Association of asbestos and bronchogenic carcinoma in a population with low asbestos exposure

Lung Asbestos Bodies and Pulmonary Cancer in Subjects without Occupational Exposure

Lung asbestos bodies were searched for in 65 subjects with pulmonary cancer and without occupational exposure and in 65 matched controls. No significant association between the presence of asbestos bodies and occurrence of lung cancer was found. Nevertheless, adenocarcinoma was significantly associated with the presence of lung asbestos bodies in men. The latter result suggest that, even in non-professionally exposed subjects, the possibility of relationships between asbestos exposure and lung cancer cannot be excluded.

New insights on the biomineralisation process developing in human lungs around inhaled asbestos fibres

Once penetrated into the lungs of exposed people, asbestos induces an in vivo biomineralisation process that leads to the formation of a ferruginous coating embedding the fibres. The ensemble of the fibre and the coating is referred to as asbestos body and is believed to be responsible for the high toxicological outcome of asbestos. Lung tissue of two individuals subjected to prolonged occupational exposure to crocidolite asbestos was investigated using synchrotron radiation micro-probe tools. The distribution of K and of elements heavier than Fe (Zn, Cu, As, and Ba) in the asbestos bodies was observed for the first time. Elemental quantification, also reported for the first time, confirmed that the coating is highly enriched in Fe (~20% w/w), and x-ray absorption spectroscopy indicated that Fe is in the 3+ oxidation state and that it is present in the form of ferritin or hemosiderin. Comparison of the results obtained studying the asbestos bodies upon removing the biological tissue by chemical digestion and those embedded in histological sections, allowed unambiguously distinguishing the composition of the asbestos bodies, and understanding to what extent the digestion procedure altered their chemical composition. A speculative model is proposed to explain the observed distribution of Fe.

Induction of ferritin synthesis in human lung epithelial cells treated with crocidolite asbestos

Crocidolite asbestos is a known human carcinogen containing 27% iron by weight. It has previously been shown that iron was mobilized intracellularly from crocidolite after treatment of human lung epithelial cells (A549) and that the toxicity of the fibers was directly related to how much mobilized iron was in the < 10,000 MW (low-molecular-weight, LMW) fraction [C. C. Chao, L.G. Lund, K. R. Zinn, and A. E. Aust (1994) Arch. Biochem. Biophys. 314, 384-391]. The data here show that iron mobilization from crocidolite began immediately after treatment of the A549 cells and increased linearly with time. However, the synthesis of ferritin, an iron storage protein, did not begin until after 4 h of treatment, reaching a sustained maximum after 12 h. Mobilized iron was preferentially incorporated into the nonferritin-protein fraction up to 7 h after treatment, when the amount of iron mobilized was low and before significant accumulation of newly synthesized ferritin had occurred. This suggested that these cultured cells needed additional iron for synthesis of iron-requiring proteins and that iron mobilized from crocidolite could be utilized directly for this purpose. Subsequent to this, additional mobilized iron was incorporated into newly synthesized ferritin. Even though iron from crocidolite was incorporated into newly synthesized ferritin or into other proteins, the amount of iron from crocidolite in the LMW fraction remained constant during the 24 h. Thus, it appeared that synthesis of ferritin may not have fully protected the cells from the toxic effects of iron mobilized from crocidolite.

Incidence of lung cancer by histological type among asbestos cement workers in Denmark

OBJECTIVE

A significant twofold increased risk of lung cancer was found among 8000 men employed in the Danish asbestos cement industry between 1928 and 1984. The histological pattern of 104 lung cancer cases was studied with the aim of evaluating a relation between specific morphological types, duration of employment, and time since first employment.

METHODS

Age, sex, and calendar time specific incidence of morphological subtypes of lung cancer (adenocarcinoma, squamous cell carcinoma, anaplastic carcinoma, and unspecified malignant tumour) for all Danish men were computed from 1943 to 1984, from data routinely collected by the Danish Cancer Registry. Person-years of observation were counted from 15 years after the date of first employment until date of diagnosis of cancer, death, emigration, or the end of follow up on 31 December 1984. Expected numbers of cases were computed by applying person-years at risk to the appropriate incidence rates. Observed numbers were distributed accordingly and the relative risk calculated.

RESULTS

The relative risk for adenocarcinoma was 3.31 (observed (O) 24, expected (E) 7.26), for squamous cell carcinoma 1.67 (O, 37, E, 22.12), for anaplastic carcinoma 1.58 (O, 23, E, 14.53), and for unspecified malignant tumour 1.57 (O, 18, E, 11.46). An increased risk by duration of employment and time since first employment was most pronounced for adenocarcinoma.

CONCLUSION

The link between adenocarcinoma and asbestos was confirmed in this, the first study of risk of lung cancer by histological category based on incident cancer cases for a whole population during a 50 year period.

Histological type of lung carcinoma in asbestos cement workers and matched controls

Histological types of lung carcinoma were examined in a case series of workers exposed to asbestos cement dust (n = 29) and matched controls (n = 87). The proportion of adenocarcinomas was 31% among the exposed subjects and 15% among the controls (mid-p = 0.05). Among workers with high exposure the proportion of adenocarcinoma was even higher (45%, 5/11; mid-p = 0.03). The proportion of peripheral tumours tended to be higher among exposed cases than controls (24 v 12%, mid-p = 0.12). Lobe of origin did not differ, however, between exposed cases and controls. Thus the study indicates an association between the degree of exposure to asbestos and adenocarcinoma of the lung, and a peripheral rather than central localisation of the tumours, but with virtually the same distribution of lobe of origin as in the general population.

Asbestos exposure and histologic cell types of lung cancer in surgical and autopsy series

A case-control study was carried out on 41 surgical and 106 autopsy histological tissue samples of lung cancer in men, in order to investigate the relationships between asbestos exposure and cell type of pulmonary carcinoma. Both occupational history (obtained by interviews of surgical patients or of the next-of-kin for deceased subjects) and lung asbestos body content (determined by optical count after hypochlorite digestion and membrane filtration of lung tissues) were considered as asbestos exposure indicators. No significant relationships were found in the surgical series after adjustment for smoking. The autopsy series showed a trend towards an association between lung adenocarcinoma and asbestos exposure indicators and a markedly higher agreement between the 2 kinds of indicators than that observed in the surgical series.

Study of asbestos bodies in Japanese urban patients

To study whether low-level exposure to asbestos contributes to lung cancer risk, the asbestos body (AB) content in lung tissue was measured in 476 patients with lung cancer and 369 patients with other diseases, all from a Japanese industrialized city. Eleven patients with histologically confirmed asbestosis were included. The findings were stratified into four groups. A significant number of patients with lung cancer were seen in the groups with high counts, as compared to controls. There was no significant difference in histologic type and site of lung cancer among four groups. The patients with lung cancer in high count groups were significantly younger than those with lower counts. A significant number of smokers were seen in the groups with high AB counts among patients with lung cancer as compared to controls, even if the patients with asbestosis were excluded. These findings suggest that there may be a positive interaction of smoking and exposure to asbestos relative to the incidence of lung cancer even at a low exposure level.

The relationship between lung cancer and asbestos exposure

This study supports the theory that asbestos exposure may be implicated in a recent upsurge of terminal lung cancer cases in Kure, Japan. The number of asbestos bodies found in the lung during autopsy of 158 subjects from 1984 to 1986 suggests that 70.4 percent of the 51 diagnosed lung cancer cases could be attributed to asbestos exposure. Of the 107 subjects in whom death was not caused by cancer, 38.4 percent had significant asbestos exposure. Types of asbestos bodies found in diagnosed lung cancer cases were analyzed using scanning electron microscopy and x-ray analyzer. Chrysotile was the most widely found component, but amphiboles such as crocidolite and amosite also were detected. Residents of Kure had high exposure to the inhalation of asbestos bodies, possibly related to the upsurge in lung cancer deaths. In our earlier report, asbestos exposure was implicated in the increased incidence of malignant mesothelioma in Kure, an active Japanese ship-building port since the 1920s. Our current findings indicate that asbestos exposure may be a pathogenic factor in lung cancer in world seaports where asbestos exposure has been prevalent.

Respiratory morbidity in workers exposed to asbestos in the primary manufacture of building materials

Former employees (214) of a plant that manufactured asbestos-containing building materials (wallboard and acoustic tile) from 1958 through 1974 were screened for asbestos-related pulmonary disease. Results are presented on 182 union members whose names appeared on a 1966 seniority list in one of six departments believed to have had substantial asbestos exposure. The study population demonstrated a high frequency of pulmonary abnormalities often associated with asbestos exposure: low mean forced vital capacity percent of predicted (FVC % predicted), low mean forced expiratory volume at one second percent of predicted (FEV1 % predicted), presence of parenchymal abnormalities (40.1% with profusion scores of 1/0 or higher), and 30.5% with bilateral pleural abnormalities on chest roentgenograms. In addition, râles in two or more locations were found in 22.8% on examination of the chest, 30.6% gave a history of chronic bronchitis, and 34.8% of dyspnea grade two or higher. Calculated asbestos exposure scores, based upon participant recall, were not found to be associated with these abnormalities. The abnormal findings were not adequately explained by potential confounders such as cigarette smoking. Other notable findings in this study include the presence of smoking-adjusted decrements in pulmonary function associated with moderate profusion scores (i.e., 1/0 and 1/1) and the presence of a substantial degree of obstructive lung disease (19.2%) in this population.

A quantitative and histological study on pulmonary effects of asbestos exposure in general autopsied lungs

We demonstrated the distribution of asbestos bodies (ABs) in the lungs of 656 consecutive autopsy cases by KOH digestion method. Nine patients including one case with asbestosis had more than a thousand ABs. These patients were all blue-collar workers except the two cases without occupational history. The tissue sections for these patients revealed the constant presence of more than one or two ABs. In addition, five of these subjects had parenchymal and/or peribronchiolar fibrosis. On the basis of the result of AB counts, we selected 17 subjects for enumeration and typing of asbestos fibers (AFs). The number of AFs roughly correlated with that of ABs. However, the ratio of AFs to ABs ranged from 13 to 3,700. The fiber types in our selected subjects were almost always amphibole (crocidolite, amosite). These findings indicate that modest or secondary exposure to asbestos causes virtual asbestosis to several subjects among the general population.

Morphology of bronchogenic carcinoma in workers formerly exposed to crocidolite at Wittenoom Gorge in Western Australia

Cytology and histology material from 46 bronchogenic carcinomas occurring in ex-workers from the Wittenoom crocidolite mine and mill in Western Australia and a matched random sample of 234 other bronchogenic carcinomas occurring in Western Australia over the same period were reviewed by a single histopathologist without knowledge of asbestos exposure status. Squamous-cell carcinomas formed 45.7% of the cancers in the asbestos-exposed group but only 32.5% of the cancers in the comparison group. This difference could not be explained by differences in smoking history between the two groups of lung cancer patients or in the type of histopathological material available for review. The excess of squamous-cell cancers was observed in subjects both with and without parenchymal asbestosis.

Histologic type of lung cancer and asbestos exposure

The histologic types of lung cancer in 855 patients (747 men and 107 women) from three hospitals and one international study of insulation workers were evaluated. Of these, 196 cases had asbestos exposure. About one half of the cases were diagnosed from surgical slides and one half from autopsy slides. Squamous cell carcinoma constituted the largest percentage of tumor types and was found with the same frequency in exposed and nonexposed groups. Small cell carcinoma was found in 25% of the exposed and in 15% of the nonexposed patients. Upper lung sites were involved in about two thirds of the cases with asbestos exposure and lower lobes in the other one third. There was little difference in histologic type in cases regardless of whether upper or lower lobes were involved. Cigarette smokers who smoked until their cancer diagnosis showed no difference in histologic type by amount smoked, and slight but not statistically significant differences from ex-cigarette smokers.

Extraction of ferruginous bodies from lung tissue obtained at surgery and autopsy. Special reference to carcinoma of lung

Ferruginous bodies were extracted quantitatively from 508 patients; operated 242 with lung cancer and 94 with non-lung cancer, and autopsy 51 from hepatomas, 42 from stomach cancers, and 79 from non-cancer diseases. The bodies were divided morphologically into 4 types; 2 types may be from asbestos and the other 2 types from carbon and silicate which were very rarely found. The incidence of the bodies was the highest in hepatoma 96.8, followed by lung cancer 90.8%, non-lung cancer 80%, stomach cancer 76.2%, and non-cancer 74.2% in the years 1975-1981. Distribution of count of asbestos bodies was characteristic in patients with lung cancer, i.e. the cases who had asbestos bodies above 100/5 g of wet lung were found in 36 of 242 patients with lung cancer (14.8%) who were all smokers and 15 of 266 patients with the other diseases (5.6%) with significant difference between the two groups. Moreover, out of 14 patients who had the bodies above 300/5 g of wet lung, 9 were patients with lung cancer and also smoked heavily, and remaining 5 patients with diseases other than lung cancer consisted of 2 heavy smokers, a moderate and a mild smoker, and a non-smoker. These evidences may suggest the existence of some relation between occurrence of lung cancer and low degree of asbestos exposure with addition of smoking.

Asbestos bodies in the lung: Southampton (UK) and Wellington (New Zealand)

Two series of surgically removed and unselected necropsy lungs were examined for asbestos bodies. In the series from Southampton (UK) 30-mu sections were used and in the Wellington (New Zealand) series a modified Gold's digestion method was used for all cases, together with 30-mu sections for some. A further series of Southampton lungs was assessed by Gold's method six years after the initial study. The 30-mu section technique found asbestos bodies in 13% of Southampton men and none in women: the corresponding Wellington figures were 8% for men and nil for women. In Wellington the more sensitive digestion method found asbestos bodies in 78% of men and 63% of women. In Southampton the investigation by Gold's method found asbestos bodies in 83% of men and 74% of women. No statistically significant association was found between the number of asbestos bodies and the various types of lung carcinoma. The prevalence of asbestos in lungs removed between 1956 and 1965 did not differ significantly from its prevalence in those removed in the late 1970's. There was no significant increase in asbestos after the age of 20.

Pulmonary asbestos and dust content in East Anglia

Measurements were made of the asbestos fibre and dust content of samples from 96 surgically excised lungs; 42 necropsies on patients with lung cancer, 11 necropsies on patients with non-pulmonary malignancies, and 59 necropsies on patients without any malignant disease. The patients' ages ranged from 45 to 74 years at the time of study. None of the patients had asbestosis. The distribution of fibres and dust content of the lungs showed a log-normal distribution. There was no significant difference in fibre counts or dust content between men and women, and between lung cancer and non-cancer patients. The only group with an association with a high asbestos fibre count was four necropsy cases of pleural mesothelioma. There was no significant relationship between asbestos fibre count and dust content of the lung. The present data suggest that asbestos fibre counts below 100,000 per gram of dried lung are not related to specific asbestos disease, although in the surgical cases who were closely questioned on their residential and occupational histories most of those with fibre counts above 30,000 per gram dried lung had had occasions of definite or very likely asbestos exposure.

Fibrous ceramic aluminum silicate as an alternative to asbestos liners

The actual risk to those exposed to asbestos fibers in the dental laboratory is presently unknown. The ADA Council on Dental Materials and Devices and ADA Council on Dental Therapeutics have received encouragement from the National Institute for Occupational Safety and Health to conduct further studies, including monitoring airborne asbestos in dental laboratories. It has been suggested that no really safe threshold limit exists for airborne asbestos fibers. Low level asbestos exposure has been implicated in numerous serious diseases. Exposures as brief as 1 month have produced disease many years later. Numerous researchers have advocated the use of a safer material. Casting ring liners compound of currently available fibrous ceramic aluminum silicate are technically adequate substitutes for asbestos.

Numbers of asbestos bodies in urban patients with lung cancer and gastrointestinal cancer and in matched controls

We compared the numbers of asbestos bodies extracted from the lungs of 103 patients with lung cancer and 50 patients with gastrointestinal malignant neoplasms to the numbers of bodies extracted from lungs of control patients matched for age, sex, smoking habits, and, in some cases, occupation. All patients were urban dwellers over the age of 40 years, and none was a primary asbestos worker. No differences in the counts of asbestos bodies were observed between the tested and control populations. The numbers of asbestos bodies did correlate well with occupation; the highest counts were found in male manual laborers. We conclude that in the urban population studied herein, the numbers of asbestos bodies alone do not correlate with the presence of pulmonary or gastrointestinal carcinoma; however, uncoated asbestos fibers are also known to be present in the lung, and the possibility that such tumors may be related to the numbers of these fibers in lungs remains to be explored.

Histopathological studies on experimentally induced pulmonary, pleural and peritoneal neoplasms in mice by intraperitoneal injection of chrysotile asbestos and N-methyl-N-nitrosourethane

The cocarcinogenic effects of asbestos are presented. In lung carcinomas induced in mice, the number of carcinomas and the time of detection of the first carcinoma per tumor-bearing animals were greater and faster in the group with chrysotile plus MNU than either chrysotile or MNU alone. This suggested that chrysotile asbestos had a promoting or cocarcinogenic effect on some carcinogens in the respiratory tract. In the group treated with chryotile alone, a tumor was found in the right pleural cavity at 15 months. This tumor microscopically was similar to the biphasic form of the human diffuse mesothelioma. Microvilli, basement membrane, and junctional apparatus were seen by electron microscope, but other cytoplasmic organelles of the tumor cells were relatively scanty. Two peritoneal tumors developed in gastric and intestinal serosa at 11 and 12 months. Light and electron microscopic studies suggested that the tumors were probably myosarcomas or fibrosarcoms.

Relationship between occupations and asbestos-fibre content of the lungs in patients with pleural mesothelioma, lung cancer, and other diseases

Whitwell, F., Scott, Jean, and Grimshaw, Myra (1977).Thorax, 32, 377-386. Relationship between occupations and asbestos-fibre content of the lungs in patients with pleural mesothelioma, lung cancer, and other diseases. The light-visible asbestos-fibre content of 300 lung specimens has been measured using a potash-digestion and phase-contrast microscopy technique, and the results have been correlated with the occupations of the patients.

Among 100 pleural mesothelioma specimens were 88 where the patients had been exposed to asbestos, and in 73 of these (83%) the lung tissue contained over 100 000 asbestos fibres per gram of dried lung, and only one specimen showed less than 20 000 fibres per gram. When asbestosis was present, the lungs nearly always showed over 3 million fibres per gram.

In 100 control lungs (those without industrial disease or lung cancer) there were less than 20 000 fibres per gram of dried lung in 71% of specimens. Lungs from 100 patients with lung cancer but no industrial disease contained less than 20 000 fibres per gram of dried lung in 80% of cases. Patients with parietal pleural plaques nearly all had over 20 000 fibres per gram in their lungs.

The number of asbestos fibres found in the lungs was closely related to the occupations of the patients but not to their home environment. Patients who had lived near likely sources of atmospheric asbestos pollution did not have higher asbestos fibre counts than the rest of the patients.

It is concluded that there is a definite dose relationship between asbestos exposure and mesothelioma formation but that' `sub-asbestosis' levels of asbestos exposure do not contribute to the formation of lung cancer in those not subjected to industrial asbestos exposure.

Unsuspected exposure to asbestos and bronchogenic carcinoma

Two hundred and fifty men admitted to a thoracic surgical centre and matched controls were questioned in detail about their occupations after leaving school and their smoking habits. Of 201 men with confirmed bronchial carcinoma 58 gave a history of occupational exposure to asbestos, whereas only 29 out of 201 men matched for age and residential area who were admitted with other diseases gave such a history. This difference was statistically highly significant. The usual association of bronchial carcinoma with heavy smoking was observed, but asbestos exposure increased the risk of carcinoma whatever the level of smoking. These results are consistent with the hypothesis that asbestos exposure and the level of smoking act independently in causing bronchial carcinoma. The patients with carcinoma who had been exposed to asbestos presented on average three years earlier than those who had not been exposed. Asbestos regulations have eliminated the risk of exposure to workers in scheduled industries, so asbestos-induced diseases will probably be increasingly found among the many workers who have had incidental exposure to asbestos. It is therefore important to take a full occupational history.

Chemical carcinogenesis and experimental models using human tissues

The majority of human cancer is caused by environmental agents including chemical carcinogens. These chemical carcinogens are both naturally-occurring compounds and products of an industrialized society. Most of the environmental chemical carcinogens require enzymatic activation into electrophilic metabolites which readily react with cellular macromolecules leading, in some cases, to malignant transformation of target epithelial cells. Model systems for studying carcinogenesis in human target tissues are being developed to link investigations using experimental animals with human cancer. Metabolism of chemical carcinogens is being studied in human tissues maintained in these model systems. For example, a marked variation among individuals in their capacity to metabolize carcinogenic polynuclear aromatic hydrocarbons has been observed. This inter-individual variation may, in part, be due to genetic factors. Model systems using human tissues should be useful in several areas of cancer research including: 1) identifying environmental carcinogens, their metabolic pathways and host factors determining susceptibility; and 2) testing new methods of prophylatic intervention in populations at high risk of developing cancer.