Community lifestyle characteristics and risk of acute lymphoblastic leukaemia in children

Epidemiological evidence for an infective basis in childhood leukaemia

An infective basis for childhood leukaemia is not a new suspicion (Kellett, 1937). The failure of microbiologists to identify any specific agent and of epidemiologists to demonstrate marked space-time clustering of the disease (Smith, 1982) have been discouraging, but neither is incompatible with an infectious origin. In several vertebrate species, the specific agents responsible for leukaemia belong to a class that is notoriously difficult to isolate. Also, many infectious illnesses do not cluster because they are uncommon responses to the relevant infection. Thus, the agent responsible for infectious mononucleosis is mainly spread not by those with the illness but by that very much larger number of infected individuals who are clinically unaffected (or only trivially so). Such infections can be considered as 'mainly immunising': they can be seen as representing the most probable broad category to which the infection underlying childhood leukaemia belongs.

The concurrent occurrence of Leishmania chagasi infection and childhood acute leukemia in Brazil

Objective

This study investigated the co-existence of Leishmania chagasi infection and childhood leukemia in patients naïve to treatment; this has serious clinical and epidemiological implications.

Methods

The seroprevalence of L. chagasi antibodies prior to any treatment was investigated in children with clinical features of acute leukemia. Serological tests were performed in 470 samples drawn from under 14-year-old children from different regions of Brazil with clinical suspicion of acute leukemia. Acute leukemia subtypes were characterized by immunophenotyping using flow cytometry. Morphological analyses of bone marrow aspirates were systematically performed to visualize blast cells and/or the formation of L. chagasi amastigotes. Data analysis used a standard univariate procedure and the Pearson's chi-square test.

Results

The plasma of 437 children (93%) displayed antibodies against L. chagasi by indirect immunofluorescence assay and enzyme-linked immunosorbent assay tests. Of the 437 patients diagnosed from 2002 to 2006, 254 had acute lymphoblastic leukemia, 92 had acute myeloid leukemia, and 91 did not have acute leukemia. The seroprevalence of L. chagasi antibodies according to the indirect immunofluorescence assay test (22.5%) was similar in children with or without acute leukemia (p-value = 0.76). The co-existence of visceral leishmanasis and acute leukemia was confirmed in 24 children. The overall survival of these children was poor with a high death rate during the first year of leukemia treatment.

Conclusion

In the differential diagnosis of childhood leukemia, visceral leishmanasis should be considered as a potential concurrent disease in regions where L. chagasi is endemic.

Pattern of Acute Lymphoblastic Leukemia Among Kurdish Children in Duhok City, Northern Iraq

Although it is a common malignancy, there is a lack of information about leukemias in Kurdish people. To evaluate the pattern of acute lymphoblastic leukemia among Kurdish children in Duhok city/ North of Iraq, and to compare it with available data from other countries, 83 cases were studied of acute lymphoblastic leukemia diagnosed by bone marrow aspiration cytology, cytochemistry and immune-phenotyping between July 2006 and August 2010.

Data recorded included age, sex, area of residence whether rural or urban, socio-economic status, the presenting features and the initial peripheral blood and bone marrow findings. Ages ranged from 7 months to 14.5 years, the peak occurrence was between one and five years and the male to female ratio was 1.7:1. Most patients were low socio-economic class (86.7%), and 68% were living in rural areas.

The most frequent presenting features were pallor (88%) and bleeding tendency (65%), and 25.2% of patients had a leukocyte count above 50,000 per cubic millimetre. L1 and L2 morphology was approximately equal (51.6% and 46.9%, respectively). The percentage of T-cell ALL was higher than the range reported in other countries. Conclusion: Acute lymphoblastic leukemia is an important health problem in Kurdistan region and its pattern differs in certain respects from that reported from different regions of the world though comparable in other aspects. The study recommends implementation of preventive, diagnostic and therapeutic strategies for leukemias in the Kurdistan region.

Childhood leukemia incidence in Brazil according to different geographical regions

BACKGROUND

Resource-rich countries tend to have a higher incidence of childhood acute lymphoblastic leukemia (ALL), whereas lower rates are seen in more deprived countries. This study describes the incidence of childhood acute leukemia in Brazil, an upper middle-income country, based on data from 16 population-based cancer registries (PBCRs).

PROCEDURE

Data were examined from 16 PBCRs in Brazilian cities located in five geographical regions during the period from 1997 to 2004. Incidence rates were analyzed according to gender, age, and type of leukemia. The Wilcoxon test was performed to evaluate for gender-age based difference between by leukemia type.

RESULTS

The median age-adjusted incidence rate (AAIR) of leukemia in children aged 0-14 years old was 53.3 per million. A different AAIR was found regarding ALL and myeloproliferative disorders (MPD) that ranged from 24.8 to 76.84 per 1,000,000 children. Manaus, although located in a poor area of Brazil, exhibited the highest AAIR (56.6 per million) of ALL. Goiania had the highest AAIR (24.5 per million) of MPD. The median age-specific incidence rate (ASIR) for the 16 Brazilian PBCRs demonstrated a marked peak in incidence of ALL at age 3 years old, in both genders.

CONCLUSIONS

This population-based study of childhood leukemia demonstrates that substantial regional differences exist regarding the incidence of acute leukemia in Brazil, which warrants further ecological study.

Childhood leukaemia, nuclear sites, and population mixing

The excess of childhood leukaemia (CL) in Seascale, near the Sellafield nuclear reprocessing site in rural NW England, suggested that an epidemic of an underlying infection, to which CL is a rare response, is promoted by marked population mixing (PM) in rural areas, in which the prevalence of susceptibles is higher than average. This hypothesis has been confirmed by 12 studies in non-radiation situations. Of the five established CL excesses near nuclear sites, four are associated with significant PM; in the fifth, the Krummel power station in Germany, the subject has not been thoroughly investigated.

Population mixing, socioeconomic status and incidence of childhood acute lymphoblastic leukaemia in England and Wales: analysis by census ward

In this population-based study of acute lymphoblastic leukaemia (ALL) diagnosed among children aged under 15 years in England and Wales during 1986-1995, we analysed incidence at census ward level in relation to a range of variables from the 1991 census, which could be relevant to theories of infectious aetiology. 'Population-mixing' measures, used as surrogates for quantity and diversity of infections entering the community, were calculated from census data on the origins and destinations of migrants in the year before the census. Incidence at ages 1-4 years tended independently to be higher in rural wards, to increase with the diversity of origin wards from which in-migrants had moved during the year before the census, and to be lower in the most deprived areas as categorised by the Carstairs index. This last association was much weaker when urban/rural status and in-migrants' diversity were allowed for. There was no evidence of association with population mixing or deprivation for ALL diagnosed at ages 0 or 5-14 years. The apparent specificity to the young childhood age group suggests that these associations are particularly marked for precursor B-cell ALL, with the disease more likely to occur when delayed exposure to infection leads to increased immunological stress, as predicted by Greaves. The association with diversity of incomers, especially in rural areas, is also consistent with the higher incidence of leukaemia predicted by Kinlen, where population mixing results in below average herd immunity to an infectious agent.

Residential mobility and risk of childhood acute lymphoblastic leukaemia: an ecological study

We conducted an ecological analysis of childhood acute lymphoblastic leukaemia-incidence data from children ⩽5 years old during 1992–1998 from the Surveillance, Epidemiology, and End Results Program in 200 counties and Hawaii. The response variable was the count of cases in each county race–sex stratum, examined in relation to data from the United States Census and the United States Department of Agriculture. The final models for both sexes included race, proportion moved during 1985–1990, and proportion of households with income ⩾$5000 as potential predictors. Incidence was lower among black boys (rate ratio (RR)=0.5) and black girls (RR=0.4) than among other children of the same sex; no other significant racial differences were detected. Incidence was elevated among males (but not females) residing in counties where ⩾50% of the population relocated (RR=1.5) and among females (but not males) residing in counties where <6% of the households had incomes <$5000 (RR=1.5). These sex differences in risk factors were unexpected.

Childhood leukaemia and socioeconomic status: fact or artefact? A report from the United Kingdom childhood cancer study (UKCCS)

BACKGROUND

It is widely believed that children of high socioeconomic status (SES) are more likely than those of low SES to develop acute lymphoblastic leukaemia (ALL). Such observations have led to wide-ranging speculations about the potential aetiological role of factors associated with affluence and modernization.

METHODS

Children (0-14 years) newly diagnosed with cancer in the UK between 1991 and 1996 were ascertained via a rapid hospital-based case finding system (n = 4430, of which 1578 were ALL). Children without cancer (controls) were randomly selected from primary care population registries for comparative purposes (n = 7763). Area-based deprivation scores were assigned as markers of SES at two time points - birth and diagnosis. An individual-based marker of SES - social class - was assigned using father's occupation as recorded on the child's birth certificate.

RESULTS

No differences in area-based measures of deprivation were observed between cases and controls at time of diagnosis, either for all cancers combined [n = 4430, odds ratio (OR) = 1.00 (95% confidence intervals (CI) 0.98-1.01)] or for ALL alone (n = 1578 OR = 0.99, 95%CI 0.96-1.01). Findings were similar at time of birth (all cancers, OR = 0.99 95%CI 0.98-1.01, ALL OR = 0.98, 95%CI 0.96-1.00). In addition, no case-control differences were observed when an individual-based measure of SES - social class - based on father's occupation at time of birth was used.

CONCLUSIONS

The comprehensive nature of the data, coupled with complete case-ascertainment and representative population-based controls suggests that SES in the UK is not a determinant of ALL in children. We believe the small effects reported for SES in some past studies may be artefactual.

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.

Urbanisation and incidence of acute lymphocytic leukaemia among United States children aged 0-4

Acute lymphocytic leukaemia (ALL) incidence among children under 5 years of age was examined, utilising data from 24 United States cancer registries. County-based incidence rates among white children were compared across four levels of urbanisation: large and small metropolitan counties, and adjacent and nonadjacent rural counties. In metropolitan areas, the incidence of ALL was lower among blacks (rate ratio (RR)=0.38, confidence interval (CI)=0.33–0.44) and among Asians/Pacific Islanders (RR=0.78, CI=0.63–0.97) than among whites. Among white children, the incidence of ALL decreased across the four strata of urbanisation, from 67 to 62 to 65 to 54 cases per million person-years at-risk (two-sided trend P=0.009), such that rates were significantly lower in the most remote rural counties than in the most populous metropolitan counties (RR=0.80, 95% CI=0.70–0.91).

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.

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.

Childhood leukaemia incidence and the population mixing hypothesis in US SEER data

We evaluated the infectious aetiology hypothesis of childhood leukaemia that rapid population influx into rural areas is associated with increased risk. Using data from the US SEER program, we found that in changes in rural county population sizes from 1980 to 1989 were associated with incidence rates for childhood acute lymphocytic leukaemia (ALL). The observed associations were strongest among children 0-4 years of age, born in the same state as diagnosis, in extremely rural counties, and when counties adjacent to nonrural counties were excluded. Similar analyses for brain and central nervous system (CNS) cancer in children, a disease less linked to this infectious hypothesis, provide evidence against methodologic bias. Similar evaluations for other decades were not meaningful due to limited sample sizes and, perhaps, increased population mobility.

Geographical and ecological analyses of childhood acute leukaemias and lymphomas in north-west England

Childhood leukaemias and lymphomas have been associated with exposure to environmental factors, including infections, which show geographical variation. This study examined the geographical distribution of the incidence of acute leukaemia and lymphoma using Manchester Children's Tumour Registry (MCTR) data 1976-2000. A total of 910 children were included, all of whom had histologically and/or cytologically verified leukaemia or lymphoma. At the time of their diagnoses, all the children were aged 0-14 years and were resident in the counties of Greater Manchester or Lancashire. Standardized morbidity ratios were calculated. Poisson regression was used to examine the relationship between incidence rates and small-area (census ward) population density, ethnic composition and deprivation index. There was a monotonic relationship between acute lymphoblastic leukaemia (ALL) incidence and population density (P = 0.05). Higher rates were seen in more densely populated areas. There was evidence for a monotonic relationship between the incidence of the mixed cellularity subtype of Hodgkin's disease (HD) and the Townsend deprivation score (P = 0.001). Markedly higher incidence was associated with greater levels of unemployment and household overcrowding. The results for ALL and mixed cellularity HD support the involvement of environmental factors, such as infections, in disease aetiology.

Perinatal exposure to infection and risk of childhood leukemia

BACKGROUND

A population-based case-control study was conducted to investigate the association between childhood leukemia and infectious exposures during pregnancy and early neonatal period.

PROCEDURE

Children born and diagnosed with leukemia between 1973 and 1989 in Sweden (578 lymphatic, 74 myeloid) were selected as cases. One control was randomly selected for each case and individually matched by sex, month, and year of birth. Children with Down's syndrome were excluded. Exposure data were blindly abstracted from antenatal, obstetric, and other standardized medical records. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by conditional logistic regression.

RESULTS

A history of maternal infection was not significantly associated with childhood leukemia, OR = 1.25 (95% CI 0.95-1.65). Maternal lower genital tract infection significantly increased the risk of childhood leukemia, OR = 1.78 (95% CI 1.17-2.72), and especially for children over 4 years of age at diagnosis, OR = 2.01 (95% CI 1.12-3.80). Neonatal infection was not associated with the risk of leukemia. The results remained unaltered after adjustment for potential confounders, and separate analyses for myeloid and lymphoid leukemia.

CONCLUSIONS

We could document an association between exposure to maternal lower genital tract infection in utero, and a subsequent risk for childhood leukemia, which indicate the importance of an early exposure.

Acute lymphoblastic leukemia incidence during socioeconomic transition: selective increase in children from 1 to 4 years

Pre-school acute lymphoblastic leukemia (ALL) peak is consistent in developed but not in developing countries and its magnitude apparently correlates with the socioeconomic status. A population-based study describing ALL incidence during socioeconomic transition has been lacking. Central European post-communist countries (with very low foreign migration and centralized statistics) offer reliable data for the period before and during major socioeconomic changes. Population-based data on Czech ALL patients younger than 18 years were taken from two independent Czech national registries partially overlapping in time (1980-1998, n = 1236 and 1991-1999, n = 570). During the 1980s and 1990s, ALL incidence among children 1-4 years increased 1.5 times (P = 0.01). This increase was more prominent in females than in males (slopes 0.13 and 0.09, P values 0.03 and >0.05, respectively). No significant change was observed in other age groups (0, 5-9, 10-14, 15-17 years or all others combined). We discuss possible underlying socioeconomic factors including infant care and breast-feeding, hygiene, birth order, industry and pollution. Moreover, we try to pinpoint the immunophenotypic/molecular-genetic subsets of ALL that might be socioeconomically affected. Selective increase of ALL in children 1-4 years old provides epidemiological evidence that etiology and/or trigger mechanisms are different for a considerable proportion of these children and that these mechanisms are exogenous.

Markers of infection, breast-feeding and childhood acute lymphoblastic leukaemia

Infections are suspected to play a role in the aetiology of childhood leukaemia. In 1989-95, we evaluated the relation between childhood acute lymphoblastic leukaemia and pre- and postnatal markers of exposure to infection, as well as breast-feeding. A population-based case-control study was carried out in certain regions of Québec, Canada, in 1989-95 including 491 incident cases diagnosed between 1980 and 1993 and aged between 0 and 9 years. An identical number of healthy controls matched for age, sex and region of residence at the date of diagnosis was included. Having older siblings, mother's use of antibiotics during pregnancy, and being born second or later were all associated with increased risk of leukaemia while early day-care attendance (odds ratio (OR) = 0.49; 95% CI 0.31-0.77), and breast-feeding (OR = 0.68; 95% CI 0.49-0.95) were significantly protective. A marker of population mixing was not a risk factor. When including all variables defining family structure in a model, having older siblings at time of diagnosis was a risk factor among children diagnosed before 4 years of age (OR = 4.54; 95% CI 2.27-9.07) whereas having older siblings in the first year of life was protective among children diagnosed at 4 years of age or later (OR = 0.46; 95% CI 0.22-0.97).

Quantifying the effect of population mixing on childhood leukaemia risk: the Seascale cluster

A statistical model was developed based on Poisson regression of incidence of childhood leukaemia and non-Hodgkin's lymphoma (NHL) in relation to population mixing among all 119 539 children born 1969-1989 to mothers living in Cumbria, north-west England, (excluding Seascale). This model was used to predict the number of cases in Seascale (the village adjacent to the Sellafield nuclear installation) children, born 1950-1989 and diagnosed before 1993. After allowing for age, the incidence of acute lymphoblastic leukaemia (ALL) and NHL was significantly higher among children born in areas with the highest levels of population mixing, relative risk (RR) = 11.7 (95% confidence interval (CI) 3.2-43) and was highest among children of incomers. The model predicted up to 3.0 (95% CI 1.3-6.0) cases of ALL/NHL in children born in Seascale compared to six observed and 2.0 (95% CI 1.0-3.4) cases in children resident, but not born, in Seascale compared to two observed. Population mixing is a significant risk factor for ALL/NHL, especially in young children, accounting for over 50% of cases in Cumbria and most cases in Seascale.

Population density and childhood leukaemia: results of the EUROCLUS Study

The EUROCLUS study assembled incidence data for 13,551 cases of childhood leukaemia (CL) diagnosed between 1980 and 1989 in 17 countries (or regions of countries). These were referenced by location at diagnosis to small census areas of which there were 25,723 in the study area. Population counts, surface area and, hence, population density were available for all these small areas. Previous analyses have shown limited extra-Poisson variation (EPV) of case counts within small areas; this is most pronounced in areas of intermediate population density (150-499 persons/km2). In this study, the data set was examined in more detail for evidence that variations in incidence and EPV of CL are associated with population density. Incidence showed a curvilinear association with population density and was highest in areas which were somewhat more densely populated (500-750 persons/km2), where the incidence rate ratio relative to areas having > or = 1000 persons/km2 was 1.16 (95% confidence interval 1.07-1.26) and the P value for quadratic trend across eight strata of population density was 0.02. Incidence in these areas is uniformly elevated and showed no evidence of heterogeneity (i.e. EPV). Statistically significant evidence of EPV was evident amongst some of the areas previously classified as intermediate density areas (specifically, those with a density of 250-499 persons/km2, P < 0.001 for CL). These results were interpreted in terms of the current aetiological hypotheses for CL which propose that exposure to localised epidemics of one or more common infectious agent may contribute to the development of leukaemia. They suggest that such epidemics arise regularly in moderately densely populated areas and also sporadically in areas which are somewhat less densely populated. Although other interpretations are possible, these results may assist in the identification of characteristics which infectious agents must possess if direct or indirect causes of CL.

Evidence that an HLA-DQA1-DQB1 haplotype influences susceptibility to childhood common acute lymphoblastic leukaemia in boys provides further support for an infection-related aetiology

Comparison of DQA1 and DQB1 alleles in 60 children with common acute lymphoblastic leukaemia (c-ALL) and 78 newborn infant control subjects revealed that male but not female patients had a higher frequency of DQA1*0101/*0104 and DQB1*0501 than appropriate control subjects. The results suggest a male-associated susceptibility haplotype in c-ALL and supports an infectious aetiology.

Lack of association between childhood common acute lymphoblastic leukaemia and an HLA-C locus dimorphism influencing the specificity of natural killer cells

Previous serological studies documenting an association between acute lymphoblastic leukaemia (ALL) and HLA-Cw antigens suggested that the HLA-C locus might influence susceptibility to ALL. However, associations with more than one Cw antigen suggest that polymorphic variants shared by more than Cw allele could be involved. Recent studies have shown that the HLA-C locus encodes two ligands (NK1 and NK2) recognized by receptors on natural killer (NK) cells. HLA-Cw alleles encoding these ligands are dimorphic, dependent on whether they encode one or other NK ligand. To determine whether susceptibility to the common (CD10+) form of childhood ALL (c-ALL) is associated with NK1 or NK2, we carried out a molecular analysis of 94 childhood c-ALL patients and 136 infant controls. We found no difference in the frequency of NK1 and NK2 alleles, phenotypes or genotypes between the patients and controls, suggesting that this does not explain the role of the HLA-C locus in susceptibility to childhood c-ALL.

Childhood incidence of acute lymphoblastic leukaemia and exposure to broadcast radiation in Sydney--a second look

INTRODUCTION

Recent findings of an apparent association between incidence of childhood leukaemia and radio frequency radiation (RFR) from television transmission antennas in Sydney, NSW, are examined.

METHODS

Incidence of childhood (0-14 years) acute lymphoblastic leukaemia (ALL) at the local government area (LGA) level is related to estimated exposure levels of RFR from television transmission antennas, using Poisson regression techniques.

RESULTS

Most of the association between ALL incidence and television transmission RFR is shown to be the result of an influential observation: one of the highly exposed LGAs contributes all the excess, while in a similarly exposed LGA childhood ALL incidence was found to be no higher than the rate expected for NSW. With the influential observation excluded from the analysis, no positive correlation between exposure to RFR and leukaemia is evident. Conversely, under the assumption of an association with RFR, the low probability of the observed incident cases in LGAs under conditions of relatively high exposure to RFR conflicts with the assumption of an effect.

CONCLUSION

The apparent association between childhood ALL incidence and RFR radiation from television towers is weaker when an LGA-level analysis is conducted.

Spatial temporal patterns in childhood leukaemia: further evidence for an infectious origin. EUROCLUS project

The EUROCLUS project included information on residence at diagnosis for 13351 cases of childhood leukaemia diagnosed in the period 1980-89 in defined geographical regions in 17 countries. A formal algorithm permits identification of small census areas as containing case excesses. The present analysis examines spatial-temporal patterns of the cases (n = 970) within these clustered areas. The objectives were, first, to compare these results with those from an analysis conducted for UK data for the period 1966-83, and, second, to extend them to consider infant leukaemias. A modification of the Knox test investigates, within the small areas, temporal overlap between cases in a subgroup of interest at a putative critical time and all other cases at any time between birth and diagnosis. Critical times were specified in advance as follows: for cases of acute lymphoblastic leukaemia aged 2-4 years, the 18-month period preceding diagnosis; for cases of total leukaemia aged 5-14 years, 1 year before to 1 year after birth; and for infant cases (diagnosed < 1 year), 1 year before to 6 months after birth. Each of the analyses found evidence of excess space-time overlap compared with that expected; these were 10% (P = 0.005), 15% (P= 0.0002) and 26% (P= 0.03) respectively. The results are interpreted in terms of an infectious origin of childhood leukaemia.

Skin changes in "screen dermatitis" versus classical UV- and ionizing irradiation-related damage--similarities and differences

An increasing number of persons say that they get cutaneous problems as well as symptoms from certain internal organs, such as the central nervous system (CNS) and the heart, when being close to electric equipment. A major group of these patients are the users of video display terminals (VDTs), who claim to have subjective and objective skin- and mucosa-related symptoms, such as pain, itch, heat sensation, erythema, papules, and pustules. The CNS symptoms are, e.g. dizziness, tiredness, and headache. Erythema, itch, heat sensation, edema and pain are also common symptoms of sunburn (UV dermatitis). Alterations have been observed in cell populations of the skin of patients suffering from so-called "screen dermatitis" similar to those observed in the skin damaged due to ultraviolet (UV) light or ionizing radiation. In "screen dermatitis" patients a much higher number of mast cells have been observed. It is known that UVB irradiation induces mast cell degranulation and release of TNF-alpha. The high number of mast cells present in the "screen dermatitis" patients and the possible release of specific substances, such as histamine, may explain their clinical symptoms of itch, pain, edema and erythema. The most remarkable change among cutaneous cells, after exposure with the above-mentioned irradiation sources, is the disappearance of the Langerhans' cells. This change has also been observed in "screen dermatitis" patients, again pointing to a common cellular and molecular basis. The results of this literature study demonstrate that highly similar changes exist in the skin of "screen dermatitis" patients, as regards the clinical manifestations as well as alterations in the cell populations, and in skin damaged by UV light or ionizing radiation.

Higher Frequency of Glutathione S-Transferase Deletions in Black Children With Acute Lymphoblastic Leukemia

The genetic polymorphisms in human glutathione S-transferases (GST) M1 and T1 have been associated with race, disease risk, and outcome of some adult cancers. Also, there are racial differences in the incidence and characteristics of childhood acute lymphoblastic leukemia (ALL). Our objectives were to compare the frequency of the null genotype for GSTM1, GSTT1, or both in children with ALL to that in healthy controls, and to determine whether GST genotype was associated with treatment outcome and prognostic factors. We studied GSTM1 and GSTT1 genotypes in somatic cell DNA from black children and white children with ALL and in 416 healthy controls, using a polymerase chain reaction technique. Ninety of 163 (55.2%) white ALL patients and 14 of 34 (41.2%) black patients were GSTM1 null, frequencies not significantly different (P = .19) than healthy controls (53.5% in whites and 27.6% in blacks), although there was a trend toward more null genotypes in black ALL patients. Twenty-three of 163 (14.1%) white ALL patients and 12 of 34 (35.3%) black ALL patients were GSTT1 null, not different (P = .34) than the frequencies in healthy controls (15.0% in whites and 24.1% in blacks). However, the frequency of the “double-null” genotype, lacking both GSTM1 and GSTT1, was higher in black patients with ALL (8 of 34 or 23.5%) than in black controls (3.9%) (P = .0005), but this was not the case in white patients with ALL (10 of 163 or 6.1%) compared to white controls (8.0%) (P = .68). In stratified analyses, the GST double-null genotype was not associated with other characteristics that might differ between whites and blacks with ALL, such as age, T-lineage immunophenotype, presenting white blood cell count, DNA index, or insurance status. The null genotype for GSTM1, GSTT1, or both was not found to be a prognostic factor for disease-free survival or probability of hematologic remission; central nervous system relapse tended to be less common in those with the GSTM1 null genotype (P = .054) . The double-null genotype for GSTM1 and GSTT1 is more common among blacks but not whites with childhood ALL. These data suggest that GST genotype, coupled with unidentified additional risk factors, may play a role in risk of childhood ALL in American blacks.

Higher Frequency of Glutathione S-Transferase Deletions in Black Children With Acute Lymphoblastic Leukemia

The genetic polymorphisms in human glutathione S-transferases (GST) M1 and T1 have been associated with race, disease risk, and outcome of some adult cancers. Also, there are racial differences in the incidence and characteristics of childhood acute lymphoblastic leukemia (ALL). Our objectives were to compare the frequency of the null genotype for GSTM1, GSTT1, or both in children with ALL to that in healthy controls, and to determine whether GST genotype was associated with treatment outcome and prognostic factors. We studied GSTM1 and GSTT1 genotypes in somatic cell DNA from black children and white children with ALL and in 416 healthy controls, using a polymerase chain reaction technique. Ninety of 163 (55.2%) white ALL patients and 14 of 34 (41.2%) black patients were GSTM1 null, frequencies not significantly different (P = .19) than healthy controls (53.5% in whites and 27.6% in blacks), although there was a trend toward more null genotypes in black ALL patients. Twenty-three of 163 (14.1%) white ALL patients and 12 of 34 (35.3%) black ALL patients were GSTT1 null, not different (P = .34) than the frequencies in healthy controls (15.0% in whites and 24.1% in blacks). However, the frequency of the “double-null” genotype, lacking both GSTM1 and GSTT1, was higher in black patients with ALL (8 of 34 or 23.5%) than in black controls (3.9%) (P = .0005), but this was not the case in white patients with ALL (10 of 163 or 6.1%) compared to white controls (8.0%) (P = .68). In stratified analyses, the GST double-null genotype was not associated with other characteristics that might differ between whites and blacks with ALL, such as age, T-lineage immunophenotype, presenting white blood cell count, DNA index, or insurance status. The null genotype for GSTM1, GSTT1, or both was not found to be a prognostic factor for disease-free survival or probability of hematologic remission; central nervous system relapse tended to be less common in those with the GSTM1 null genotype (P = .054) . The double-null genotype for GSTM1 and GSTT1 is more common among blacks but not whites with childhood ALL. These data suggest that GST genotype, coupled with unidentified additional risk factors, may play a role in risk of childhood ALL in American blacks.

Incidence of childhood leukaemia and non-Hodgkin's lymphoma in the vicinity of nuclear sites in Scotland, 1968-93

OBJECTIVES

The primary aims were to investigate the incidence of leukaemia and non-Hodgkin's lymphoma in children resident near seven nuclear sites in Scotland and to determine whether there was any evidence of a gradient in risk with distance of residence from a nuclear site. A secondary aim was to assess the power of statistical tests for increased risk of disease near a point source when applied in the context of census data for Scotland.

METHODS

The study data set comprised 1287 cases of leukaemia and non-Hodgkin's lymphoma diagnosed in children aged under 15 years in the period 1968-93, validated for accuracy and completeness. A study zone around each nuclear site was constructed from enumeration districts within 25 km. Expected numbers were calculated, adjusting for sex, age, and indices of deprivation and urban-rural residence. Six statistical tests were evaluated. Stone's maximum likelihood ratio (unconditional application) was applied as the main test for general increased incidence across a study zone. The linear risk score based on enumeration districts (conditional application) was used as a secondary test for declining risk with distance from each site.

RESULTS

More cases were observed (O) than expected (E) in the study zones around Rosyth naval base (O/E 1.02), Chapelcross electricity generating station (O/E 1.08), and Dounreay reprocessing plant (O/E 1.99). The maximum likelihood ratio test reached significance only for Dounreay (P = 0.030). The linear risk score test did not indicate a trend in risk with distance from any of the seven sites, including Dounreay.

CONCLUSIONS

There was no evidence of a generally increased risk of childhood leukaemia and non-Hodgkin's lymphoma around nuclear sites in Scotland, nor any evidence of a trend of decreasing risk with distance from any of the sites. There was a significant excess risk in the zone around Dounreay, which was only partially accounted for by the sociodemographic characteristics of the area. The statistical power of tests for localised increased risk of disease around a point source should be assessed in each new setting in which they are applied.

Effect of population mixing and socioeconomic status in England and Wales, 1979-85, on lymphoblastic leukaemia in children

OBJECTIVE

To examine the effects of migration, diversity of migrant origins, commuting, and socioeconomic status on the incidence of acute lymphoblastic leukaemia in childhood.

DESIGN

Poisson regression analysis of incidence rates in relation to the variables of interest.

SETTING

The 403 county districts of England and Wales during 1979-85.

SUBJECTS

Children aged under 15 years.

RESULTS

There were significant trends in the incidence of lymphoblastic leukaemia at ages 0-4 and 5-9 years with the proportion of children in a district who had recently entered the district. While there was no consistent relation between the proportion of recent incomers in the total population of a district and its incidence rate, the combination of higher migration with greater diversity of origins or distance moved was associated with higher incidence in both age groups. Incidence increased significantly at age 0-4 with the level of employment in a district and at age 5-9 with the proportion of households with access to a car. No significant trends were found with commuting.

CONCLUSIONS

The results for level of child migration and diversity of total migration provide evidence of an effect of population mixing on the incidence of childhood leukaemia which is not restricted to areas experiencing the most extreme levels of mixing.

Isolation, car ownership, and small area variation in incidence of acute lymphoblastic leukaemia in children

To determine whether increased rates of childhood acute lymphoblastic leukaemia (ALL) which had been reported in isolated areas could be attributed to higher proportions of households owning cars, ecological analysis was performed with electoral wards as area units. Previous data were re-analysed using the proportion of households having no car, taken from the 1981 census of England and Wales, as an additional explanatory factor. A specialist registry of haematopoietic malignancies covering one-third of England and Wales (3270 electoral wards) recorded 438 cases of ALL in children diagnosed 1984-89, including 304 in the childhood peak (at ages 1-7 years). Relative risks were derived by Poisson regression of total childhood ALL and at ages 1-7 years for groups of electoral wards classified by isolation and car ownership. Multivariable analyses included adjustment for socio-economic status. No evidence of increased risk of childhood ALL in areas where more households own cars was found. ALL at ages 1-7 years was inversely associated with car ownership (risk in wards with least cars relative to those with most cars = 2.28, 95% CI: 1.12-4.64). The associations with geographic isolation persisted after allowing for car ownership (risks for ALL in young children in isolated relative to built-up areas = 2.19, 95% CI: 1.44-3.33). Levels of car ownership cannot explain the increased rates of childhood ALL which have been observed in isolated areas. No support has been found for a hypothesis relating these excesses to benzene exposure of children transported in cars. The previous explanation for the small area variation of childhood ALL in terms of geographical isolation and interpretation in terms of exposure to common infections continues to be justified.

Space-time clustering of childhood leukaemia in Greece: evidence supporting a viral aetiology

The method introduced by Knox for evaluation of space-time clustering has been applied to 872 cases of childhood (0-14 year old) leukaemia diagnosed in Greece over the 10 year period 1980-89. Greek towns are characterised by substantial population mixing due to internal migration, whereas there is relative isolation in mountainous rural areas. Predetermined space (5 km) and time (1 year) limits were used on the basis of previous reports in order to define the clustering cell. There is highly significant evidence for clustering of childhood leukaemia in Greece as a whole, the observed number of pairs that are close in both spaces and time exceeding the expected number by 5.2% (P = 0.004). The excess is particularly evident for leukaemia cases in 0 to 4-year-old children, among whom the observed number of pairs that are close in both space and time exceeded the expected number by 9.4% (P = 0.004). There is no evidence of space-time clustering for leukaemia cases older than 5 years. The overall pattern is descriptively similar in urban and semiurban areas and is especially marked for acute lymphoblastic leukaemia at the childhood peak ages (2-4 years) with an excess of 19% (P = 0.0006). In the rural population there is evidence for clustering of cases belonging to older and broader age groups, a phenomenon compatible with a delay in the development of herd immunity against putative infectious aetiological agents. The findings of the present study provide support for the hypothesis that a substantial proportion of cases of childhood leukaemia may arise as a rare sequel to exposure to an agent or agents, most probably viral in nature.

Explaining urban-rural variations in health: a review of interactions between individual and environment

In order to gain insight into the relation between health and people's environment, literature published between 1985 and 1994 was gathered from several international databases. An introduction into existing theory regarding geographic disparities is presented: geographical drift and breeder hypotheses are discussed. This is followed by a critical review focusing on interaction effects of urbanicity and individual characteristics on health. This leads to two major conclusions. First, emphasis in past research has been primarily on urban constraints rather than opportunities. Positive aspects of urban living are often insufficiently appreciated. Second, positive and negative environmental aspects have an effect on health that is often dependent on individual characteristics. The extent to which the environment exerts influence on a person's health is dependent on that person's individual characteristics. These conclusions are relevant only for further developing the breeder hypothesis, however. Large scale individual based longitudinal data should be studied in order to gain more insight into the relative importance of the geographical drift hypothesis.

Spatial variation of natural radiation and childhood leukaemia incidence in Great Britain

This paper describes an analysis of the geographical variation of childhood leukaemia incidence in Great Britain over a 15 year period in relation to natural radiation (gamma and radon). Data at the level of the 459 district level local authorities in England, Wales and regional districts in Scotland are analysed in two complementary ways: first, by Poisson regressions with the inclusion of environmental covariates and a smooth spatial structure; secondly, by a hierarchical Bayesian model in which extra-Poisson variability is modelled explicitly in terms of spatial and non-spatial components. From this analysis, we deduce a strong indication that a main part of the variability is accounted for by a local neighbourhood 'clustering' structure. This structure is furthermore relatively stable over the 15 year period for the lymphocytic leukaemias which make up the majority of observed cases. We found no evidence of a positive association of childhood leukaemia incidence with outdoor or indoor gamma radiation levels. There is no consistent evidence of any association with radon levels. Indeed, in the Poisson regressions, a significant positive association was only observed for one 5-year period, a result which is not compatible with a stable environmental effect. Moreover, this positive association became clearly non-significant when over-dispersion relative to the Poisson distribution was taken into account.

Childhood cancer in Britain: the National Registry of Childhood Tumours and incidence rates 1978-1987

The National Registry of Childhood Tumours contains population-based data on childhood cancers diagnosed throughout Great Britain from 1962 onwards. This paper describes the methodology of the Registry, presents incidence rates for 1978-1987 and describes other uses of the data. Total age-standardised annual incidence was 118.3 per million. The most frequent diagnostic groups were leukaemias (age-standardised rate 39.8), brain and spinal tumours (27.0), lymphomas (11.1), sympathetic nervous system tumours (8.3), kidney tumours (7.7) and soft-tissue sarcomas (7.5). Incidence rates were similar to those reported from other Western industrialised countries. The data are also used for a wide range of epidemiological and other studies. These include analyses of geographical variations in incidence, trends in survival, health of long-term survivors and their offspring and the genetics of childhood cancer. Information is frequently provided for clinicians and research workers, and series of specific types of cancer are compiled for further study. The Registry depends for the completeness and accuracy of its data on a wide range of organisations and individuals, and it is essential that this cooperation continues if the Registry is to be maintained.

Immunological subtypes of childhood acute lymphoblastic leukemia in Bulgaria

With regards to the geographical variation in acute lymphoblastic leukemia (ALL) distribution, we present data from the immunophenotyping of 171 newly diagnosed cases of childhood ALL in Bulgaria during a 4 year period (1990-1994). On the basis of 17 phenotypic markers the distribution of immunological subtypes was as follows: AUL 4%; Pro-B ALL 13%; common ALL 42%; Pre-B ALL 11%; B-ALL 1%; T-ALL 28% and unclassified 2%. Most of the cases were between 2 and 5 years of age. Common ALL was predominant (53%) in this age group. The male:female ratio was 1.7:1. The frequency of T-ALL (28%) was significantly higher (P < 0.01; t = 3.49) in comparison to that reported for the U.S.A. and West European countries (mean 13%). It was close to the frequency reported by some authors for France (20%), Greece (26%) and south Italy (28.1%). These countries and Bulgaria might form an environmental area with a moderate frequency of T-ALL.

Childhood leukemia in metropolitan regions in the United States: a possible relation to population density?

Following recent research in Great Britain, the geographic incidence of leukemia and non-Hodgkin's lymphoma among White children in three metropolitan regions of the United States (San Francisco-Oakland, CA; Detroit, MI; and Atlanta, GA) during 1978-82 has been analyzed using census tract-specific data. There was no evidence of a general tendency for cases to cluster geographically, in contrast to results from Britain. Further, rates did not vary with median income or education levels for census tracts. However, there was a statistically significant increasing trend in incidence rates with increasing population density: relative risk for highest relative to lowest category = 1.4 (95% percent confidence interval [CI] = 1.1-2.0) for White population density, and 1.4 (CI = 1.0-2.0) for total population density. The interpretation of these findings is unclear and further investigation is required. It is possible that population density is acting as a surrogate for some virus-related factor.

Childhood Acute Lymphoblastic Leukemia: A Cluster in Southwestern Sardinia (Italy)

In response to public concern about an increase in the incidence of leukemia among children in southwestern Sardinia (Italy), incident cases of childhood cancer (ages 0-14) were ascertained among residents in the province of Cagliari, which comprises all of southern Sardinia, in 1974-89. Completeness of the ascertainment of leukemia cases was validated by comparison with estimates derived from official statistics of mortality and survival curves. A significant excess risk of childhood acute lymphoblastic leukemia (cALL) was found for children residing in the town of Carbonia. The risk was highest in 1983-85, when seven cases occurred versus 0.8 expected. No birth-cohort effect was observed. The cALL incidence rate was significantly higher among children born and residing in Carbonia than among children born in Carbonia but residing elsewhere. However, the cALL cases did not cluster within the town of Carbonia. The proximity of the largest industrial settlement in the region of Sardinia raised the suspicion that environmental pollution was responsible for the observed excess. Information about industrial emissions from this settlement prior to the appearance of the cALL cluster was not sufficient to reject or confirm the hypothesis.

Childhood malignancies in Germany--methods and results of a nationwide registry

Since 1980, a nationwide registry of childhood malignancies has been established in the Federal Republic of Germany. The registry combines features of a population-based and a hospital-based registry. Basic registry data are complemented and validated by data from all ongoing clinical trials in paediatric oncology. Descriptive analyses are presented for the first 13 years of operation of the registry. In addition, time trends and regional variations of incidence within the Federal Republic of Germany are shown. A brief description of completed and ongoing registry-based epidemiological studies is given.

Alpha-particle-induced chromosomal instability in human bone marrow cells

alpha-particles, which are ionising radiation of high linear-energy-transfer emitted, for example, from radon or plutonium, pass through tissue as highly structured tracks. Single target cells in the path of the tracks might be damaged by even low-dose alpha-irradiation. We found non-clonal cytogenetic aberrations, characterised by a high frequency of chromatid aberrations with chromosome aberrations, in clonal descendants of haemopoietic stem cells after exposure to alpha-particles of bone marrow cells from two of four haematologically normal individuals (up to 25% abnormal metaphases). The data are consistent with a transmissible genetic instability induced in a stem cell resulting in a diversity of aberrations in its clonal progeny many cell divisions later.

Leukaemia and non-Hodgkin's lymphoma: incidence in children and young adults resident in the Dounreay area of Caithness, Scotland in 1968-91

STUDY OBJECTIVE

To review the incidence of leukaemia and non-Hodgkin's lymphoma in children and young adults in the area less than 25 km from the Dounreay nuclear installation and the remainder of the Kirkwall postcode area in the full time period for which data are now available (1968-91), and to determine whether the excess incidence reported in the period up to 1984 has continued in subsequent years.

DESIGN

Geographical incidence study.

SETTING

The Kirkwall postcode area of Scotland.

SUBJECTS

Children and young adults resident in the area in the period 1968-91.

MAIN RESULTS

Observed numbers of cases of leukaemia and non-Hodgkin's lymphoma and observed to expected ratios with expected numbers based on Scottish national rates were determined. In 1968-91, 12 cases were observed compared with 5.2 expected in the zone < 25 km from the Dounreay plant (p = 0.007). In the latest period, 1985-91, which has not previously been examined, four cases were observed compared with 1.4 expected (p = 0.059).

CONCLUSION

The observation of an excess of borderline statistical significance in 1985-91 following the substantial excess incidence which occurred in the early 1980s suggests that the incidence of leukaemia and non-Hodgkin's lymphoma in this area should continue to be a matter of concern. The phenomenon of high incidences of childhood and young adult leukaemia and lymphoma near some nuclear installations in isolated areas is yet to be explained, but certain aspects of the data examined in the present report are consistent with the hypothesis of an infectious aetiology for leukaemia in very young children.

Leukaemia mortality in French communes (administrative units) with a large and rapid population increase

Higher than expected leukaemia mortality rates have been observed in the persons under 25 years of age living in new towns in Britain. We report the results of a study on persons under 25 residing in all French communes (administrative units) in which a large and rapid population increase occurred between 1968 and 1990. The observed number of leukaemia deaths was 101, slightly less than the 112.0 expected from national mortality statistics. There was no difference in the risk of leukaemia mortality according to sex, age, size of the population increase or region (Ile de France versus others).