Parental occupation and intracranial neoplasms of childhood: anecdotal evidence from a unique occupational cancer cluster

Unexplained cancer clusters: common threads

A number of identified cancer clusters have followed exposures to mixtures of chemicals. The causes for these cancers could not be attributed to any of the individual chemicals in the mixtures and up to now have remained unexplained. The author presents case studies showing that these previously unexplained cancer clusters have common characteristics. First, they can be attributed to exposures to mixtures that contain at least one lipophilic and one hydrophilic chemical, with octanol:water partition coefficients, K(ow), indicative of lipophilic or hydrophilic character. Second, the specific combinations of lipophiles and hydrophiles act as individual entities and produce cancers not associated with exposure to any of the individual chemicals contained in the mixtures. The cancers that follow these exposures can be in the form of single or multiple cancers per cluster.

A case-control study of parental occupation, leukemia, and brain tumors in an industrial city in Taiwan

We conducted a case-control study in an industrial city in Taiwan to determine whether parents of newly diagnosed patients who were younger than 30 years old with leukemia or brain tumors or the patients themselves were more likely to have been employed in certain occupations or industries. Job histories were collected for parents (and for subjects if they worked) on 103 newly diagnosed cases of leukemia, 74 newly diagnosed cases of brain tumors, and 417 controls matched for age and sex. All jobs since the age of 16 that the subjects held for more than 6 months, a total of approximately 4,000 jobs, were coded for occupation and industry according the standard four-digit system used in Taiwan. Matched-pair analyses were performed comparing cases and controls among all jobs held by subjects and both parents using four-digit occupation and industry codes. Separate analyses also were performed for parental jobs held during the preconception, perinatal, and postnatal periods. Odds ratios (ORs) were adjusted for subject smoking, parental smoking, and exposure to medical radiation. Certain industry and occupation four-digit codes were significantly associated with increased odds ratios of childhood tumors. Including work during any or all periods, leukemias were more common in children of fathers who had worked (1) as wood treaters (adjusted OR 16.03, 95% confidence interval CI = 1.77-145.5), and (2) as building finishers and related trades workers (adjusted OR 4.08, 95% CI = 1.12-14.8), whereas brain tumors were more common in children of mothers who had worked (1) in electronic parts and components manufacturing (adjusted OR 13.78, 95% CI = 1.47-129.0) and 2) as textile and garment workers (adjusted OR 7.25, 95% CI = 1.42-37.0), as well as in subjects who had worked with certain electronic parts and components (adjusted OR 28.67, 95% CI = 2.88-285.6). Leukemias were more common in children of fathers who had worked in the preconception period (1) as wood treaters (adjusted OR 12.17, 95% CI = 1.36-109.2), (2) as building finishers and related trades workers (adjusted OR 4.08, 95% CI = 1.12-14.8), (3) as electronic equipment assemblers (adjusted OR 4.56, 95% CI = I 1.05-19.9), and (4) as certain other assemblers (adjusted OR 10.24, 95% CI = 1.02-102.6). In addition, leukemias were more common in children of fathers who had worked in the perinatal period (1) as wood treaters (adjusted OR 13.08, 95% CI = 1.36-125.5) and (2) as building finishers and related trades workers (adjusted OR 4.51, 95% CI = 1.04-19.6). Brain tumors were more common in children of mothers who had worked in the preconception period (1) in electronic parts and components manufacturing (adjusted OR 11.81, 95% CI = 1.20-116.3), and (2) as textile and garment workers (adjusted OR 7.25, 95% CI = 1.18-31.0).

Carcinogenicity test in B6C3F1 mice after parental and prenatal exposure to 50 Hz magnetic fields

Some epidemiological studies suggest association of childhood cancer with occupational exposure of the parents to magnetic fields. To test this relationship, 50 each of C57BL/6J female and C3H/HeJ male mice were exposed for 2 and 9 weeks, respectively, to 50 Hz sham (group A), 0.5 (group B), and 5 mT (group C) sinusoidal alternating magnetic fields. They were mated under the exposure for up to 2 weeks, and the exposure was continued until parturition. All the B6C3F1 offspring, without adjusting numbers of animals, were clinically observed without exposure to magnetic field for a nominal 78 weeks from 6-8 weeks of age after weaning and then euthanized for pathological examination according to a routine carcinogenicity test. 540 pups entered the test, and the survival rate was 96.7%. No F1 mouse died of tumoral diseases before a male in A group died of stomach cancer at 43 weeks of age. The first animal death in the exposed groups due to tumor occurred at 71 weeks of age. Eighteen animals died before necropsy at 84-86 weeks of age. No significant difference was detected in the final number of survivors and incidence of tumors between groups A and B, or A and C. Concerning reproduction total implants in group B were less than in group A and the difference was on the borderline of significance (P=.05). This difference was not reproduced in a later duplicate experiment.

Epidemiology of childhood brain tumors

BACKGROUND

Brain tumors comprise more than 20% of all childhood malignancies, and constitute the greatest number of solid pediatric cancers. Incidence rates reported have varied from 2.4 to 3.5/100,000 children, reflecting the impact of modern imaging techniques, the application of diverse investigative methodologies, and the accessibility of the community to health care.

METHODS

Material from patients < 18 years of age was collated from the Manitoba Cancer Foundation Tumor Registry, the personal records of Winnipeg pediatric neurologists, and autopsy data. Patient data were also obtained from hospital charts and operating room log books. Histological sections were examined and classified according to the American Cancer Society by a single neuropathologist. The chi-square test was used for statistical evaluation.

RESULTS

During the seven-year study period, the diagnosis of brain tumor was made in 89 pediatric patients, of which 88 were diagnosed premortem. The overall average annual incidence rate for both sexes was 4.03/100,000 child-years, higher than that previously reported. The male and female average annual incidence rates were 4.2 and 3.7/100,000 child-years, respectively. Tumor type and location were relatively unremarkable, with an expected peak of medulloblastoma occurring in young males. The yearly incidence of tumor occurrence was fairly stable, and the geographic distribution of cases within Manitoba, homogeneous.

CONCLUSION

The highest incidence rates of pediatric brain tumors have been recorded in countries possessing sophisticated universal health care systems, possibly reflecting their efficacy in disease surveillance.

Cancer in offspring of parents engaged in agricultural activities in Norway: incidence and risk factors in the farm environment

In this study of cancer in offspring we demonstrate that factors linked to horticulture and use of pesticides are associated with cancer at an early age, whereas factors in animal husbandry, in particular poultry farming, are associated with cancers in later childhood and young adulthood. Incident cancer was investigated in offspring born in 1952-1991 to parents identified as farm holders in agricultural censuses in Norway in 1969-1989. In the follow-up of 323,292 offspring for 5.7 million person-years, 1,275 incident cancers were identified in the Cancer Registry for 1965-1991. The standardized incidence for all cancers was equal to the total rural population of Norway, but cohort subjects had an excess incidence of nervous-system tumours and testicular cancers in certain regions and strata of time that could imply that specific risk factors were of importance. Classification of exposure indicators was based on information given at the agricultural censuses. Risk factors were found for brain tumours, in particular non-astrocytic neuroepithelial tumours: for all ages, pig farming tripled the risk [rate ratio (RR), 3.11; 95% confidence interval (CI), 1.89-5.13]; indicators of pesticide use had an independent effect of the same magnitude in a dose-response fashion, strongest in children aged 0 to 14 years (RR, 3.37; 95% CI, 1.63-6.94). Horticulture and pesticide indicators were associated with all cancers at ages 0 to 4 years, Wilms' tumour, non-Hodgkin's lymphoma, eye cancer and neuroblastoma. Chicken farming was associated with some common cancers of adolescence, and was strongest for osteosarcoma and mixed cellular type of Hodgkin's disease. The main problem in this large cohort study is the crude exposure indicators available; the resulting misclassification is likely to bias any true association towards unity.

Trichloroethylene--a review of the literature from a health effects perspective

This report reviews the literature on the impact of exposure to trichloroethylene (TCE) on human health. Special emphasis is given to the health effects reported in excess of national norms by participants in the TCE Subregistry of the Volatile Organic Compounds Registry of the National Exposure Registries--persons with documented exposure to TCE through drinking and use of contaminated water. The health effects reported in excess by some or all of the sex and age groups studied were speech and hearing impairments, effects of stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.

Parental occupational exposures and risk of childhood cancer: a review

We reviewed the literature in order to summarize the present knowledge on the association between parental occupational exposures to chemicals and the risk of childhood malignancy. The 32 studies pertaining to this topic were evaluated by considering various study qualities such as sample size, specificity of outcome, confounding, exposure specificity, and control selection. When evaluating the findings from any epidemiologic study, the potential sources of bias have to be considered. The selection of subjects, misclassification of exposure or outcome, and confounding from extraneous factors can contribute to a biased estimate of effect. Studies done to minimize these potential biases will be more valid, and these studies should be given the most weight when parental occupational exposures are evaluated as risk factors for childhood malignancy. We conclude that the preponderance of evidence supports the hypothesis that occupational exposure of parents to chemicals increases the risk of childhood malignancy. The parental occupational exposures implicated in childhood malignancy risk are exposure to chemicals including paints, petroleum products, solvents (especially chlorinated hydrocarbons) and pesticides, and exposure to metals. The available data do not allow the identification of specific etiologic agents within these categories of compounds. Future epidemiologic and toxicologic studies should be designed to pursue these leads.