Cohort mortality study of workers at seven beryllium processing plants: update and associations with cumulative and maximum exposure.

OBJECTIVES: To extend follow-up of cause-specific mortality in workers at seven beryllium processing plants and to estimate associations between mortality risk and beryllium exposure. METHODS: 9199 workers were followed for mortality from 1940 through 2005. Standardised mortality ratios (SMRs) were estimated based on US population comparisons for lung, nervous system and urinary tract cancers, chronic obstructive pulmonary disease (COPD), chronic kidney disease, and categories containing chronic beryllium disease (CBD) and cor pulmonale. Associations with maximum and cumulative exposure were calculated for a subset of the workers. RESULTS: Overall mortality in the cohort compared with the US population was elevated for lung cancer (SMR 1.17; 95% CI 1.08 to 1.28), COPD (SMR 1.23; 95% CI 1.13 to 1.32), and the categories containing CBD (SMR 7.80; 95% CI 6.26 to 9.60) and cor pulmonale (SMR 1.17; 95% CI 1.08 to 1.26). Mortality rates for most diseases of interest increased with time-since-hire. For the category including CBD, rates were substantially elevated compared to the US population across all exposure groups. Workers whose maximum beryllium exposure was ≥ 10 µg/m(3) had higher rates of lung cancer, urinary tract cancer, COPD and the category containing cor pulmonale than workers with lower exposure. Significant positive trends with cumulative exposure were observed for nervous system cancers (p = 0.0006) and, when short-term workers were excluded, lung cancer (p = 0.01), urinary tract cancer (p = 0.003) and COPD (p < 0.0001). CONCLUSION: These findings reaffirm that lung cancer and CBD, and suggest that COPD and nervous system and urinary tract cancers, are related to beryllium exposure. Cigarette smoking and exposure to other lung carcinogens are unlikely to explain these elevations.

Reduction of N-nitroso-N-ethylurea-induced neurogenic tumors by X-radiation: a life-span study in rats.

Whole-body X-irradiation after neonatal injection with N-nitroso-N-ethylurea (ENU) significantly reduced the incidence of induced neurogenic tumors in inbred HMT rats kept for their complete life-span. After administration of 10 mg ENU/kg and 1.25 Gy X-radiation, the incidence of schwannomas but not of gliomas was reduced as compared to the incidence in rats given 10 mg ENU/kg only. In contrast, after administration of 4 mg ENU/kg, 1.25 Gy reduced the incidence of gliomas but not of schwannomas. Administration of 1.25 Gy alone induced a remarkably high incidence of rats with neurogenic tumors (20%). Latency of tumor detection was not significantly affected by radiation. Among the most frequently occurring nonneurogenic tumors, squamous cell carcinomas were reduced in incidence by treatment with ENU, 1.25 Gy X-radiation, or both combined. No treatment affected the incidence of pituitary or mammary tumors. There was a preponderance of ovarian tumors in rats given 4 mg ENU/kg + 1.25 Gy. An incidental finding was the occurrence of granular cell tumors in 7 rats from different treatment groups.

Association of chromosome 4 abnormalities with ethylnitrosourea-induced neuro-oncogenesis in the rat.

Cytogenetic studies of rat neurogenic tumor lines induced by ethylnitrosourea (ENU) have shown specific involvement of chromosome 4. The study reported here further characterizes the association of chromosome 4 abnormalities in rat tumor cell lines with regard to etiological agent, tissue of origin, and tumorigenic potential of cloned lines. Lines from rat gliomas induced by avian sarcoma virus did not show abnormalities of chromosome 4. ENU-induced rat tumors of nonneurogenic origin had numerical and/or structural abnormalities of chromosome 4 in seven of nine cell lines. In a comparison of two tumorigenic and two nontumorigenic cloned cell types from the same ENU-induced rat neural tumor, all showed excess chromosome 4. In addition, preneoplastic nervous system tissue, exposed to ENU in vivo, was cultured and sequentially monitored for the concurrent development of chromosome abnormalities and neoplastic properties. Abnormalities of chromosome 4 were observed in 3 of 14 tumorigenic lines and one nontumorigenic clone. The remaining lines had normal karyotypes or abnormalities involving chromosomes other than chromosome 4. Our results suggest that chromosome 4 abnormalities appear late in tumor development, are probably secondary to the tumorigenic potential of the studied cell lines, and apparently are not tissue specific. However, abnormalities of chromosome 4 may be associated preferentially with ENU oncogenesis.

Dose-related reduction by prenatal x-irradiation of the transplacental neurocarcinogenicity of ethylnitrosourea in rats.

Pregnant Sprague-Dawley rats were X-irradiated on the 16th day of gestation with 5 to 250 rads and given i.p. injections 4 days later with 10 mg ethylnitrosourea per kg. The offspring were observed over their life span for the appearance of neurogenic tumors. The frequency of animals surviving beyond 4 weeks of age that developed tumors was inversely related to X-ray dose. About 15% developed tumors after exposure to the largest doses, 39 to 46% after the intermediate doses, and 58 to 65% after the smallest doses; 69% tumors occurred after treatment with ethylnitrosourea alone. The reductions in tumor frequency were not due to the increased mortality rate of tumor-prone animals, either before or after the onset of tumor appearance. Mean offspring weight at 4 weeks and 4 months of age was inversely related to X-ray dose but was not significantly different in those animals later developing tumors from that in animals remaining tumor free. Mean time of tumor appearance and mean number of tumors per affected animal were unrelated to tumor frequency. It does not seem that the destruction of target cells is by itself sufficient to explain the results.

Short-term tissue culture observations of experimental primary and transplanted nervous system tumors.

Tumors of the central and peripheral nervous system were induced in BD-IX rats and transplanted serially. Both primary and transplanted tumors in different generations were cytologically analyzed, using primary explants in vitro. Four hundred and thirty single tumors were examined in vitro over th period 1969 to 1977, using the following methods: conventional aniline staining, special silver impregnation, supravital observation of cells by phase contrast microscopy, locomotion studies with time-lapse cinematography, and ultrastructural analysis from transmission and scanning electron microscopy. Cells grown in vitro were subdivided into the following groups, according to their morphology: (1) Apolar cells: Round cells only observed in rare tumors of the nasal cavity and sporadically in transplanted neurinomas; they are thought to represent cells from the reticular variant of neurinoma in the latter. (2) Bipolar cells occurred in two forms: As bipolar fibroblasts and as slender bipolar cells observed in explants of malignant neurinomas. The latter cells grow in parallel arrangements; their tentative interpretation as Schwann cells is consistent with their description in human neurilemomas. (3) Semipolar cells with one clear-cut edge and a broad ruffled membrane opposite. They are described as fibroblasts in the course of locomotion. (4) Multipolar cells, observed in several forms in primary and transplanted gliomas exclusively. Variants with long processes were seen in the first passages of intracerebrally transplanted tumors only; in later generations, all cells had short branching processes and little cytoplasm. Conclusions concerning the cytologic derivation of experimental tumors are discussed.

Phenobarbital lacks promoting activity for neurogenic tumors in F344 rats transplacentally exposed to ethylnitrosourea.

A chronic rodent study in F344 rats was conducted to investigate the promoting ability of phenobarbital (PB) on neurogenic tumors initiated by transplacental administration of ethylnitrosourea (ENU). Pregnant F344 rats were given a single intravenous dose of 3.5 mg ENU/kg or vehicle on the twentieth day of gestation. A total of 192 male offspring were divided into four groups: ENU-PB, ENU-control, PB-control, and control-control. Rats in ENU-PB and PB-control groups received 0.05% PB in their drinking water from four to 78 weeks of age. Nervous system tumors were induced only in animals exposed to ENU. The difference in the incidence of neuroectodermal tumors in rats that were ENU initiated only (13/37; 35%) compared to the incidence in rats that were initiated and given PB (13/57; 23%) was not statistically significant (p greater than 0.05). ENU-control and ENU-PB treatment groups exhibited no differences in tumor multiplicity or tumor latency. These results demonstrate that PB lacks promoting activity for neurogenic tumors in F344 male rats transplacentally exposed to ENU.

Effect of irradiation on ethyl nitrosourea induced neural tumours in Wistar rat.

Wistar rats received 2 Gy whole body irradiation followed immediately by 10 mg/kg of ethyl nitrosourea (ENU) on the day of birth. Out of 33 rats which were given ENU alone 14 developed 22 tumours of the nervous system, out of which 15 (68.2%) were gliomas and 7 (31.8%) were Schwannomas. Out of 34 rats which were given both irradiation and ENU 12 were found to harbour 15 neural tumours out of which 14 (93.3%) were gliomas and 1 (7.1%) was a Schwannoma. The pretreatment with irradiation seems to have resulted in selective suppression of Schwannoma induction.

Increased c-Ki-ras expression in hamster lung exposed to N-nitrosodiethylamine and hyperoxia as detected by the polymerase chain reaction.

Neuroendocrine lung cancers can be induced in hamsters within 8-12 weeks by combined exposure to N-nitrosodiethylamine (DEN) and hyperoxia. The expression of the c-Ki-ras gene in this lung cancer model was studied using polymerase chain reaction analysis of mRNA (RNA/PCR). We used four different groups of hamsters, exposed for 6 weeks to DEN with hyperoxia (60% oxygen), DEN, hyperoxia, or ambient air, respectively. Total RNA was isolated from lung tissues and cDNA made prior to PCR amplification. A 234-bp product was amplified from c-Ki-ras cDNA and quantitated using scanning laser densitometry. The data obtained were normalized to the expression of the house keeping gene B-actin. The c-Ki-ras products were present after amplification of all hamster lung RNA samples. The hamster lungs exposed to DEN with hyperoxia displayed higher c-Ki-ras protooncogene expression than hamsters exposed to DEN, hyperoxia, or ambient air alone. Since the animals studied were sacrificed at 6 weeks, prior to the appearance of tumors, we conclude that this increased expression may indicate a role for c-Ki-ras in the initial steps in malignant transformation of neuroendocrine cells.

Study of postnatal effects of chemopreventive agents on offspring of ethylnitrosourea-induced transplacental carcinogenesis in rats. I. Influence of retinol acetate, alpha-tocopherol acetate, thiamine chloride, sodium selenite, and alpha-difluoromethylornithine.

We studied the influence of the vitamins retinol acetate, alpha-tocopherol acetate and thiamine chloride; the antioxidant sodium selenite and an inhibitor of polyamine biosynthesis, alpha-difluoromethylornithine, on the offspring of transplacental carcinogenesis by ethylnitrosourea in rats. Ethylnitrosourea was given to pregnant rats as a single i.v. injection, at a dose of 75 mg/kg body wt. or 5.5 mg/kg body wt., on the 21st day after conception. Retinol, tocopherol or thiamine was added to the diet, and selenite and alpha-difluoromethylornithine to drinking water of the offspring throughout their postnatal life at moderate doses. In control groups, ethylnitrosourea induced tumors of brain, spinal cord, peripheral nervous system and kidneys in the offspring. alpha-Difluoromethylornithine exerted a slight inhibitory effect; this agent decreased the total tumor multiplicity and the multiplicity of peripheral nervous system tumors and also prolonged survival time. Retinol, tocopherol, thiamine and selenite did not influence the development of the transplacentally-induced tumors.

Paternal occupational exposures and childhood cancer.

The objective of the study described here was to test the hypothesis that paternal occupational exposure near conception increases the risk of cancer in the offspring. We conducted a cohort study based on a population of 235,635 children born shortly after two different censuses in Sweden. The children were followed from birth to 14 years, and cases of cancer were identified in the Swedish Cancer Registry. Occupational hygienists assessed the probability of exposure to different agents in each combination of the father's industry and occupation as reported in the censuses. We also analyzed individual job titles. We compared the cancer incidence among children of exposed fathers to that among children of unexposed fathers using Cox proportional hazards modeling. The main findings were an increased risk of nervous system tumors related to paternal occupational exposure to pesticides [relative risk (RR) = 2.36; 95% confidence interval (CI), 1.27-4.39] and work as a painter (RR = 3.65; 95% CI, 1.71-7.80), and an increased risk of leukemia related to wood work by fathers (RR = 2.18; 95% CI, 1.26-3.78). We found no associations between childhood leukemia and paternal exposure to pesticides or paint. Our results support previous findings of an increased risk of childhood brain tumors and leukemia associated with certain paternal occupational exposures. Some findings in previous studies were not confirmed in this study.

Age- and dose-dependent transplacental carcinogenesis by N-nitrosoethylurea in Syrian golden hamsters.

Syrian golden hamsters have a very short period (15 days) of gestation. The implantation of the blastocyst occurs on day 5, embryogenesis proceeds very rapidly thereafter and neural tube closure is completed by day 9. In the present study the effects of two different doses of N-nitrosoethylurea (NEU) administered at various stages of gestation were quantitatively evaluated in Syrian golden hamsters. NEU at either 0.2 or 0.5 mmol/kg was administered transplacentally as a single i.p. injection to pregnant hamsters on gestation days 7, 8, 9, 10, 11, 12, 13, or 14. The incidence, latency period and multiplicity of tumors varied with the dose of NEU and the stage of development at the time of NEU administration. Although tumors of the peripheral nervous system predominated, a variety of other tumors, including melanomas and visceral tumors of epithelial and mesenchymal origin, were also observed in hamster offspring exposed transplacentally to NEU. Sensitivity to transplacental carcinogenesis was maximal during late gestation and very low before day 9.

Experimental chemotherapy with N'N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) in autochthonous neurogenic tumors of the rat transplacentally induced by ethylnitrosourea.

Autochthonous neurogenic tumors of the rat induced by transplacental application of ethylnitrosourea were used for the first time to study their suitability as tumor models for experimental chemotherapy. Of 189 transplacentally treated rats, 87% developed neurogenic tumors. After the initial clinical diagnosis of a neurogenic tumor, additional malignant tumors often occurred. The mean number of neurogenic tumors from 62 untreated control rats increased from 1.0 per rat at the time of randomization to 1.2 as revealed by autopsy and 1.5 tumors by histological examinations. Out of all neurogenic tumors, tumors of the brain were observed in 31%, tumors of cranial nerves in 36% (90% tumors of trigeminal nerve), tumors of spinal cord in 21%, and tumors of peripheral nerves in 10%. The median survival time until natural death of 62 control rats was 228 days. Rats with tumors of peripheral nerves lived shortest, followed by rats with tumors of cranial nerves, tumors of the spinal cord, and brain tumors. Brain tumors were mainly astrocytomas and oligodendrogliomas. The survival time of untreated rats from randomization to natural death was longest for those with brain tumors, followed by tumors of peripheral nerves, cranial nerves, and tumors of the spinal cord. There was great variation in survival time from a few days to more than 6 months. To study the responsiveness to chemotherapy, 62 rats received BCNU as a single intravenous dose of 9 and later 10 mg/kg. Sixty-two untreated control rats had a median survival time of 36 days (95% confidence interval 26-52 days), the treated rats 43.5 days (26-62 days). The difference was not statistically significant. BCNU produced a remission or a no change of neurologic symptoms in 60% (37 out of 62) in comparison to 39% (24 out of 62) in the control group (p less than 0.05). The advantages and disadvantages of the present models are discussed. Due to methodical problems and the marginal response to BCNU, autochthonous neurogenic tumors of the rat are not suitable as models for chemotherapeutic studies.

The effect of nerve growth factor and antibodies to nerve growth factor on ethylnitrosourea carcinogenesis in mice.

The specific induction of neural tumors by the carcinogen, ethylnitrosourea (ENU), can be enhanced by reducing the in vivo nerve growth factor (NGF) levels in mice using IgG directed against the biologically active subunit of NGF (anti-NGF). This effect is reversible, confirming that the altered endogenous NGF levels do return to normal following injection with anti-NGF. Correspondingly, no neural tumors were observed when in vivo NGF levels were elevated by administering exogenous NGF with ENU. The higher physiological levels of NGF in control mice when compared to control rats might explain why fetal administration of ENU to rats results in a greater percentage of neural tumors. This would suggest that the long studied maturation effect that NGF has on developing neural cels of the peripheral nervous system may also influence neural oncogenesis.

Neural, pituitary, and mammary tumors in Sprague-Dawley rats treated with X irradiation to the head and N-Ethyl-N-nitrosourea (ENU) during the early postnatal period: a statistical study of tumor incidence and survival.

To study the late effects of early postnatal treatment with N-ethyl-N-nitrosourea (ENU) preceded by X irradiation to the head, 226 neonatal CD rats were divided into six groups which received the following treatment: (1) 500-rad X irradiation to the head on the third postnatal day (pnd); (2) injection ip with 30 mg/kg ENU on the fourth pnd; (3) injection ip with 30 mg/kg ENU on the seventh pnd; (4) a combination of 500-rad X irradiation to the head on the third pnd, followed by ip 30 mg/kg ENU on the fourth pnd; (5) a combination of 500-rad X irradiation to the head on the third pnd, followed by ip 30 mg/kg ENU on the seventh pnd; and (6) untreated controls. The results indicate that (1) X irradiation to the head alone significantly extended the life span of females compared to that of control females, and did not affect survival of males; (2) X irradiation did not influence the latent period or mortality from neurogenic tumors when ENU was given 1 or 3 days afterward; (3) ENU itself was a factor in shortening latent periods for mammary tumors; (4) X irradiation alone did not increase the incidence of mammary tumors, and revealed no protective effect on the ENU-induced mammary carcinogenesis; (5) X irradiation increased the prevalence of pituitary tumors in the females; (6) no enhancement of pituitary tumors by ENU was observed: and (7) there was a statistically significant association of pituitary and mammary tumors in females.

Brain and central nervous system cancer mortality in U. S. rubber workers.

Since 1963 the observed mortality experience of BCNS cancers among rubber workers appears to be very comparable to that expected. A possible exception to this statement is the experience of one plant in Akron, Ohio, reported by Monson and Nakano. Excesses in earlier years may also be localized to one or two companies. The results of a case-control study did not support a hypothesized association of elevated BCNS cancer risk with exposures in the tire building/tire assembly segments of the rubber tire manufacturing process. The direction of future epidemiologic studies would benefit by the assembly of as large a number of cases as possible and should focus on calendar periods of exposure, make allowance for a latent period, and include retrospective industrial hygiene assessments of the specific exposures.

Nerve growth factor modification of the ethylnitrosourea model for multiple schwannomas.

The administration of ethylnitrosourea (ENU) to pregnant rats late in gestation or to neonatal rats results in the induction of Schwann cell tumors in a high percentage of perinatally exposed animals. Exogenous administration of nerve growth factor (NGF) significantly reduces the number of Schwann cell tumors and other neurogenic tumors developing in ENU-treated rats. Administration of antibodies directed against NGF prior to neonatal ENU exposure results in a substantial increase in the incidence of Schwann cell tumors, particularly in the trigeminal nerves of both rats and mice. Transplacental ENU treatment causes early neoplastic proliferation (ENP) at 90 days of age in the Schwann cell population of trigeminal nerves in nearly all exposed rats. A variety of NGF treatment protocols (single or multiple inoculations or microinfusion prior to or following ENU exposure) resulted in a significant reduction in ENU-induced ENP in trigeminal nerves. These results indicate that NGF may convey protection either directly or indirectly, by an unknown mechanism, to Schwann cells and other supportive neural cells by reducing their sensitivity to ENU-induced neoplastic transformation.

Effect of long-term administration of retinoids on rats exposed transplacentally to ethylnitrosourea.

A neurogenic cancer model, involving transplacental administration of ethylnitrosourea (ENU) to Sprague-Dawley rats, was employed to evaluate the efficacy of retinyl acetate, 13-cis-retinoic acid, and all-trans-retinoic acid in prevention of nervous system tumors in the offspring. Supplementation of the diet with either of these retinoids did not alter the incidence, number, or latency period of the induced neurogenic tumors. Long-term administration of high doses of 13-cis-retinoic acid (240 mg/kg of diet) or all-trans-retinoic acid (65 mg/kg of diet) produced lethal toxicity in this strain of rats, possibly due to interference with vitamin K absorption and the resulting internal hemorrhages associated with hypoprothrombinemia. Prolonged feeding of retinyl acetate increased the retinyl palmitate level in the liver. The concentration reached was not dose-dependent; a maximum level (approximately 10-fold that of controls) was observed after six months of feeding. An unexpected observation was the decrease in liver retinyl palmitate concentration in the livers of rats fed 13-cis-or all-transretinoic acid.

Tumour incidence in the progeny of male rats exposed to ethylnitrosourea before mating.

BDVI male rats were given a single i.p. dose of 80 mg/kg b.w. ethylnitrosourea (ENU), and each rat was then mated at weeks 1, 2, 3, 4 and 5 after treatment with 3 untreated females. A decrease in the fecundity of the treated males was observed, particularly when they were mated 5 weeks after ENU treatment. The average litter size was lower in the treated group, especially for females mated in week 4. No significant differences in pre- or post-weaning mortality were noted between control and treated groups. A slight, non-significant increase in the incidence of brain tumours was observed in the progeny of treated males compared with the controls. The incidence of thyroid tumours was significantly higher in controls but this difference disappeared when adjustment was made for litter effect and intralitter dependence.

Neuroblastoma and fetal exposure to phenytoin in a child without dysmorphic features.

Despite the fact that the teratogenic effects of phenytoin have been suggested in several case reports, the evidence for a possible oncogenic potential of phenytoin has not been widely recognized. Recently, neuroblastoma as well as other neuroectodermal and non-ectodermal tumors has been seen in several children exposed to phenytoin prenatally. Previous cases have been almost uniformly associated with the features of "fetal hydantoin syndrome" and none have been developmentally normal. We report a developmentally-normal boy of 21/2 years with an abdominal neuroblastoma whose mother had been on phenytoin (as well as carbamazepine) throughout gestation. We review the various neoplasms which have been reported in the offspring of mothers receiving phenytoin.

Cancer risk in a cohort of licensed pesticide users.

First admissions to the hospital among 25,945 men living in southern Piedmont and holding a license authorizing them to use pesticides were analyzed in a study of the cancer risk related to exposure to pesticides. Standardized incidence ratios significantly higher than one were encountered for malignant skin cancers and lymphomas. The risk of lymphoma was particularly high in predominantly arable areas. The standardized incidence ratios for tumors of the nervous system and hematopoietic tissue showed an interesting age-related pattern and a higher risk in areas primarily devoted to forest tree plantation, but did not reach significance. Certain hypotheses are advanced to explain these findings.