 95% CI 1.73-26.0). These associations were consistent between control groups and remained after adjustment for socio-economic status. CONCLUSIONS: This large case-control study identified a significantly increased risk of leukemia among the offspring of men likely to have been occupationally exposed to EMF, with differing associations between males and females. Increased risks of chondrosarcoma and renal carcinoma were also seen, although based on smaller numbers. Further detailed investigations in this area are required to understand this association.