The relationship of incidence of childhood lymphoblastic leukaemia to social class

Parental Occupation and Other Environmental Factors in the Etiology of Leukemias and Non-Hodgkin'S Lymphomas in Childhood: A Case-Control Study

We report the results of a hospital-based, case-control study on acute lymphocytic leukemia (ALL), acute non-lympocytic leukemia (AnLL) and non-Hodgkin lymphoma (NHL) in childhood. The study was conducted from 1981 to 1984 in Turin (Italy). One hundred and forty-two children with ALL, 22 with AnLL and 19 with NHL were included, as well as 307 controls. Information on parental smoking habits, parental occupation, ionizing radiation and childhood diseases were collected using a standard questionnaire during a personal interview of the relative attending the child in the hospital. The odds ratios for antenatal diagnostic radiation were 1.1 (NS) for ALL and 2.4 (NS) for AnLL. No association was found with diseases in childhood. Paternal and maternal smoking habits were similar for ALL cases and controls. Both maternal and paternal smoking were associated with NHL: for paternal smoking, odds ratios were around 5, but without a correlation with number of cigarettes. Positive associations observed with maternal employment were: ALL with teacher and cleaner; AnLL and textile worker; NHL and baker. Corresponding association with paternal jobs were: ALL with clerks, farmers and employment in office equipment production; AnLL and workers in building, tire or textile industries; NHL and lorry drivers, workers in the building or in the wood and furniture industry.

Animal Models for the Study of Childhood Leukemia: Considerations for Model Identification and Optimization to Identify Potential Risk Factors

Leukemias are the most common pediatric malignancies diagnosed in western industrialized societies. In spite of the substantial incidence of childhood leukemia in the United States and other countries, neither epidemiology studies conducted in human populations nor hazard identification studies conducted using traditional animal models have identified environmental or other factors that are directly linked to increased risk of disease. Molecular biology data and mathematical modeling of incidence patterns suggest that pediatric leukemogenesis may occur through a multistage or “multihit” mechanism that involves both in utero and postnatal events. The authors propose that pediatric leukemias can be modeled experimentally using a “multihit” paradigm analogous to the “initiation-promotion” and “complete carcinogenesis” models developed for tumor induction in mouse skin and rat liver. In this model for childhood leukemia, an initial genetic alteration occurs during in utero or early postnatal development, but clinical disease develops only upon additional genetic or nongenetic events that occur during the postnatal period. Application of this multistage or “multihit” model to hazard assessment studies conducted in transgenic or knockout mice carrying relevant molecular lesions may provide a sensitive approach to the identification of environmental agents that are important risk factors for childhood leukemia.

Dangers associated with civil nuclear power programmes: weaponization and nuclear waste

The number of nuclear power plants in the world rose exponentially to 420 by 1990 and peaked at 438 in 2002; but by 2014, as closed plants were not replaced, there were just 388. In spite of using more renewable energy, the world still relies on fossil fuels, but some countries plan to develop new nuclear programmes. Spent nuclear fuel, one of the most dangerous and toxic materials known, can be reprocessed into fresh fuel or into weapons-grade materials, and generates large amounts of highly active waste. This article reviews available literature on government and industry websites and from independent analysts on world energy production, the aspirations of the 'new nuclear build' programmes in China and the UK, and the difficulties in keeping the environment safe over an immense timescale while minimizing adverse health impacts and production of greenhouse gases, and preventing weaponization by non-nuclear-weapons states acquiring civil nuclear technology.

Area-based differentials in childhood cancer incidence in Australia, 1996-2006

BACKGROUND

International studies examining the association between the incidence of childhood cancer and characteristics of the area in which the patient lives have generally reported inconsistent patterns. Area-based differentials in childhood cancer throughout Australia have not been previously published at a national level.

PROCEDURE

Population-based information from the Australian Paediatric Cancer Registry was used to identify all children aged 0- to 14-years old diagnosed with invasive cancer or intracranial and intraspinal tumors of benign or uncertain behavior between 1996 and 2006. Age-standardized incidence rates per million children per year and the corresponding incidence rate ratios were calculated, categorized by remoteness of residence and an area-based index of socioeconomic disadvantage. Results were also stratified by the most common types of childhood cancer.

RESULTS

There was a significant, decreasing gradient in the incidence of childhood cancer as remoteness of residence increased. Children living in remote or very remote areas were 21% less likely to be diagnosed with cancer compared to children in major cities, mainly due to differences in the incidence of leukemias and lymphomas. This differential was no longer significant when only non-Indigenous children were considered. No clear relationship was found between incidence and socioeconomic status (SES) in contrast to similar earlier studies.

CONCLUSIONS

The findings by remoteness of residence are consistent with the lower incidence rates of cancer that are typically associated with Indigenous Australians. There is also a suggestion that the etiological factors associated with childhood leukemia and SES may have altered over time.

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.

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.

Parental Occupational Exposure and the Risk of Acute Lymphoblastic Leukemia in Offspring in Israel

OBJECTIVE

Parental employment in occupations that have potential exposures to organic solvents or pesticides could be associated with the risk of childhood acute lymphoblastic leukemia (ALL) in their offspring.

METHODS

We explored this hypothesis by studying the association with respect to exposure time windows. Our case-control study included 224 children, 112 diagnosed with ALL and 112 matched controls.

RESULTS

A significantly higher odds ratio (OR) was found between childhood ALL and reported parental occupational exposures. Analysis of exposures of both parents by exposure time windows revealed significant OR during the preconception and postnatal periods separately.

CONCLUSIONS

The results provide support to the association between parental occupational exposures and ALL in their children. These results should be interpreted cautiously because of the small numbers, biases characterizing case-control studies, and the use of hospital-based controls.

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.

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.

Nongenetic causes of childhood cancers: evidence from international variation, time trends, and risk factor studies

Ionizing radiation and a variety of genetic conditions are thought to explain 5-10% of childhood cancers. Infection with Epstein-Barr virus (EBV) in parts of Africa and human immunodeficiency virus (HIV) increase the risk of Burkitt's lymphoma and Kaposi's sarcoma, respectively. Other risk factors have not been conclusively identified. A review of the data on international variation in incidence, recent changes in incidence, and risk factors suggests that many childhood cancers are likely to have nongenetic causes. The pattern of international variation and associations with surrogates of infection suggest an infectious etiology for acute lymphoblastic leukemia, although no agent has been identified. The biologic plausibility is strong that maternal consumption of food containing DNA topoisomerase II inhibitors may increase the risk of acute myeloid leukemia, although the data are limited now. For brain tumors, cured meats, polyomaviruses, and farm exposures may have etiologic roles. Changes in the incidence and characteristics of children with hepatoblastoma as well as risk factor studies suggest a role for an exposure of very low birth weight babies. High birth weight, tea or coffee consumption, and certain paternal occupations have shown some consistency in their association with Wilms' tumor. For most of the other cancers, very few epidemiologic studies have been conducted, so it is not surprising that nongenetic risk factors have not been detected. The most important difference between the cancers for which there are good etiologic clues and those for which there are not may be the number of relevant studies.

Childhood leukemia and road traffic: A population-based case-control study

To assess the effect of road traffic exhaust on the risk of childhood leukemia, we carried out a population-based case-control study in the Province of Varese, northern Italy, covered by a population-based cancer registry. All 120 incident cases from 1978-97 were included in the study. Four controls per case, matched by age and gender, were sampled from population files. As index of exposure to traffic exhaust we estimated the annual mean concentration of benzene outside the home using a Gaussian diffusion model. This model uses traffic density (vehicles/day) on nearby main roads, distance between roads and residence, and information on vehicle emissions and weather conditions to estimate benzene concentration. Compared to children whose homes was not exposed to road traffic emissions (<0.1 microg/m(3) of benzene as estimated by the model), the risk of childhood leukemia was significantly higher (relative risk [RR] = 3.91; 95% confidence interval [CI] = 1.36-11.27) for heavily exposed children (over 10 microg/m(3) estimated annual average). For the intermediate exposure group (0.1-10 microg/m(3)) the relative risk was 1.51 (95% CI = 0.91-2.51). These data, considered with other available evidence, suggest that motor traffic emissions can be involved in the etiology of childhood leukemia.

Is the timing of exposure to infection a major determinant of acute lymphoblastic leukaemia in Hong Kong?

The hypothesis that protection of infants from exposure to infectious agents with delayed first exposure to one or more specific agents together contribute to the aetiology of childhood leukaemia, especially common acute lymphoblastic leukaemia (cALL), has substantial indirect support from descriptive epidemiology and case-control studies in developed Western countries. A case-control study of childhood leukaemia diagnosed at ages 2-14 years has now been conducted in Hong Kong. Cases (n=98) formed a consecutive series of Chinese children diagnosed with acute leukaemia; controls (n=228) were identified following a survey using random digit dialling and required to attend for medical examination by a paediatrician. Interviews with mothers were conducted in hospital by one trained interviewer using a structured questionnaire. Odds ratios (OR) and 95% confidence intervals (CI) are reported for exposure variables capable of serving as proxies for exposure to infection in two critical time periods: first year of life, year before reference date (diagnosis for cases, corresponding date for controls). Analyses used logistic regression with adjustment for appropriate confounders. Change of area of residence reduced risk if during the first time period (OR = 0.47 [95% CI 0.23, 0.98]) and increased risk if during the second (OR=3.92, [95% CI 1.47, 10.46]). Reported roseola and/or fever and rash in the first year of life reduced risk (OR=0.33 [95% CI 0.16, 0.68]) whereas tonsillitis in the period 3-12 months before reference date increased risk (OR=2.56 [95% CI 1.22, 5.38]). Some other proxies for exposure to infection at the critical times were associated with predicted patterns of risk but day-care attendance failed to show predicted associations. These results provide support for the delayed exposure hypothesis in an affluent geographical setting in which population exposure to infectious agents is quite distinct from the settings of previous case-control studies.

Association of early life factors and acute lymphoblastic leukaemia in childhood: historical cohort study

In a historical cohort study of all singleton live births in Northern Ireland from 1971-86 (n=434,933) associations between early life factors and childhood acute lymphoblastic leukaemia were investigated. Multivariable analyses showed a positive association between high paternal age (> or =35 years) and acute lymphoblastic leukaemia (relative risk=1.49; 95% confidence interval (CI)=0.96--2.31) but no association with maternal age. High birth weight (> or =3500 g) was positively associated with acute lymphoblastic leukaemia (relative risk=1.66; 95% CI=1.18--2.33). Children of mothers with a previous miscarriage or increased gestation (> or =40 weeks) had reduced risks of ALL (respective relative risks=0.49; 95% CI=0.29--0.80, and 0.67; 95% CI=0.48--0.94). Children born into more crowded households (> or =1 person per room) had substantially lower risks than children born into less crowded homes with also some evidence of a lower risk for children born into homes with three adults (relative risks=0.56; 95% CI=0.35-0.91 and 0.58; 95% CI=0.21-1.61 respectively). These findings indicate that several early life factors, including living conditions in childhood and maternal miscarriage history, influence risk of acute lymphoblastic leukaemia in childhood.

Historical evidence that residential electrification caused the emergence of the childhood leukemia peak

A peak in childhood leukemia, ages two through four, emerged de novo in the 1920s in the United Kingdom and slightly later in the United States (US). Electrification in US farm and rural areas lagged behind urban areas until 1956. In recent years, childhood leukemia has been associated with residential electromagnetic fields. During 1928-1932, in states with above 75% of residences served by electricity, leukemia mortality increased with age for single years 0-4, while states with electrification levels below 75% showed a decreasing trend with age (P = 0.009). During 1949-1951, all states showed a peak in leukemia mortality at ages 2-4. At ages 0-1, leukemia mortality was not related to electrification levels. At ages 2-4, there was a 24% (95% confidence interval (CI), 8%-41%) increase in leukemia mortality for a 10% increase in percent of homes served by electricity. The childhood leukemia peak of common acute lymphoblastic leukemia may be attributable to electrification.

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

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

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.

Birth characteristics, sibling patterns, and acute leukemia risk in childhood: a population-based cohort study

BACKGROUND

The occurrence of acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) during childhood may be influenced by factors operating in fetal life. Furthermore, childhood ALL has been suggested to be linked to patterns of infection during infancy.

PURPOSE

To explore these hypotheses and other associations, we studied the impact of sibling patterns (e.g., birth order) and birth characteristics (e.g., birth weight) on the risk of childhood ALL and AML.

METHODS

By linkage of records of population-based registries, a cohort of all children whose mothers were born in Denmark from April 1935 through March 1978 was established. Children who developed ALL or AML during the period from April 1968 through December 1992 were identified by linkage with the Danish Cancer Registry. Birth weights were obtained for children born during the period from January 1973 through December 1992 by linkage with the Medical Birth Registry.

RESULTS

The cohort of approximately 2.0 million children was followed for the diagnosis of ALL or AML for 20.9 million person-years. A total of 704 cases of childhood ALL were identified. Among 0-4 year olds, the relative risks (RRs) of ALL for birth order positions 1, 2, 3, and 4+ were 1.00 (reference), 0.85 (95% confidence interval [CI] = 0.68-1.07), 0.91 (95% CI = 0.66-1.25), and 0.57 (95% CI = 0.30-1.06), respectively (P for trend = .09). A decreasing trend was not observed among 5-14 year olds. A significant log-linear association between birth weight and the risk of ALL was observed for both age groups. Overall, the RR of ALL increased by a factor of 1.46 (95% CI = 1.18-1.81) (P = .0005) for each kilogram of increase in birth weight. A total of 114 cases of childhood AML were identified. Children born second or later in the birth order had an increased risk of AML (RR = 1.53; 95% CI = 1.01-2.32) compared with firstborns. A particularly high risk of AML at ages 2 (RR = 2.53; 95% CI = 1.46-4.40) and 3 years was associated with having siblings compared with being an only child at those ages. Similar to the findings for ALL risk, there was a significant association between birth weight and AML risk. The relative increase in AML risk per 1-kg increase in birth weight was 2.14 (95% CI = 1.19-3.85; P = .009).

CONCLUSION AND IMPLICATIONS

The association between birth weight and childhood leukemia suggests the importance of intrauterine factors. A plausible explanation may be that increasing birth weight is associated with a higher rate of cell proliferation and/or a larger number of precursor cells being at risk of malignant transformation. The inverse association between birth order and ALL risk among 0-4 year olds was weak, but it was compatible with the hypothesis that delayed exposure to infection may increase the risk of ALL in this age group. The association of childhood AML with birth order and sibship size at young ages deserves further attention in the search for environmental factors that affect childhood AML risk.

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.

Evaluating the relationships among maternal reproductive history, birth characteristics, and infant leukemia: a report from the Children's Cancer Group

PURPOSE

Specific events in the mother's reproductive history and certain birth characteristics have been associated with childhood leukemia. Few studies have explored these associations specifically in infants.

METHODS

The Children's Cancer Group (CCG) conducted three separate case-control studies of childhood leukemia that involved similar methodologies and data collection. Data from interviews of the mothers of a total of 303 children diagnosed with leukemia at 1 year of age or younger and their matched controls (n = 468) were available from the three studies. These data included maternal reproductive history (stillbirths, abortions, and miscarriages) and certain birth characteristics of the index child.

RESULTS

Compared with controls, cases were significantly more likely to be female (P < 0.01) and were more often heavier at birth (particularly cases diagnosed after 6 months of age (odds ratio, 4.18; 95% confidence interval, 1.75-10.02)). Overall, there were no statistically significant differences between cases and controls in regard to maternal report of any type of previous fetal loss. Finally, being a later-born child was associated with an increased risk of acute myeloid leukemia but not of acute lymphoblastic leukemia.

CONCLUSIONS

The relationships among birthweight, prior fetal loss, and risk of infant leukemia appear to be complex. Further studies of infant leukemia that incorporate molecular as well as epidemiologic data may help to elucidate these differences.

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.

Characterization of acute lymphoblastic leukemia subtypes in Brazilian patients

The distribution of the acute lymphoblastic leukemia (ALL) subsets in 225 consecutive Brazilian patients was determined by an immunophenotypic study with an extensive panel of monoclonal antibodies. All subsets were detected and their relative frequencies were similar to those described in developed countries, except for the B-mature subset which had a higher frequency, especially in adults. Associated myeloid markers were expressed by 11% of the ALL and CD10 by 15.9% of T-ALL cases. Besides, the incidence rates determined for the region of Ribeirão Preto showed that the overall incidence of ALL was 12.5 cases/10(6) people years (PY) (5 cases/10(6) PY in non-Whites versus 14 cases/10(6) PY in Whites); the incidence of childhood ALL was 25.5 cases/10(6) PY (8.1 versus 29.8 cases/10(6) PY in non-Whites and Whites, respectively) and the incidence of ALL in adults was 6.2 cases/10(6) PY (5.5 versus 6.1 cases/10(6) Py in non-Whites and Whites, respectively). The significantly lower incidence rate of ALL in non-White children was associated with a selective deficit of the common subtype and a lack of the typical age peak of incidence in this group. The ALL features demonstrated here in Brazilian non-White children resemble those described in the American non-Whites before the seventies and those in British and American Whites at the beginning of the century.

Childhood cancer incidence in Australia, 1982-1991

The data of the Australian Paediatric Cancer Registry on childhood cancer incidence in Australia for the 10-year period 1982-1991 are presented. The crude average annual incidence of cancer in children under the age of 15 years was 13.8 per 100,000. The incidence of childhood cancer in Australia is rising. Significant increases were seen in acute non-lymphoblastic leukaemia, astrocytoma and melanoma. The age-standardised incidence of 14.4 per 100,000 is about 34% higher than in the UK. Most types of cancer had a higher incidence in Australia than in the UK, and the difference was significant for acute lymphoblastic leukaemia, astrocytoma and melanoma. Of particular interest is malignant melanoma, whose incidence in Australia is more than 5 times that in the UK, as a result of excessive UV exposure. Australia has a higher incidence of Ewing's tumour than osteosarcoma, nearly twice that of the UK. International comparative studies may help to elucidate the aetiology of these tumours.

Acute lymphoblastic leukemia. A comprehensive review with emphasis on biology and therapy

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. It is now curable in 60-70% of children. Most of the current understanding of the biology and treatment of ALL originates from studies of children. In adults, although much progress has been achieved, ALL is curable in only 20-35% of patients.

METHODS

A review of the biology and treatment of ALL from the English literature was performed.

RESULTS

Immunophenotypic and cytogenetic analyses of ALL have contributed to a more rational classification of ALL. These analyses have identified subgroups with poor prognosis or with different therapeutic requirements. Overall, 60-70% of adults with ALL have poor prognostic features, including older age, a high leukocyte count, non-T-cell immunophenotype, Ph-positive genotype, and longer time to achieve a complete remission. These patients have a cure rate of 20-25%, whereas those without these risk factors, have a 60-70% probability of survival. The use of more intensive induction regimens with growth factor support may improve survival rates. Also, intensive consolidation-intensification may improve survival rates. Most patients benefit from maintenance therapy, but the dose schedule must be optimized. Central nervous system (CNS) prophylaxis is beneficial, particularly for patients with a high risk for CNS relapse and when introduced early during induction of remission. Patients with high risk characteristics may benefit from allogeneic bone marrow transplantation (BMT) during first remission, and all other patients may benefit from it during first or subsequent relapse. Autologous BMT may be a valuable option for poor compliant patients.

CONCLUSIONS

Although the prognosis of patients with ALL has improved markedly during the past decades, newer strategies, including more dose-intensive therapy, the search for new drugs, and more target-specific therapy, are needed to improve the current cure rates.

Immunophenotyping of acute lymphoblastic leukaemia in Madras, India

At the Cancer Institute, Madras, India, we have performed immunophenotyping in 125 untreated cases of acute lymphoblastic leukaemia using a panel of 16 monoclonal antibodies and the avidin-biotin immunoperoxidase technique in a haematology autoanalyser (Technicon Hi system). Our results demonstrate a marked difference in the phenotypic pattern of ALL compared to Western countries, the predominant finding being a relative excess of T-ALL and a paucity of C-ALL cases. Age distribution of C-ALL reveals a peak at 2-6 years in paediatric ALL cases.

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.

Adult and childhood acute lymphocytic leukemia: are they different diseases?

Age has long been recognized as an important factor in predicting response to treatment for acute lymphocytic leukemia (ALL). Specifically, the results of treatment of childhood ALL have been far superior to the treatment of what appears to be the same disease in adults. However, from an analysis of the clinical and biological prognostic factors known to be predictive in childhood ALL, there is a striking difference in their distribution in adults with ALL. It appears that there is a special form of ALL seen in children of some populations with a peak incidence of three to seven years. This treatment responsive leukemia appears to be different clinically, biologically, and epidemiologically from adult ALL.

Neonatal exposure to protoporphyrin-activating lighting as a contributing cause of childhood acute lymphocytic leukemia

While being a relatively rare disease, acute lymphocytic leukemia (ALL) is the leading form of cancer in children in the developed world today. ALL sharply peaks in incidence at ages three to four years. In the United States there have been persistent, unexplained increases in incidence of ALL in the past two decades. We hypothesize that exposure to photosensitizing lighting immediately after birth may be a contributing cause of ALL. Fluorescent lamps and other light sources with strong illumination, around 400 nanometers, are protoporphyrin-activating. Activation of protoporphyrin produces superoxides and free radicals that can induce breaks in DNA. In newborn nurseries in the US, the intensity of lighting has increased five- to 10-fold over the past two decades. Thus, protoporphyrin-activating light may be a contributing cause of childhood ALL. Additional retrospective and prospective studies should be undertaken of the relationship between exposure of newborns to protoporphyrin-activating illumination and the development of childhood ALL, along with in vitro studies of the hematologic effects of fluorescent lighting. Protoporphyrin-activating lighting is clearly not the sole determinant of ALL, but it could be a completely preventable cause. Inexpensive plastic filters could reduce these exposures substantially.

Correlation between car ownership and leukaemia: is non-occupational exposure to benzene from petrol and motor vehicle exhaust a causative factor in leukaemia and lymphoma?

Although there is widespread agreement that many cancers have environmental causes we are often unable to see associations between specific cancers and exposure to environmental chemicals. One might also speculate that the more widespread, common-place and 'normal' a chemical exposure is perceived to be then the less likely it will be that the exposure is recognised, let alone be considered to cause cancer. Widespread contamination of air by chemicals associated with internal combustion may be an example of one such 'invisible' carcinogenic exposure. Yet evidence is available which suggests that many leukaemia and lymphoma cases, as well as other cancers, may be caused by this mundane and ubiquitous environmental contamination. The hypothesis is developed that leukaemia 'clustering' as well as national leukaemia incidence may be related to non-occupational exposure to benzene formed by petrol combustion and resulting from petrol evaporation. The possible association between exposure to fuel vapours, internal combustion products and cancer merits much closer examination than it receives at present.

An analysis of associations between social class and ambient magnetic fields in metropolitan Melbourne

In the course of a study on residential magnetic-field exposure, some incidental data were obtained that bear on the issue of confounding of magnetic field exposure by social class. We have explored the possibility that the magnetic flux density of 50 Hz fields measured in Melbourne streets is correlated with a number of variables that index the socio-economic status of the neighborhood. We have examined also for a correlation between field-intensity levels and sums of some or all of the indicators, which were weighted to provide an overall score on socio-economic status. Although some of the indexes were weakly, but significantly, correlated with environmental levels of magnetic fields, the combined indices were not. These results indicate that socio-economic status is not likely to be a confounder in epidemiological studies of residential exposure to ELF magnetic fields in Melbourne.

Impaired pubertal growth in acute lymphoblastic leukaemia

The growth of 182 patients who were long term survivors of childhood acute lymphoblastic leukaemia was retrospectively analysed. All remained in first remission and were treated with either 1800 or 2400 cGy of cranial irradiation. None had been treated with either testicular or spinal irradiation. Ninety three (51 boys, 42 girls) were treated with 2400 cGy and 89 (42 boys, 47 girls) were treated with 1800 cGy cranial irradiation. All patients were treated with standard chemotherapy including intrathecal methotrexate in similar dose regimens in either group. Mean age (SD) at diagnosis in the group treated with 2400 cGy was 4.8 (2.6) years and mean age in the group treated with 1800 cGy was 6.5 (3.3) years. Mean height SD score at diagnosis in the 2400 cGy group was +0.29 and final height achieved was -0.63. Mean height SD score at the start of treatment in the group treated with 1800 cGy was +0.40 and mean final height was -0.53. There was a similar reduction in height SD score in both groups during the pubertal growth spurt. The decrement in height SD score was greater when treatment was administered at less than 7 years of age in either dose regimen, both in prepubertal and pubertal growth. However, the decrease in height SD score was found to be greater in girls than boys. There was a trend in both sexes for the onset of puberty to be at a younger age with a lower treatment dose of radiotherapy. However, in girls treated with the lower dose regimen there was a significant reduction in the mean age of onset of puberty which was 9.9 years. Our data suggest that girls treated at less than 7 years of age have a severe impairment of pubertal growth, which is probably a combination of the dual endocrinopathy of premature puberty and growth hormone insufficiency.

The age incidence of childhood acute lymphoblastic leukaemia

A mathematical model of childhood acute lymphoblastic leukaemia (ALL) is presented which is based on the assumptions that: 1) malignant clones of lymphoblasts arise by spontaneous mutation; 2) this is normally prevented by repair systems which either cause intracellular DNA repair or eliminate the malignant clone; and 3) the repair systems are fallible and their performance decays at random with time. If the major drive to lymphocyte division is microbial antigens then the model produces a reasonable fit to published data on the age distribution of ALL. Furthermore the model offers an explanation for the apparent increase in the incidence of ALL which is associated with improved social conditions.

Case-control study of leukaemia and non-Hodgkin's lymphoma in children in Caithness near the Dounreay nuclear installation

OBJECTIVE

To examine whether the observed excess of childhood leukaemia and non-Hodgkin's lymphoma in the area around the Dounreay nuclear installation is associated with established risk factors, or with factors related to the plant, or with parental occupation in the nuclear industry.

DESIGN

Case-control study.

SETTING

Caithness local government district.

SUBJECTS

14 cases of leukaemia and non-Hodgkin's lymphoma occurring in children aged under 15 years diagnosed in the area between 1970 and 1986 and 55 controls matched for sex, date of birth, and area of residence within Caithness at time of birth.

MAIN OUTCOME MEASURES

Antenatal abdominal x ray examination; drugs taken and viral infections during pregnancy; father's occupation; father's employment at Dounreay and radiation dose; distance of usual residence from the path of microwave beams, preconceptional exposure to non-ionising radiation in the father; and other lifestyle factors.

RESULTS

No raised relative risks were found for prenatal exposure to x rays, social class of parents, employment at Dounreay before conception or diagnosis, father's dose of ionising radiation before conception, or child's residence within 50 m of the path of microwave transmission beams. Results also proved negative for all lifestyle factors except an apparent association with use of beaches within 25 km of Dounreay. However, this result was based on small numbers, arose in the context of multiple hypothesis testing, and is certainly vulnerable to possible systematic bias.

CONCLUSION

The raised incidence of childhood leukaemia and non-Hodgkin's lymphoma around Dounreay cannot be explained by paternal occupation at Dounreay or by paternal exposure to external ionising radiation before conception. The observation of an apparent association between the use of beaches around Dounreay and the development of childhood leukaemia and non-Hodgkin's lymphoma might be an artefact of multiple testing and influenced by recall bias.

Acute lymphoblastic leukaemia among Spanish children and mothers' occupation: a case-control study

STUDY OBJECTIVE

The aim was to investigate the association between mothers' occupational exposure during pregnancy and the incidence of acute lymphoblastic leukaemia in children.

DESIGN

The study was a case-control investigation. A face to face interview was used to assess exposures at work and relevant confounding variables.

SETTING

The study was community based and was carried out in five provinces of Spain.

SUBJECTS

128 cases less than 15 years of age were interviewed (91% of those eligible). Controls (one for each case) were chosen from the census lists and were matched on year of birth, sex and municipality.

MEASUREMENTS AND MAIN RESULTS

Children of mothers working at home had a relative risk (RR) of 7.0 (95% CI = 1.59-30.79) of developing acute lymphoblastic leukaemia. Exposure to organic dust was associated with a RR of 5.5 (95% CI = 1.21-24.8). There was a statistically significant interaction between exposure to organic dust and working at home. The majority of women working at home were hired by local industries to sew different types of tissues (cotton, wool, synthetic fibres) on a machine.

CONCLUSION

A similar association has not been reported before: if confirmed, this finding may suggest a new health concern.

Season-of-birth and acute leukemia of infancy

Because of its short and clearly delineated latency period, acute leukemia of infancy is particularly suited to etiologic analysis. From 1950 to mid-1985, 31 infants with acute leukemia (less than 1 year of age) were registered at the University of Texas, M.D. Anderson Cancer Center at Houston. The medical records of these infants were reviewed for demographic and birth information. Of the 31 infants, 14 (45%) were Hispanic. The sex ratio was 3:1 male/female) for white infants and 5:9 for Hispanic infants. Of the white infants, half had acute lymphocytic leukemia, compared with all but one of the Hispanic infants. There was a significant excess of winter births among the infants diagnosed with acute leukemia (P less than 0.05). The significant association between season-of-birth and the occurrence of leukemia cases is suggestive of periodicity of an environmental etiologic agent, perhaps acting in concert with endogenous rhythmicities in susceptibility to that agent. This finding is deserving of further study.

Epidemiology of the childhood acute leukemias

Epidemiologic studies of the childhood leukemias have provided information relevant to several aspects of the care and follow-up of these children. The observations made regarding in utero radiation and ALL risk have certainly curtailed the use of routine obstetric diagnostic radiographs; observations regarding the association between birth weight, fetal loss, and other gestational events provide added enthusiasm for further research into basic biologic events occurring during fetal development; and the genetic patterns of disease supply critical information for genetic counseling and follow-up of affected patients and families. Additionally, the continued epidemiologic surveillance of children with cancer serves to form the foundation from which we will assess any future changes in childhood cancer incidence or pattern. Although not discussed here, the epidemiology of late effects, including second malignancies, reproductive function, and neuropsychologic functioning will assume a more prominent role as more children survive ALL and move into adulthood. While analytic studies have yet to yield an association as strong as the lung cancer/cigarette association in adults, future research designed to isolate biologically homogeneous disease populations for study may lead us to new and important associations. The continued cooperation of large pediatric oncology groups and private physicians is crucial as these future investigations are undertaken.

Racial differences in acute lymphocytic leukemia mortality and incidence trends

Mortality and morbidity rates for childhood leukemia are examined with reference to time trends and racial differences. Prior to 1964, white and nonwhite children had very different acute lymphocytic leukemia (ALL) mortality rates. With the advent of successful chemotherapy, the mortality rate of ALL in white children has decreased resulting in virtually no racial differences in ALL mortality. The reasons for a stable ALL mortality rate in nonwhite children despite successful chemotherapy include poor access to health care, undefined socioeconomic factors and a biologically different type of ALL occurring in nonwhite children. Recent data from two cancer surveys (1969-1971, 1973-1976) reveal that nonwhite children have a lower incidence of ALL than white children. Underreporting in the nonwhite children could partly account for the difference, but other contributing factors might include a genetic predisposition, undefined socioeconomic influences, and perhaps, a viral agent. Further studies of the factors contributing to racial differences in ALL incidence and mortality are needed.

Review of cancer among 4 religious sects: evidence that life-styles are distinctive sets of risk factors

The occurrence of various types of cancer have been reviewed and evaluated in 4 religious groups. These patterns have been critically assessed in light of the distinctive life-style features of these groups. All 4 religious groups considered in this paper have reduced overall rates of cancer, suggesting that the life-styles of all 4 groups have merit in terms of reducing the overall risk of cancer. The rate of smoking among these groups is nearly nil, and the lung cancer rate in all 4 of these religious groups is strikingly low. Cancer of the oral structures, pharynx, larynx, and esophagus is also generally quite low. Amish and Hutterites have unusually high rates of breast cancer and juvenile leukemia. Reproductive factors frequently mentioned as risk factors for breast cancer cannot explain the excess breast cancer in the Amish and Hutterite women because they should have had the effect of reducing the rate. None of the numerous risk factors, normally suggested for leukemia, are consistent with this observation. The observations on ovarian cancer tend to confirm low parity and late age at first birth as risk factors, although the evidence is not entirely consistent. Also, contrary to common observations, the pattern of ovarian cancer contrasts greatly with the breast cancer pattern, suggesting dissimilar risk factors. Their low rate of cervical cancer is consistent with promiscuity being a strong risk factor, but other frequently suggested risk factors were generally inconsistent with the observations. Cancers of the stomach, colon, rectum, urinary bladder and prostate, in these 4 religious groups, are not readily explained by the risk factors commonly implicated in cancer of these sites. The patterns of a few types of cancers were consistent with the prevailing opinions of risk factors, but some cancers were poorly explained and, in some cases, the cancer patterns contradicted commonly held opinions concerning risk factors. Religions that provide strong directives for the personal lives of adherents result in distinctive life-style, reflecting multiple disease related factors (risk factors and protective factors). Disease related factors are related to each other in simple or more complex ways (e.g. additive, multiplicative or even more complex). Therefore, when dealing with distinctive life-styles, it may be unwarranted to attempt to isolate individual risk factors.

The health of children of low-income families

Childhood poverty is common in Canada: 1,114,000 children under 16 years of age live below the poverty line. The incidence is highest among children of single mothers, unemployed parents, Canadian native peoples and recent immigrants, particularly refugees. Compared with the national average, the infant mortality rate is twice as high, deaths from infectious diseases are 2.5 times more common and accidental deaths are twice as common among children of low-income families. Other problems associated with poverty are iron deficiency anemia, dental caries, chronic ear infections, mental retardation, learning disabilities, poor school performance and increased suicide rates. Health care professionals can help address the poor physical and mental health associated with poverty in children by promoting a broad range of public policies.

Childhood leukaemia in the West Berkshire and Basingstoke and North Hampshire District Health Authorities in relation to nuclear establishments in the vicinity

During the years 1972-85, 89 children aged 0-14 were registered with leukaemia in the West Berkshire and Basingstoke and North Hampshire District Health Authorities. Two nuclear establishments are located within the health authorities, and a third is situated nearby. Fifty of the 143 electoral wards in the two district health authorities lie wholly within, or have at least half their area lying within, a circle of radius 10 km around the establishments. In those 50 electoral wards 41 children aged 0-14 were registered with leukaemia, 28.6 registrations being expected on the basis of leukaemia registration rates in England and Wales (incidence ratio = 1.4, p less than 0.05). This excess was confined to children aged 0-4, among whom there were 29 registrations of leukaemia, 14.4 being expected (incidence ratio = 2.0, p less than 0.001). In the remaining 93 electoral wards there was a small and non-significant increase in the number of registrations of leukaemia at age 0-14 (48 observed, 40.8 expected; incidence ratio = 1.2). There was no obvious trend in the incidence of childhood leukaemia over the 14 years and the overall occurrence of the malignancy in the 143 electoral wards was consistent with a random distribution. In the surrounding Oxford and Wessex Regional Health Authorities the number of registrations of leukaemia at age 0-14 was virtually identical with that expected on the basis of registration rates in England and Wales (362 observed, 372.5 expected; incidence ratio = 1.0). These data indicate that in the two district health authorities studied there was an excess incidence of childhood leukaemia during 1972-85 in the vicinity of the nuclear establishments. In the West Berkshire and Basingstoke and North Hampshire District Health Authorities an average of 60,000 children aged 0-14 lived within a 10 km radius of a nuclear establishment each year. The normal expectation of leukaemia in these children was two cases a year, whereas the recorded incidence was three cases per year, representing one extra case of leukaemia each year among these 60,000 children.

The inter-regional epidemiological study of childhood cancer (IRESCC): a case control study of aetiological factors in leukaemia and lymphoma

The inter-regional epidemiological study of childhood cancer analysed data on 234 children diagnosed with leukaemia or lymphoma and 468 controls matched for age and sex. A wide range of potential risk factors was examined, including prenatal exposure to x rays, maternal drug ingestion and smoking, child's medical history, and parental medical conditions and occupation. Calculations were completed for leukaemia or lymphoma and diagnostic subgroups, as defined by laboratory confirmed cell type. In utero exposure to narcotic analgesics was weakly associated with leukaemia or lymphoma but no other antenatal factors gave significant risks. New associations were identified for skin diseases in both parents and congenital abnormalities in the mothers of children with leukaemia. For past medical conditions in the child, viral disease occurring under 6 months of age increased the risk for acute lymphoblastic leukaemia. Fewer children in the leukaemia or lymphoma group had been immunised compared with the control groups. Case children diagnosed over the age of 9 years were more likely than controls to have had four or more previous episodes of illness. Overall, these results indicate that prenatal factors may be less important than postnatal or genetic influences in the development of leukaemia or lymphoma in children.

What causes childhood leukaemia? Some beliefs of parents of affected children

The theories of parents about the cause of their children's leukaemia have been documented in the course of a case-control study. From a sample of 175 children who were diagnosed as having acute lymphoblastic leukaemia, 91.4% of their parents put forward their theories. Some of these theories were related clearly to material that had been published and therefore had some scientific validity. Other theories often had no apparent scientific basis. Persons who are involved in the care of children with leukaemia should be aware of the wide variety of theories that are held by their parents so that they may provide counselling which could be of help in the relief of feelings of anxiety or guilt among the parents. Parents should always be afforded the opportunity to put forward their own theories so that they may be discussed on a rational basis. It is conceivable that some parents might put forward new hypotheses about leukaemogenesis that could be tested scientifically.

Parental occupations and cancer: a review of the literature

Parental occupation is a suspected risk factor in the occurrence of childhood cancer. Fourteen epidemiological studies investigating a possible association are reviewed and observations are found to be contradictory. Several reports show significant associations for occupations involving exposure to hydrocarbons, lead or chemicals and occupations of social classes I and II. Conversely, some studies find no association at all. Methodological variations do not account for the contrasting results so further investigation is required.