Geographical variation in mortality from leukaemia and other cancers in England and Wales in relation to proximity to nuclear installations, 1969-78

A Short Latency between Radiation Exposure from Nuclear Plants and Cancer in Young Children

Previous reports document a short latency of cancer onset in young children exposed to low doses of radioactivity. The standard mortality ratio (SMR) for cancer in children dying before age ten rose in the period 6–10 years after the Three Mile Island and Chernobyl accidents in populations most exposed to fallout. SMRs near most nuclear power plants were elevated 6–10 years after startup, particularly for leukemia. Cancer incidence in children under age ten living near New York and New Jersey nuclear plants increased 4–5 years after increases in average strontium-90 in baby teeth, and declined 4–5 years after Sr-90 averages dropped. The assumption that Sr-90 and childhood cancer are correlated is best supported for a supralinear dose-response, meaning the greatest per-dose risks are at the lowest doses. Findings document that the very young are especially susceptible to adverse effects of radiation exposure, even at relatively low doses.

A three-dimensional point process model for the spatial distribution of disease occurrence in relation to an exposure source

We study methods for how to include the spatial distribution of tumours when investigating the relation between brain tumours and the exposure from radio frequency electromagnetic fields caused by mobile phone use. Our suggested point process model is adapted from studies investigating spatial aggregation of a disease around a source of potential hazard in environmental epidemiology, where now the source is the preferred ear of each phone user. In this context, the spatial distribution is a distribution over a sample of patients rather than over multiple disease cases within one geographical area. We show how the distance relation between tumour and phone can be modelled nonparametrically and, with various parametric functions, how covariates can be included in the model and how to test for the effect of distance. To illustrate the models, we apply them to a subset of the data from the Interphone Study, a large multinational case-control study on the association between brain tumours and mobile phone use.

Epidemiological evidence of childhood leukaemia around nuclear power plants

A few reports of increased numbers of leukaemia cases (clusters) in children living in the vicinity of nuclear power plants (NPP) and other nuclear installations have triggered a heated debate over the possible causes of the disease. In this review the most important cases of childhood leukaemia clusters around NPPs are described and analyzed with special emphasis on the relationship between the environmental exposure to ionizing radiation and the risk of leukaemia. Since, as indicated, a lifetime residency in the proximity of an NPP does not pose any specific health risk to people and the emitted ionizing radiation is too small to cause cancer, a number of hypotheses have been proposed to explain the childhood leukaemia clusters. The most likely explanation for the clusters is 'population mixing', i.e., the influx of outside workers to rural regions where nuclear installations are being set up and where local people are not immune to pathogens brought along with the incomers.

Male-mediated developmental toxicity

Male-mediated developmental toxicity has been of concern for many years. The public became aware of male-mediated developmental toxicity in the early 1990s when it was reported that men working at Sellafield might be causing leukemia in their children. Human and animal studies have contributed to our current understanding of male-mediated effects. Animal studies in the 1980s and 1990s suggested that genetic damage after radiation and chemical exposure might be transmitted to offspring. With the increasing understanding that there is histone retention and modification, protamine incorporation into the chromatin and DNA methylation in mature sperm and that spermatozoal RNA transcripts can play important roles in the epigenetic state of sperm, heritable studies began to be viewed differently. Recent reports using molecular approaches have demonstrated that DNA damage can be transmitted to babies from smoking fathers, and expanded simple tandem repeats minisatellite mutations were found in the germline of fathers who were exposed to radiation from the Chernobyl nuclear power plant disaster. In epidemiological studies, it is possible to clarify whether damage is transmitted to the sons after exposure of the fathers. Paternally transmitted damage to the offspring is now recognized as a complex issue with genetic as well as epigenetic components.

Cancer risk in adult residents near nuclear power plants in Korea - a cohort study of 1992-2010

This study evaluated cancer risk for adult residents near Nuclear Power Plants (NPPs) in Korea through a valid prospective cohort study during 1992-2010. The study cohort was composed of 11,367 adults living within a five km radius from the NPPs for the exposed and 24,809 adults for the non-exposed or reference cohort set at two different levels of proximity; 5-30 km radius and more than 30 km radius away from NPPs. In 303,542.5 person-years of follow-up, a total of 2,298 cancer cases of all sites, or 1,377 radio-inducible cancers diagnosed during 1992-2008 were ascertained. Multiple adjusted hazard ratios and 95% confidence intervals were estimated using multivariate Cox proportional hazard model. There were no epidemiological evidence for increased risk of cancer due to radiation from NPPs. Radiological study results or surveillance data of radiation doses around NPPs could be well documented for risk estimation of radio-inducible cancers, instead of epidemiological study results of the long-time required. Continuous surveillance of quantitative measures of dose levels around NPPs and radiation exposures to the residents is warranted.

Childhood cancers near German nuclear power stations: hypothesis to explain the cancer increases

In early 2008, the very large Kinderkrebs in der Umgebung von Kernkraftwerken [Childhood Cancer near Nuclear Power Plants] (KiKK) study in Germany reported increases in leukaemias and solid cancers among children living near all German nuclear power plants (NPPs). This study, previously described in Medicine, Conflict and Survival, has triggered debates in many countries as to the cause or causes of these increased cancers. An accompanying article reports on the recent developments on the KiKK study including the responses by German radiation agencies, and the results of recent epidemiological studies near United Kingdom and French nuclear installations. This article outlines a possible explanation for the increased cancers. In essence, doses from environmental NPP emissions to embryos/foetuses in pregnant women near NPPs may be larger than suspected, and haematopoietic tissues may be considerably more radiosensitive in embryos/foetuses than in newborn babies. The article concludes with recommendations for further research.

Epidemiological studies of leukaemia in children and young adults around nuclear facilities: a critical review

The existence of an increased risk of childhood leukaemia near nuclear installations is a recurrent issue. A review of the related epidemiological literature is presented here. Results for 198 nuclear sites throughout 10 countries were included in the review. In addition to local studies, 25 multi-site studies have been published for eight countries. A large variability was noticed in the quality of the data as well as in the definition of the study population and in the methods of analysis. Many studies present important limits that make the results difficult to interpret. The review confirms that some clusters of childhood leukaemia cases exist locally. However, results based on multi-site studies around nuclear installations do not indicate an increased risk globally. Many studies were launched to investigate possible origins of the observed clusters around specific sites, but up to now, none of the proposed hypotheses have explained them.

Meta-analysis of standardized incidence and mortality rates of childhood leukaemia in proximity to nuclear facilities

The meta-analysis combined and statistically analysed studies of childhood leukaemia and nuclear facilities. Focus was on studies that calculated standardized rates for individual facilities. Due to variability between study designs, eight separate analyses were performed stratified by age and zone. One hundred and thirty-six sites were used in at least one analysis. Unadjusted, fixed effects and random effects models were used. Meta-rates greater than one were found in all models at all stratification levels often achieving statistical significance. Caution must be used when interpreting these results. The meta-analysis was able to show an increase in childhood leukaemia near nuclear facilities, but does not support a hypothesis to explain the excess. Each type of model utilized has limitations. Fixed effects models give greater weight to larger studies; however, population density may be a risk factor. Random effects models give greater weight to smaller studies that may be more likely to be affected by publication bias. A limitation of the overall study design is that standardized rates must be available for individual sites which led to exclusion of studies that only calculated rates for multiple sites and those that presented other statistical methods. Further, dose-response studies do not support excess rates found near nuclear facilities. However, it cannot be ignored that the majority of studies have found elevated rates, although not usually statistically significant.

Iowa radon leukaemia study: a hierarchical population risk model for spatially correlated exposure measured with error

This paper presents a Bayesian model that allows for the joint prediction of county-average radon levels and estimation of the associated leukaemia risk. The methods are motivated by radon data from an epidemiologic study of residential radon in Iowa that include 2726 outdoor and indoor measurements. Prediction of county-average radon is based on a geostatistical model for the radon data which assumes an underlying continuous spatial process. In the radon model, we account for uncertainties due to incomplete spatial coverage, spatial variability, characteristic differences between homes, and detector measurement error. The predicted radon averages are, in turn, included as a covariate in Poisson models for incident cases of acute lymphocytic (ALL), acute myelogenous (AML), chronic lymphocytic (CLL), and chronic myelogenous (CML) leukaemias reported to the Iowa cancer registry from 1973 to 2002. Since radon and leukaemia risk are modelled simultaneously in our approach, the resulting risk estimates accurately reflect uncertainties in the predicted radon exposure covariate. Posterior mean (95 per cent Bayesian credible interval) estimates of the relative risk associated with a 1 pCi/L increase in radon for ALL, AML, CLL, and CML are 0.91 (0.78-1.03), 1.01 (0.92-1.12), 1.06 (0.96-1.16), and 1.12 (0.98-1.27), respectively.

Epidemiology and outcomes research for MGUS, myeloma and amyloidosis

The epidemiology of plasma cell dyscrasias clearly links to a complicated multi-factorial pathogenic pathway that at the individual patient level gives no clear indication of why the malignant process has occurred but factors in the environment and within the genome give clues and are discussed. MGUS is a pre-malignant disorder characterised by monoclonal plasma cell proliferation in the bone marrow and no end-organ damage; the patients are asymptomatic. Primary amyloidosis is a rare disorder that is characterised by deposition of amyloid fibrils composed of immunoglobulin light chain fragments; symptoms relate to the affected organ. Multiple myeloma is a malignant disease of plasma cells and with improvements in treatment, patients can now expect a doubling of median survival to 5 years, a 20% chance of surviving >10 years and a 50% chance of complete remission (CR), morphological and biochemical. The challenge is now to determine exactly what this means to the individual myeloma patient in terms of benefit, and to society as a whole and this is the basis of 'outcomes research' which is discussed in this review.

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.

Cancer mortality in counties near two former nuclear materials processing facilities in Pennsylvania, 1950-1995

There has been concern that living near nuclear installations might increase the risk of cancer, including childhood leukemia, in surrounding communities. Such concern has been voiced by residents in Armstrong and Westmoreland Counties in Western Pennsylvania in conjunction with the operation of two former nuclear materials processing facilities located in the Apollo borough and the Parks township, just three miles apart. These facilities began operating in 1957 and 1960 and processed uranium and plutonium for commercial and naval applications. To evaluate the possibility of increased cancer rates in communities around the Apollo-Parks nuclear facilities, a cancer incidence and a cancer mortality survey were conducted. The county mortality findings are reported here. Nearly 40,000 cancer deaths occurred in the population residing in Armstrong and Westmoreland Counties from 1950 through 1995. Each of these two study counties was matched for comparison to three control counties in the same region on the basis of age, race, urbanization, and socioeconomic factors available from the 1990 U.S. Census. There were over 77,000 cancer deaths in the 6 control counties during the 45 y studied. Following similar methods used by the National Cancer Institute, Standardized Mortality Ratios (SMRs) were computed as the ratio of observed numbers of cancers in the study and control counties compared to the expected number derived from general population rates of the United States. Relative risks (RR) were computed as the ratios of the SMRs for the study and the control counties. There were no significant increases in the study counties for any cancer when comparisons were made with either the U.S. population or the control counties. In particular, deaths due to cancers of the lung, bone, liver, and kidney were not more frequent in the study counties than in the control counties. These are the cancers of a priori interest given that uranium and/or plutonium might be expected to concentrate in these tissues. Deaths from all cancers combined also were not increased in the study counties, and the RRs of cancer mortality before the facilities operated (1950-1964), during plant operations (1965-1980) and after plant closure (1980-1995) were similar: 0.96, 0.95 and 0.98, respectively. For childhood leukemia mortality, the relative risk comparing the study counties with their controls before plant start-up was 1.02, while during operations (RR 0.81) and after closure (RR 0.57) the relative risks were lower. The study is limited by the correlational approach and the relatively large size of the geographic areas of the counties studied.

Cancer risk around the nuclear power plants of Trillo and Zorita (Spain)

AIM

To investigate the association between cancer risk and proximity of place of residence to the Guadalajara nuclear power plants: Trillo and Zorita.

METHODS

Case-control study. Cases were patients admitted with cancer and controls were non-tumorous patients, both admitted to Guadalajara Hospital (period 1988-99). Exposure factor: place of residence (areas within 10, 20, and 30 km of each plant). Odds ratios (ORs) of those areas closest to the plants were calculated with respect to those furthest away; a linear trend analysis was also performed.

RESULTS

In the extreme areas in the vicinity of Trillo, an OR of 1.71 was obtained (95% CI 1.15 to 2.53), increasing in magnitude in the subgroup of more radioinducible tumours and in the period considered as post-latency (1997-99). Risk increased linearly with proximity to the two plants, significantly in Trillo (p < 0.01) but not in Zorita (p = 0.19).

CONCLUSIONS

There is an association between proximity of residence to Trillo and cancer risk, although the limitations of the study should be kept in mind when interpreting the possible causal relation.

Elevated childhood cancer incidence proximate to U.S. nuclear power plants

Numerous reports document elevated cancer rates among children living near nuclear facilities in various nations. Little research has examined U.S. rates near the nation's 103 operating reactors. This study determined that cancer incidence for children < 10 yr of age who live within 30 mi (48 km) of each of 14 nuclear plants in the eastern United States (49 counties with a population > 16.8 million) exceeds the national average. The excess 12.4% risk suggests that 1 in 9 cancers among children who reside near nuclear reactors is linked to radioactive emissions. If cancer incidence in 5 western states is used as a baseline, the ratio is closer to 1 in 5. Incidence is particularly elevated for leukemia. Childhood cancer mortality exceeds the national average in 7 of the 14 study areas.

Solid-tumor mortality in the vicinity of uranium cycle facilities and nuclear power plants in Spain

To ascertain solid tumor mortality in towns near Spain's four nuclear power plants and four nuclear fuel facilities from 1975 to 1993, we conducted a mortality study based on 12,245 cancer deaths in 283 towns situated within a 30-km radius of the above installations. As nonexposed areas, we used 275 towns lying within a 50- to 100-km radius of each installation, matched by population size and sociodemographic characteristics (income level, proportion of active population engaged in farming, proportion of unemployed, percentage of illiteracy, and province). Using log-linear models, we examined relative risk for each area and trends in risk with increasing proximity to an installation. The results reveal a pattern of solid-tumor mortality in the vicinity of uranium cycle facilities, basically characterized by excess lung [relative risk (RR) 1.12, 95% confidence interval (CI), 1.02-1.25] and renal cancer mortality (RR 1.37, 95% CI, 1.07-1.76). Besides the effects of natural radiation, these results could well be evincing the influence on public health exerted by the environmental impact of mining. No such well-defined pattern appeared in the vicinity of nuclear power plants. Monitoring of cancer incidence and mortality is recommended in areas surrounding nuclear fuel facilities and nuclear power plants, and more specific studies are called for in areas adjacent to installations that have been fully operational for longer periods. In this regard, it is important to use dosimetric information in all future studies.

Issues in the statistical analysis of small area health data

The availability of geographically indexed health and population data, with advances in computing, geographical information systems and statistical methodology, have opened the way for serious exploration of small area health statistics based on routine data. Such analyses may be used to address specific questions concerning health in relation to sources of pollution, to investigate clustering of disease or for hypothesis generation. We distinguish four types of analysis: disease mapping; geographic correlation studies; the assessment of risk in relation to a prespecified point or line source, and cluster detection and disease clustering. A general framework for the statistical analysis of small area studies will be considered. This framework assumes that populations at risk arise from inhomogeneous Poisson processes. Disease cases are then realizations of a thinned Poisson process where the risk of disease depends on the characteristics of the person, time and spatial location. Difficulties of analysis and interpretation due to data inaccuracies and aggregation will be addressed with particular reference to ecological bias and confounding. The use of errors-in-variables modelling in small area analyses will be discussed.

Leukaemia in the vicinity of two tritium-releasing nuclear facilities: a comparison of the Kruemmel Site, Germany, and the Savannah River Site, South Carolina, USA

In 1991, an increased rate of childhood leukaemia was reported from the small northern German community of Elbmarsch, which is located on the banks of the River Elbe opposite the Kruemmel nuclear power plant. Owing to the fact that the increase occurred six years after the start-up of the plant, radioactive discharges were suspected as being implicated in the development of the cases. Previous investigations have failed to identify any exposure which might be associated with the cluster. Nonetheless, concern regarding the increased tritium burden in the environment remains. To further assess the impact of tritium releases to the environment upon population cancer rates, the releases and leukaemia rates at the Savannah River site, USA, were compared with the Kruemmel site. Based on the data from 1991 to 1995, the incidence of childhood leukaemia in the vicinity of the Savannah River site was non-significantly less than expected compared with the significantly higher than expected rates close to the German plant. In contrast, tritium releases from the Savannah River site exceed those from the Kruemmel site by several orders of magnitude. The results of this observational study suggest that factors other than environmental tritium releases are associated with the increased number of leukaemia cases near the Kruemmel site.

Case-control isotonic regression for investigation of elevation in risk around a point source

Stone's isotonic regression method for analysing count data to estimate disease risk in relation to a point source of environmental pollution is now routinely used. This paper develops the corresponding procedure for case-control data consisting of the locations of individual cases with controls with associated covariate information. In this setting, the generalized likelihood ratio statistic to test the null hypothesis of constant risk against the alternative that risk is a monotone non-increasing function of distance from the point source is intractable. An approximate Monte Carlo test is described, extending an exact test proposed by Bithell for the situation in which there are no covariates. Interval estimates of risk as a function of distance from the point source are constructed by simulation of the sampling distribution of the isotonic regression estimator. The methodology is illustrated by two applications: one to the relative risk of larynx cancers and lung cancers near a now-disused industrial incinerator; the other to the risk of asthma in children in relation to distance of residence from the nearest main road.

Investigation of excess environmental risk around putative sources: Stone's test with covariate adjustment

Stone (Statistics in Medicine, 7, 649-660 (1988)) proposed a method of testing for elevation of disease risk around a point source. Stone's test is appropriate to data consisting of counts of the numbers of cases, Yi say, in each of n regions which can be ordered in increasing distance from a point source. The test assumes that the Yi are mutually independent Poisson variates, with means mu i = Ei lambda i where the Ei are the expected numbers of cases, for example based on appropriately standardized national incidence rates, and the lambda i are relative risks. The null hypothesis that the lambda i are constant is then tested against the alternative that they are monotone non-increasing with distance from the source. We propose an extension to Stone's test which allows for covariate adjustment via a log-linear model, mu i = Ei lambda i exp (sigma jp = 1 xij beta j), where the xij are the values of each of p explanatory variables in each of the n regions, and the beta j are unknown regression parameters. Our methods are illustrated using data on the incidence of stomach cancer near two municipal incinerators.

Geographical distribution of birth places of children with cancer in the UK

Using birth addresses, we examined the geographical variation in risk for all types of childhood cancers in the UK, on a scale corresponding to the 10-km squares of the National Grid. The effects of socioeconomic and environmental factors, including natural background radiation, were investigated and their relative importance assessed using Poisson regression. Data came from a national collection of all fatal cancers between 1953 and 1980 in children aged 0-15 years and consisted of 9363 children of known place of birth from 12 complete annual cohorts born in the period 1953-64. For solid cancers, as well as for leukaemias and lymphomas, there was marked variation of cumulative mortality according to place of birth. High mortalities were associated with areas characterized as having high social class, higher incomes and good housing conditions, but also with high population densities (births per hectare). Each of these contrasting social indicators operated independently of the other, indicating complex determining mechanisms. Mortalities increased with increased radon exposure, and the relationship operated independently of the socioeconomic factors. At this scale of analysis, we found no increased mortality in industrialized areas. A population-mixing infective hypothesis, which postulates high rates of leukaemia when highly exposed urban populations are introduced to isolated rural areas, was supported by observations of high mortalities in 'growth areas' and New Towns, but was not readily reconcilable with the high rates seen in the high-density areas. If these correlations do indeed represent an infective mechanism, then the outcomes are not limited to malignancies of the immune system alone.

The age peak in childhood acute lymphoblastic leukemia: exploring the potential relationship with socioeconomic status

BACKGROUND

White children have a much higher incidence rate of acute lymphoblastic leukemia (ALL) than do African American children. This discrepancy, coupled with the geographic and temporal variations in the incidence of childhood ALL, have led to speculation that factors associated with socioeconomic status (SES) may play an important role in its etiology. Because most of the variation is accounted for by the occurrence of a peak in incidence between the ages of 2 and 5 years, the purpose of this study was to compare the SES of children diagnosed with ALL between the peak ages of 2-5 years with those children diagnosed at other ages (birth-1 year and 6-14 years).

METHODS

Patients included 4210 children who were diagnosed with ALL between January 1, 1989 and December 31, 1991 by a member institution of the Children's Cancer Group or the Pediatric Oncology Group. Of these children, 3614 were white and 596 were African American. The SES of a case was defined as the SES of the child's zip code of residence at the time of diagnosis. Five sociodemographic variable categories for each zip code were obtained from the 1990 U.S. Census including per capita income, number of housing units by household income, number of housing units by level of urbanization, number of persons older than 25 years by educational attainment, and number of persons by occupation. Mean values were compared for white children versus African American children, and peak ages (2-5 years) versus nonpeak ages (birth-1 year and 6-14 years) for both whites and African Americans. In addition, Wilcoxon's rank sum tests were performed.

RESULTS

There were statistically significant differences between the means in each of the socioeconomic categories when African Americans were compared with whites. However, within race, the means of the SES variables for white children diagnosed during the peak ages (2-5 years) were not significantly different from children diagnosed at other ages (birth-1 year and 6-14 years). Similarly, all but one of the comparisons for African American children yielded nonstatistically significant results. Similar results were obtained from the Wilcoxon's rank sum tests.

CONCLUSIONS

The results of this analysis suggest that age differences in childhood ALL incidence may not be solely accounted for by SES differences.

Hazard proximities of childhood cancers in Great Britain from 1953-80

STUDY OBJECTIVES

Firstly, to examine relationships between the birth and death addresses of children dying from leukaemia and cancer in Great Britain, and the sites of potential environmental hazards; and secondly to measure relative case densities close to, and at increasing distances from, different hazard types.

DESIGN

Home address postcodes (PCs) and their map coordinates were identified at birth and at death in children who died from leukaemia or cancer. Potentially hazardous industrial addresses and PCs were listed from business and other directories, and map coordinates obtained from the Central Postcode Directory or else located directly on Ordnance Survey (OS) maps. Railway lines and motorways were digitised from OS maps. Numbers of deaths (and births) at successive radial distances from these hazards were counted and compared with expected numbers. The latter were based on a count of all PCs at similar distances. Relative case density ratios at successive distances from the hazards were obtained from observed and expected numbers, aggregated over similar sites. This was repeated for different hazard types and results were tested for evidence of systematic centrifugal case density gradients.

PARTICIPANTS AND SETTING

All 22,458 children dying from leukaemia or cancer aged 0-15 years, in England, Wales, and Scotland, between 1953 and 1980.

MAIN RESULTS

Relative excesses of leukaemias and of solid cancers were found near the following: (1) oil refineries, major oil storage installations, railside oil distribution terminals and factories making bitumen products; (2) motor car factories, coach builders, and car body repairers; (3) major users of petroleum products including manufacturers of solvents, paint sprayers, fibreglass fabricators, paint and varnish makers, plastics and detergent manufacturers, and galvanisers; (4) users of kilns and furnaces including steelworks, power stations, galvanisers, cement makers, brickworks, crematoria and aluminium, zinc, and iron/steel foundries; (5) airfields, railways, motorways and harbours. The findings for leukaemias and for solid cancers were indistinguishable. The hazard proximities of birth addresses were stronger than for death addresses. For children who had moved house between birth and death, the proximity effect was limited to the birth addresses.

CONCLUSIONS

Childhood cancers are geographically associated with two main types of industrial atmospheric effluent namely: (1) petroleum derived volatiles and (2) kiln and furnace smoke and gases, and effluents from internal combustion engines.

Adult leukemia and proximity-based surrogates for exposure to Pilgrim plant's nuclear emissions

Possible associations between adult leukemia incidence and proximity-based surrogate measures of potential for exposure to radioactive emissions from the Pilgrim nuclear power plant in Plymouth, Massachusetts, were investigated. Included in this study were 105 nonchronic lymphocytic leukemia cases, diagnosed between 1978 and 1986 at age 13 y or older, that occurred in 22 towns near Pilgrim; population controls numbered 208. Residence within 4 mi (6.4 km) of Pilgrim during "high-emissions" years was related to case-control status (adjusted odds ratio [OR] = 3.88, 95% confidence interval [95% CI] = 0.81-10.64). A high "exposure" score (i.e., a value that accounted for downwind time) was also related to case-control status (OR = 3.46, 95% CI = 1.50-7.96). Some statistically significant dose-response trends were found. Cautious interpretation of associations is warranted in light of the low levels of reported emissions.

Cancer mortality around French nuclear sites

This study was designed to investigate cancer mortality in the population aged 0 to 64 years residing around the 13 main French nuclear sites in operation before 1985. Five hundred and three communes located within 16 km of the installation were identified and their populations were followed from 1968 to 1989. A total of 8,970,000 person-years of observation was accumulated. The number of cancer deaths and the number of deaths for cancers possibly related to radiation observed in these communes were compared to national mortality rates. There was no difference in overall cancer mortality or in the risk of mortality by cancer site except for breast cancer, for which a deficit was observed in the vicinity of nuclear sites. After correction for the multiplicity of tests, this difference was not significant. Our study showed no excess cancer mortality in the population aged 0 to 64 years residing around French nuclear sites.

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.

The power of focused tests to detect disease clustering

Statistical tests have been proposed for determining whether incident cases of adverse health effects are 'clustered' together. Several procedures, termed 'focused', specifically analyse disease surveillance data around pre-specified putative sources of environmental hazard. Little has been done to compare the performance of various proposed methods on actual models of clustering. Analytic power functions are derived for three tests of focused clustering. These functions are based on the probabilistic structure of the clustering tests and do not require simulation. The three tests are compared with respect to statistical power on hypothetical data where monotone multiplicative increases in disease risk near a putative hazard define disease clusters of varying intensity.

MCMC methods for putative pollution source problems in environmental epidemiology

This paper demonstrates the use of the Gibbs Sampler and other Markov Chain Monte Carlo (MCMC) methods in two applications in environmental epidemiology. The first example concerns the application of a Metropolis-Hastings/Gibbs sampler to a Cox process with a direction-dependent cluster variance parameter. The second example consists of the estimation of the posterior (spatial) distribution of a putative location.

Incidence of leukaemia in young people around the La Hague nuclear waste reprocessing plant: a sensitivity analysis

The objectives are to investigate the incidence of childhood leukaemia in young people around the French nuclear waste reprocessing plant (La Hague, Normandy) for the period 1978-1992, and to check the sensitivity of the results to the choice of disease clustering tests and reference rates. The performance of three statistical procedures are compared: a conventional approach; a Poisson maximum test, and an extraction mapping technique. On the whole, the results are in general agreement and demonstrate the apparent existence of a distinct cluster of childhood leukaemia, contiguous and south-east of the La Hague nuclear facility.

Spatial statistical methods in environmental epidemiology: a critique

Despite recent advances in the available statistical methods for geographical analysis, there are many constraints to their application in environmental epidemiology. These include problems of data availability and quality, especially the lack in most situations of environmental exposure measurements. Methods for disease 'cluster' investigation, point source exposures, small-area disease mapping and ecological correlation studies are critically reviewed, with the emphasis on practical applications and epidemiological interpretation. It is shown that, unless dealing with rare diseases, high specificity exposures and high relative risks, cluster investigation is unlikely to be fruitful, and is often complicated by the post hoc nature of such studies. However, it is recognized that in these circumstances proper assessment of the available data is often required as part of the public health response. Newly available methods, particularly in Bayesian statistics, offer an appropriate framework for geographical analysis and disease mapping. Again, it is uncertain whether they will give important clues as to aetiology, although they do give valuable description. Perhaps the most satisfactory approach is to test a priori hypotheses using a geographical database, although problems of interpretation remain.

Childhood leukaemia and non-Hodgkin's lymphoma near large rural construction sites, with a comparison with Sellafield nuclear site

OBJECTIVE

To determine whether population mixing produced by large, non-nuclear construction projects in rural areas is associated with an increase in childhood leukaemia and non-Hodgkin's lymphoma.

DESIGN

A study of the incidence of leukaemia and non-Hodgkin's lymphoma among children living near large construction projects in Britain since 1945, situated more than 20 km from a population centre, involving a workforce of more than 1000, and built over three or more calendar years. For periods before 1962 mortality was studied.

SETTING

Areas within 10 km of relevant sites, and the highland counties of Scotland with many hydroelectric schemes.

SUBJECTS

Children aged under 15.

RESULTS

A 37% excess of leukaemia and non-Hodgkin's lymphoma at 0-14 years of age was recorded during construction and the following calendar year. The excesses were greater at times when construction workers and operating staff overlapped (72%), particularly in areas of relatively high social class. For several sites the excesses were similar to or greater than that near the nuclear site of Sellafield (67%), which is distinctive in its large workforce with many construction workers. Seascale, near Sellafield, with a ninefold increase had an unusually high proportion of residents in social class I. The only study parish of comparable social class also showed a significant excess, with a confidence interval that included the Seascale excess.

CONCLUSION

The findings support the infection hypothesis and reinforce the view that the excess of childhood leukaemia and non-Hodgkin's lymphoma near Sellafield has a similar explanation.

Leukaemia mortality around French nuclear sites

This study was designed to investigate leukaemia mortality in the population under the age of 25 residing around the 13 French nuclear sites operating in 1985. In four geographical zones defined according to the distance from the site, 503 exposed communes were identified and followed up between 1968 and 1989. A total of 4,132,000 person-years of observation were accumulated. The number of leukaemia deaths observed (69) did not differ from the expected number (86.15) estimated according to national mortality statistics. There was no difference in the risks of leukaemia mortality according to sex, age, type of installation and no trend with an increasing distance from installations.

Detection and assessment of clusters of disease: an application to nuclear power plant facilities and childhood leukaemia in Sweden

We review some recent statistical methods for examining geographic patterns of disease incidence for the presence of clusters. General methods search for clusters throughout the study area and then assess the statistical significance of any clusters detected. Focused methods check for elevated incidence rates close to prespecified locations of putative sources of hazard. We apply the methods to leukaemia incidence data for children aged 0-15 years in Sweden (1980-1990), particularly in reference to locations of nuclear power facilities. Unlike some other studies, notably in the United Kingdom, we do not find any significant clusters.

Distribution of childhood leukaemias and non-Hodgkin's lymphomas near nuclear installations in England and Wales

OBJECTIVE

To examine the relation between the risk of childhood leukaemia and non-Hodgkin's lymphoma and proximity of residence to nuclear installations in England and Wales.

DESIGN

Observed and expected numbers of cases were calculated and analysed by standard methods based on ratios of observed to expected counts and by a new statistical test, the linear risk score test, based on ranks and designed to be sensitive to excess incidence in close proximity to a putative source of risk.

SETTING

Electoral wards within 25 km of 23 nuclear installations and six control sites that had been investigated for suitability for generating stations but never used.

SUBJECTS

Children below age 15 in England and Wales, 1966-87.

MAIN OUTCOME MEASURE

Registration of any leukaemia or non-Hodgkin's lymphoma.

RESULTS

In none of the 25 km circles around the installations was the incidence ratio significantly greater than 1.0. The only significant results for the linear risk score test were for Sellafield (P = 0.00002) and Burghfield (P = 0.031). The circles for Aldermaston and Burghfield overlap; the incidence ratio was 1.10 in each. One of the control sites gave a significant linear risk score test result (P = 0.020). All the tests carried out were one sided with P values estimated by simulation.

CONCLUSION

There is no evidence of a general increase of childhood leukaemia or non-Hodgkin's lymphoma around nuclear installations. Apart from Sellafield, the evidence for distance related risk is very weak.

The effects of scale on tests for disease clustering

Surveillance of a large geographic region for 'clusters' of adverse health events, particularly cancers, often involves searching for raised incidence in the vicinity of prespecified putative sources of hazard. For reasons of practicality or of confidentiality, incidence and population data are usually only available aggregated over subregions or 'cells'. The performance of statistical procedures designed to detect the presence of clusters can be highly sensitive to the level of aggregation, that is to the choice of partition of the region into the cells. We investigate this sensitivity in the cases of three recently proposed procedures, namely those of Besag and Newell, Stone, and Waller et al. For illustration, we use leukaemia incidence data for 1978-82 in a region of upstate New York, with inactive hazardous waste sites containing trichloroethylene acting as suspected sources.

[Routine analysis of public health surveillance data: which statistical procedures to use?]

In recent years an increasing interest in epidemiological surveillance (that we prefer to label public health surveillance) has emerged. The viewpoint that the ease of access to computers and statistical software may permit the use of more sophisticated statistical methodologies in the analysis of surveillance data has been profounded in many studies. It is a cause of concern that this attitude, when used indiscriminated by, may lead to analysis lacking in theoretical support. Thus, first, a viewpoint about surveillance in public health is presented and the basic propositions of the theory of statistical hypothesis tests and interval estimation are described briefly and without technicalities. The nature of surveillance data, their nonsampling character and non-random selection are also commented on. Some descriptive procedures that may be used without loss of quality in analysis are described than some procedures that are proposed in the relevant international literature but that need fuller investigation before being introduced in routine data analysis are given.

Cancer in Cumbria and in the vicinity of the Sellafield nuclear installation, 1963-90

OBJECTIVE

To reappraise the epidemiological findings reported by the Black Advisory Group concerning a possible excess of malignant disease, particularly of childhood acute lymphoid leukaemia and non-Hodgkin lymphomas, in the vicinity of the Sellafield nuclear installation, and to determine whether any excess of malignant disease had occurred among people aged 0-24 years in the area in the years after the Black report--that is, from 1984 to 1990.

DESIGN

Calculation of incidence of cancer using data from population based cancer registries and special surveys.

SETTING

England and Wales; county of Cumbria; county districts Allerdale and Copeland within Cumbria; Seascale ward within Copeland.

SUBJECTS

All residents under the age of 75 years in the above areas, but with particular reference to those aged 0-24 years.

MAIN OUTCOME MEASURES

Numbers of cases and incidence particularly of lymphoid leukaemia and non-Hodgkin lymphomas in those aged 0-24 years, but including other cancers and age groups.

RESULTS

Previous reports of an increased incidence of cancer, especially of leukaemia, among those aged 0-24 years in Seascale during the period up to and including 1983 are confirmed. During 1984-90 there was an excess of total cancer among those aged 0-24 years. This was based on four cases including two cases of non-Hodgkin lymphoma but none of leukaemia. There was an increased, but nonsignificant, incidence of other cancers, based on two cases (one pinealoma and one Hodgkin's disease) occurring among those aged 15-24 years during 1984-90. This was not observed in the younger age group or in previous years. For the immediately surrounding area--that is, the county districts of Allerdale and Copeland excluding Seascale and in the remainder of Cumbria--there was no evidence of an increased incidence of cancer among those aged 0-24 years in either period.

CONCLUSIONS

During 1963-83 and 1984-90 the incidence of malignant disease, particularly lymphoid leukaemia and non-Hodgkin lymphomas, in young people aged 0-24 in Seascale was higher than would be expected on the basis of either national rates or those for the surrounding areas. Although this increased risk is unlikely to be due to chance, the reasons for it are still unknown.

Viruses, clusters and clustering of childhood leukaemia: a new perspective?

Clusters of childhood leukaemia have, during a lengthy and controversial history, focussed attention on two alternative putative aetiological agents: infections and localised environmental pollution. In the United Kingdom emphasis is currently placed on the latter because of reports of localised clusters in the vicinity of two nuclear reprocessing plants. Now the most recent studies of spatial clustering in the United Kingdom also support the hypothesis that a substantial population of cases of childhood acute lymphoblastic leukaemia (ALL) arise as a rare host response to certain patterns of exposure to common infectious agents--the aberrant response model. Relevant aspects of the epidemiology of ALL are reviewed from this perspective and the hypothesis shown to be capable of unifying reported associations with different types of risk factor. It is probable that specific agent(s) are involved though none have been identified and these may share many epidemiological characteristics of herpes viruses. The possible relevance of these results to associations with prenatal parental occupational exposures to dusts and ionising radiation is explored.

Childhood leukemia in the vicinity of Canadian nuclear facilities

An ecologic study was conducted to determine whether leukemia rates among children born to mothers residing in the vicinity of Ontario (Canada) nuclear facilities differed from the provincial average. Childhood leukemia mortality and incidence ratios for the period 1950 to 1987 were examined for five regions within 25 km of a nuclear facility. The nuclear facilities included a research development facility, a uranium refinery, a uranium mining and milling facility, and two nuclear-power generating stations. Overall, the observed number of leukemia deaths (O = 54) was slightly greater than expected (E = 46.1) during the period when the facilities operated, but the difference was not statistically significant (O/E = 1.17, 95 percent confidence interval [CI] = 0.88-1.53). There was no indication of a birth cohort effect, as the mortality ratios based on place of birth were not significantly greater than the mortality ratios based on place of death. In the analyses of individual facilities, CIs included the null value and were generally wide because of the small observed and expected numbers; however, in the vicinity of the nuclear generating stations, the observed relative excess of leukemia deaths (O = 36, O/E = 1.40) had a lower confidence limit that was close to the null value.

Chronic leukaemias

In recent years many subtypes of CLL and some CML variants have been recognized throughout the world by means of careful clinical, epidemiological, immunological, molecular biological and viral studies. Most striking has been the establishment of a close association between certain immunophenotypical subtypes of CLL and infection with HTLV-I and possibly HTLV-II. CLL has consistently been shown to have a strong genetic component and a low incidence among Asians, but a growing body of evidence also links this major leukaemia type with environmental factors including solvents, unidentified farming and other occupational exposures. In contrast, CML is characterized by few genetic associations, relatively homogenous world-wide distribution, greater frequency in Blacks than in Whites, little evidence of viral aetiology, and evidence that exposures to ionizing radiation, benzene and possibly other chemical agents are important aetiological factors. Most studies suggest that acquired rather than genetic factors are of greater importance in the aetiology of CML, but this conclusion is somewhat difficult to reconcile with the relatively small variation in incidence rates internationally. Common to both disorders in most populations are an increasing incidence with age, male predominance, and stability of incidence, survival and mortality over the years, exclusive of improved survival of CML following allogeneic bone marrow transplantation.

Problems in the interpretation of small area analysis of epidemiological data: the case of cancer incidence in the West of Scotland

STUDY OBJECTIVE

The aim was to examine the extent to which random variation alone will produce differences in observed incidence rates between small areas which will affect measures of spatial clustering and estimates of relative risk.

DESIGN

This was a study of changes in the pattern of spatial concentration of cancer incidence over a five year time period. A comparison was made of observed incidence rates for 34 tumour sites with randomly generated values and, where possible, with expected values derived from known relative risks.

SETTING

Twenty six local government districts in the West of Scotland.

MAIN RESULTS

A statistically significant relationship was observed between sample size and the stability of a summary measure of spatial concentration. Almost all observed highest:mean rate ratios were within the 95% confidence interval of the simulated distribution of these values. In three cases examined, both observed and simulated highest:lowest rate ratios were larger than those expected on the basis of known exposures to risk.

CONCLUSIONS

In the absence of a prior hypothesis, small area analysis of epidemiological data for periods of less than 10 years will almost always give misleading results for all but the most common diseases.

Current concepts on monoclonal gammopathies

This is a review of the monoclonal gammopathies, including a discussion of cause. The role of T lymphocytes and B lymphocytes is presented. The recognition of a monoclonal protein in the serum and urine is presented in detail. The frequency of benign and malignant monoclonal gammopathies is provided. A long-term follow-up of 241 patients with apparently benign monoclonal gammopathy is examined closely. In this series, multiple myeloma, macroglobulinaemia, amyloidosis, or related disorders developed in 22% of the 241 patients with long-term disease. The median duration from the recognition of the monoclonal protein until the development of serious disease was approximately eight to ten years. The differentiation of benign from malignant monoclonal gammopathies is examined in detail. The point is made that patients must be followed indefinitely because malignancy may develop more than 20 years later. The association of monoclonal gammopathies with other apparently unrelated diseases is discussed.