Epidemiology of occupational asbestos-related diseases in China

In 1950s and 60s, asbestosis had been a major health hazard for asbestos exposed workers. In the late 1970s, lung cancers with or without asbestosis were found among asbestos workers. All cohort studies on asbestos workers and on chrysotile miners in China showed excess deaths from lung cancer. In a large scale of cohort study on asbestos workers, a synergistic effect was found between cigarette smoking and asbestos exposure in the production of lung cancer. There have been not so many cases of malignant mesotheliomas reported, so far. In the cohort of chrysotile miners, 4 cases of pleural mesothelioma were observed. In the large scale of cohort study on asbestos workers in 9 factories using only chrysotile only one case of pleural mesothelioma was detected for 10 years' observation. In another 2 cohort studies, 2 cases of peritoneal mesotheliomas were found, one in Shanghai asbestos factory where a small amount of crocidolite had been used in 1960s, and one in Anqing asbestos factory that was located near tremolite mine. Further study is needed especially for the relationship between exposure to Chinese chrysotile and malignant mesotheliomas.     

Role of occupational asbestos exposure in Hungarian lung cancer patients

Objective: What is the frequency of occupational asbestos exposure among patients suffering from malignant respiratory tumours and how many of these tumours are associated with asbestos in Hungary? Methods: An internationally established questionnaire with 29 questions, covering the most characteristic activities of asbestos exposure at the workplace was completed for 300 patients with respiratory malignancies, i.e. 297 patients with lung cancer and three with mesothelioma of the pleura. From the questionnaire, the smoking habits were estimated and cumulative asbestos exposure was assessed in fibre-years. Additionally, lung X-rays were classified and the national data on the incidence of malignant pleura mesothelioma were analysed. Results: A cumulative asbestos exposure of 25?fibre-years or more was detected in 11 patients with lung cancer (4%) and in each of the three patients with pleural mesothelioma (100%). In a further 72 patients (24%), cumulative occupational asbestos exposure was assessed as below 25?fibre-years (between 0.01 and 23.9?fibre-years). In this group, car and truck mechanics, and installation and construction workers using asbestos-cement were registered. Among patients with an asbestos exposure of 25?fibre-years or more, six asbestos-cement production workers were observed, among them the three mesothelioma cases. A weak but significant association between positive X-ray findings and exposure estimates could be demonstrated. Additionally, results of the lung tissue fibre counts by scanning transmission electron microscopy were available for 25 of the lung cancer patients. A good correlation was observed between the asbestos fibre counts and the assessment of cumulative asbestos exposure. In Hungary, 84 cases of pleural mesothelioma were registered in 1997 and 73 in 1998. These numbers correspond to an annual incidence of about one new case per 100,000 inhabitants older than 15?years. Conclusions: The annual incidence of lung cancer in Hungary is about 6,000. Since in our series of lung cancer patients about 4% were observed, which could be accepted as representing occupational disease because of a cumulative exposure to 25?fibre-years or more, the annual asbestos related lung tumour incidences may be estimated to be approximately 150 or more. The proportion of nearly two estimated cases of lung cancer per case of pleural mesothelioma corresponds to international experience. Up to now, lung cancer cases only exceptionally have been registered as occupational diseases, i.e. they were seriously under-diagnosed in Hungary. For improving this situation, diagnostic assistance by a self-interview with a questionnaire covering the working history for all newly diagnosed lung cancer patients would be helpful.     

Historical cohort study of US man-made vitreous fiber production workers: II. Mortality from mesothelioma

As part of our ongoing mortality surveillance program for the US man-made vitreous fiber (MMVF) industry, we examined mortality from malignant mesothelioma using data from our 1989 follow-up of 3478 rock/slag wool workers and our 1992 follow-up of 32,110 fiberglass workers. A manual search of death certificates for 1011 rock/slag wool workers and 9060 fiberglass workers revealed only 10 death certificates with any mention of the word "mesothelioma." A subsequent review of medical records and pathology specimens for 3 of the 10 workers deemed two deaths as definitely not due to mesothelioma and one as having a 50% chance of being caused by mesothelioma. Two other deaths, for which only medical records were available, were given less than a 50% chance of being due to mesothelioma. Eight of the 10 decedents had potential occupational asbestos exposure inside or outside the MMVF industry. We also estimated the mortality risk from malignant mesothelioma in the cohort using two cause-of-death categorizations that included both malignant and benign coding rubrics. Using the more comprehensive scheme, we observed overall deficits in deaths among the total cohort and fiberglass workers and an overall excess among rock/slag wool workers. The excess in respiratory system cancer is largely a reflection of elevated lung cancer risks that we attributed mainly to confounding by smoking, to exposures outside the MMVF industry to agents such as asbestos, or to one or more of the several co-exposures present in many of the study plants (including asbestos). The second scheme, which focused on pleural mesothelioma in time periods when specific malignant mesothelioma coding rubrics were available, classified only one cohort death as being caused by malignant mesothelioma, compared with 2.19 expected deaths (local county comparison). We conclude that the overall mortality risk from malignant mesothelioma does not seem to be elevated in the US MMVF cohort.     

Malignant mesothelioma from neighborhood exposure to anthophyllite asbestos

BACKGROUND: Anthophyllite asbestos has been reported to cause asbestosis, lung cancer, mesothelioma, and pleural plaques in occupationally exposed workers. Anthophyllite has also been associated with pleural plaques in Finland and Japan among those who live near mines and mills and have neighborhood or environmental exposure. METHODS: We evaluated a 38-year-old patient with pleural mesothelioma who lived, attended school, and delivered newspapers near a manufacturing facility that used exclusively anthophyllite asbestos fiber from ages 8-17 years. He had no work exposure to asbestos. RESULTS: The pleural mesothelioma was an epithelial type with tubulopapillary structures and was treated with an extrapleural pneumonectomy followed by radiation therapy. The malignant cells were positive by immunohistochemistry for cytokeratin but negative for carcinoembryonic antigen, S100, B72.3, and leu M1 antigen. Anthophyllite fibers were > 5 microm in length in lung tissue compared to 3 microm from a general population study. CONCLUSIONS: Anthophyllite asbestos has been associated with neighborhood environmental exposure and pleural plaques; we now report a neighborhood exposure and pleural mesothelioma.     

Non-malignant asbestos diseases in workers in an electrochemical plant.

The prevalence of non-malignant asbestos related disorders was studied in a group of men who had been subjected to different levels of asbestos exposure when working at an electrochemical plant producing nitric acid sometime between 1928 and 1970. There were 153 men eligible for an initial clinical examination in 1979-80 and that group has been followed up to 1985. Among the cohort members the "accumulated prevalence" of lung fibrosis alone or in combination with pleural plaques and of "pleural plaques only" was 24.2% and 24.8% respectively. The subgroup with the heaviest exposure had a total prevalence of asbestos related disorders of 82.5%. Only study subjects with lung fibrosis had statistically significant increased prevalences of respiratory symptoms. All subgroups from the study population, however, had mean spirometric values under the age, height, and smoking specific predicted means. Subjects with heavy asbestos exposure and current smoking had a prevalence of three or more respiratory symptoms of 28.8% compared with 5.6% among lightly exposed never smokers. Pleural crepitations at chest auscultation were more prevalent among subjects with radiologically visible asbestos related disorders than among study subjects with normal chest x ray films. During the follow up from 1980 to 1985, three cases of lung cancer, two of pleural malignant mesothelioma, and one of stomach cancer were found among the cohort members.     

Non-malignant asbestos diseases in workers in an electrochemical plant

The prevalence of non-malignant asbestos related disorders was studied in a group of men who had been subjected to different levels of asbestos exposure when working at an electrochemical plant producing nitric acid sometime between 1928 and 1970. There were 153 men eligible for an initial clinical examination in 1979-80 and that group has been followed up to 1985. Among the cohort members the "accumulated prevalence" of lung fibrosis alone or in combination with pleural plaques and of "pleural plaques only" was 24.2% and 24.8% respectively. The subgroup with the heaviest exposure had a total prevalence of asbestos related disorders of 82.5%. Only study subjects with lung fibrosis had statistically significant increased prevalences of respiratory symptoms. All subgroups from the study population, however, had mean spirometric values under the age, height, and smoking specific predicted means. Subjects with heavy asbestos exposure and current smoking had a prevalence of three or more respiratory symptoms of 28.8% compared with 5.6% among lightly exposed never smokers. Pleural crepitations at chest auscultation were more prevalent among subjects with radiologically visible asbestos related disorders than among study subjects with normal chest x ray films. During the follow up from 1980 to 1985, three cases of lung cancer, two of pleural malignant mesothelioma, and one of stomach cancer were found among the cohort members.     

Cohort mortality study of women compensated for asbestosis in Italy.

BACKGROUND: The carcinogenic effect of asbestos is accepted for lung cancer and mesothelioma, while conflicting opinions exist for other cancer sites. The aim of the present investigation is to study cause-specific mortality of women compensated for asbestosis who had certainly been exposed to high levels of asbestos fibers. METHODS: The cause-specific mortality of all Italian women compensated for asbestosis and alive December 31, 1979, was investigated through October 30, 1997. In the total cohort, which included 631 subjects, 277 deaths occurred. Cause-specific SMRs (Standardized Mortality Ratio) were computed using the national rates for comparison. RESULTS: A significantly increased mortality for all diseases related to asbestos exposure was observed. Mortality for all causes, all neoplasms, lung cancer, uterine cancer, ovarian cancer, and non-neoplastic respiratory diseases was significantly increased. Separate analyses for textile (n = 276) and asbestos-cement (n = 278) workers were performed. Women employed in the textile industry, mainly exposed to chrysotile, who are compensated at a younger age, showed higher SMRs for lung cancer and asbestosis. Women in the asbestos-cement industry, mainly exposed to crocidolite containing asbestos mixtures, experienced higher mortality for pleural malignancies. CONCLUSIONS: The role of asbestos exposure in the development of gastrointestinal and genital neoplasms is discussed.     

The prevalence of pleural plaques and/or pulmonary changes among construction workers in Okayama, Japan

BACKGROUND: Since asbestos has been widely used in Japanese building materials since 1960s, a large number of Japanese construction workers may be exposed to asbestos occupationally. METHODS: Among 2951 construction workers in Okayama, Japan, the prevalence of asbestos-induced pleural or pulmonary changes was examined by screening chest x-rays; these findings were confirmed by computed tomography (CT) scanning of the chest. RESULTS: Among 2951 construction workers, 168 (5.7%) were found to have significant findings for pleural plaque or pulmonary changes on chest x-ray. Seventy-four had both pleural plaque and asbestosis, 85 pleural plaques alone, and 9 asbestosis alone. In 11 subjects, pleural plaques were suggested by chest x-ray, but neither pleural plaque nor asbestosis was demonstrated by chest CT. Honeycombing as one of the characteristic findings of asbestosis was found in 29 subjects. Others showed subpleural spots or curvilinear shadow, which suggested the early stage of asbestosis. The occupations of these workers were carpenters (64), plasterers (27), and concrete board cutters (14). About 30% of the workers with these findings were aware that they were handling asbestos in activities such as installation of asbestos boards, and/or asbestos spraying. CONCLUSIONS: As the incidence of malignant mesothelioma and primary lung cancer associated with asbestos exposure are high, screening by chest CT is necessary for detecting asbestos-induced pulmonary and/or pleural lesions. Education for protection such as telling about the presence of asbestos in building materials is also necessary.     

Chrysotile asbestos and health in Zimbabwe: I. Analysis of miners and millers compensated for asbestos-related diseases since independence (1980)

Data on the health effects caused by locally mined chrysotile asbestos in Zimbabwe have been very limited. The prevailing local view has been that risk is minimal. In this report we critically reassess the cases of 51 individuals with asbestos exposure who have been compensated by the Central Pneumoconiosis Bureau since independence in 1980. Results demonstrate that the major health risks of exposure reported elsewhere--morbid asbestosis, nonmalignant pleural disease, malignant mesothelioma, and lung cancer--all occur in Zimbabwe, at least among workers in the asbestos mines and mills. It is concluded that further investigation and control measures in the industry are warranted.     

Cancer mortality among workers exposed to amphibole-free chrysotile asbestos.

The issue of whether exposure to chrysotile asbestos alone, without contamination from amphibole asbestos, causes lung cancer and mesothelioma was investigated in a 25-year longitudinal study (1972-1996) in Chongqin, China. The study cohort comprised 515 male asbestos plant workers exposed to chrysotile only; the control cohort included 650 non-dust-exposed workers. The results of analysis in which the proportional hazards model was used indicated that mortality due to all causes, all cancers, and lung cancer was related to asbestos exposure; the relative risks, adjusted for age and smoking, were 2.9, 4.3, and 6.6, respectively. Fiber concentrations in the raw material section and the textile section of the plant were 7.6 and 4.5 fibers/ml, respectively. Because of differences between the study and control plants, the authors also compared various sections of the asbestos plant that had different levels of dust exposure. The adjusted relative risk of lung cancer was 8.1 for workers exposed to high versus low levels of asbestos. Two cases of malignant mesothelioma, one pleural and the other peritoneal, were found in the asbestos cohort. These results suggest that heavy exposure to pure chrysotile asbestos alone, with negligible amphibole contamination, can cause lung cancer and malignant mesothelioma in exposed workers.     

Health effects of asbestos exposure in humans: a quantitative assessment

Asbestos causes four diseases in humans: Lung fibrosis (asbestosis) follows heavy exposure and, in industrialized countries, is mainly a relic of past working conditions. The risk of pleural fibrosis and plaques is likely to be linearly dependent from time since first exposure and is present for all types of asbestos fibres. The diagnostic uncertainties regarding pleural plaques and the substantial degree of misclassification make it difficult to precisely estimate the shape of the dose-response relationship. The risk of lung cancer seems to be linearly related to cumulative asbestos exposure, with an estimated increase in risk of 1% for each fibre/ml-year of exposure. All fibre types seem to exert a similar effect on lung cancer risk; a multiplicative interaction with tobacco smoking has been suggested. Pleural mesothelioma is a malignant neoplasm which is specifically associated with asbestos exposure: the risk is linked with the cubic power of time since first exposure, after allowing for a latency period of 10 years, and depends on the fibre type, as the risk is about three times higher for amphiboles as compared to chrysotile. Environmental exposure to asbestos is also associated with mesothelioma risk.     

Estimating the number of asbestos-related lung cancer deaths in Great Britain from 1980 to 2000

INTRODUCTION: Inhalation of asbestos fibres is known to cause two main kinds of cancer-mesothelioma and lung cancer. While the vast majority of mesothelioma cases are generally accepted as being caused by asbestos, the proportion of asbestos-related lung cancers is less clear and cannot be determined directly because cases are not clinically distinguishable from those due to other causes. The aim of this study was to estimate the number of asbestos-related lung cancers among males by modelling their relative lung cancer mortality among occupations within Great Britain in terms of smoking habits, mesothelioma mortality (as an index of asbestos exposure) and occupation type (as a proxy for socio-economic factors). METHODS: Proportional mortality ratios for lung cancer and mesothelioma for the 20-year period from 1980 to 2000 (excluding 1981) were calculated for occupational groups. Smoking indicators were developed from three General Household Surveys carried out during the 1980s and 1990s. Poisson regression models were used to estimate the number of asbestos-related lung cancers by estimating the number of lung cancer deaths in each occupation assuming no asbestos exposure and subtracting this from the actual predicted number of lung cancer deaths. RESULTS: The effect of asbestos exposure in predicting lung cancer mortality was weak in comparison to smoking habits and occupation type. The proportion of current smokers in occupational groups and average age at which they started smoking were particularly important factors. Our estimate of the number of asbestos-related lung cancers was between two-thirds and one death for every mesothelioma death: equivalent to between 11 500 and 16 500 deaths during the time period studied. CONCLUSIONS: Asbestos-related lung cancer is likely to have accounted for 2-3% of all lung cancer deaths among males in Great Britain over the last two decades of the 20th century. Asbestos-related lung cancers are likely to remain an important component of the total number of lung cancer deaths in the future as part of the legacy of past asbestos exposures in occupational settings.     

Asbestos related diseases in Italy: an integrated approach to identify unexpected professional or environmental exposure risks at municipal level

PURPOSE: Past intensive use of asbestos has implied severe public health consequences. Spatial distribution of deaths from malignant mesothelioma and of compensated cases for asbestos related diseases in Italy were compared to identify unexpected sources of asbestos exposure. METHODS: Mortality for malignant mesothelioma at municipal level and geographical clusters of compensated cases for asbestos related diseases, as proxy of industrial asbestos exposure, were identified in the period 1988-2001. RESULTS: Municipalities with at least four mesothelioma deaths and a statistically significant mortality excess were 148; and 53 out of them had no compensated case for asbestos-related diseases. Finally 22 of these lay outside of any aforementioned cluster, thus suggestive of a possible unrecognized exposure. CONCLUSIONS: Availability long-term national figures and the different etiology of asbestos related diseases are the key features of this exercise that was applied to Italy, but can be replicated wherever registration systems of diseases related to long term exposure to asbestos are available.     

Effect of smoking on pleural thickening in asbestos workers.

It is well known that an interaction exists between smoking and exposure to asbestos in the occurrence of lung cancer, whereas occurrence of malignant mesothelioma has not been related to smoking. In the case of pleural thickening related to asbestos, there is a disagreement in previous studies as to the effect of smoking. This could be because the diagnosis of pleural changes has a subjective element. Taking this into account, in the present work the maximum width of the pleura was used as an index of pleural changes. Study subjects were 134 asbestos workers of a brake manufacturing company who had received medical checks in 1978 and in 1990. The maximum width of the pleura on the chest x ray films of the workers was measured by two examiners who did not know the year of examination or smoking state of the worker. A general linear model was applied to analyse the effects of smoking, the year of examination, age, and duration of exposure to asbestos. The difference between maximum widths measured in 1978 and 1990 suggested chronological progression. The increase in width during the 12 years, however, did not differ significantly between smokers and nonsmokers. This suggests that smoking does not significantly increase pleural thickening in asbestos workers.     

Malignant pleural cancers mortality and compensated cases for asbestos related diseases in Lazio municipalities (1980-2001)

BACKGROUND: Occupational exposure to asbestos has been widely reported in the Region, but a high risk for non-occupational and environmental contaminations have also been documented. OBJECTIVES: To describe the geographical distribution ofpleural cancer deaths and compensated asbestosis cases from 1980 to 2001 in the Lazio Region. METHODS: For each municipality Standardized Mortality Ratios (SMRs) for pleural cancer and Standardized Incidence Ratios (SIRs) for asbestosis were estimated. Expected cases were estimated from age and gender specific rates in Lazio. SatScan software was used to identify clusters and to verf;j their statistical significance. RESULTS: 789 deaths from pleural cancer (495 males and 294 females) occurred in Lazio from 1980 to 2001. The standardized mortality rate per 100.000 inhabitants is 0,74 (0,95 for males and 0,54 for females). The main excess mortality from pleural cancer occurred in the municipalities of Civitavecchia (SMR: 269,9; 95% CI: 164,9 - 416,8), Colleferro (SMR: 304,9; 95% CI: 139,4-578,8) and Rocca Priora (SMR: 379,2; 95% CI: 103,3-970,9). Significant SIRs for compensated asbestosis cases were found in the industrial areas of the Naples-Rome highway and in the shipyard area of Civitavecchia. Nofemale compensated cases were found. The most important clusters were identified in the municipality of Civitavecchia for pleural cancer (p-value = 0,117) and in the Colleferro industrial area for compensated asbestosis cases (p-value = 0,001). CONCLUSIONS: Epidemiological surveillance of incident cases of malignant mesothelioma in the Lazio Region and the investigation of modalities of asbestos exposure are urgently needed for prevention of occupational diseases.     

Environmental exposure to tremolite and respiratory cancer in New Caledonia: a case-control study

A case-control study on respiratory cancers was conducted in New Caledonia (South Pacific), where a high incidence of malignant pleural mesothelioma had been observed. The disease pattern suggested an environmental exposure to asbestos. The first results showed that, in some areas, tremolite asbestos derived from local outcroppings was used as whitewash (locally named "p?"). All cases diagnosed between 1993 and 1995 (including 15 pleural mesotheliomas, 228 lung cancers, and 23 laryngeal cancers) and 305 controls were included in the study. Detailed information on past or present use of the whitewash, residential history, smoking, diet, and occupation was collected. The risk of mesothelioma was strongly associated with the use of the whitewash (odds ratio (OR) = 40.9; 95% confidence interval (CI): 5.15, 325). All Melanesian cases had been exposed. Among Melanesian women, exposure to the whitewash was associated with an increased risk of lung cancer (OR = 4.89; 95% CI: 1.13, 21.2), and smokers exposed to po had an approximately ninefold risk (OR = 9.26; 95% CI: 1.72, 49.7) compared with women who never smoked and had never used the whitewash. In contrast, no association was noted between exposure to p? and lung cancer risk among Melanesian men, probably because of lower exposure levels. Among non-Melanesians, the numbers of exposed subjects were too small to assess the effect of exposure to po. There was no indication of elevated risks for the other cancer sites.     

Diffuse malignant pleural mesothelioma in an urban hospital: clinical spectrum and trend in incidence over time

This retrospective analysis reviews the clinical experience of a major urban referral hospital with diffuse malignant pleural mesothelioma during the 14-year period from 1973 through 1986. Seventy-five cases of definite or equivocal mesothelioma were identified. There were four cases of primary malignant peritoneal mesothelioma, seven cases of benign fibrous mesothelioma, and 64 cases of diffuse malignant pleural mesothelioma. In 43 cases (67%) of diffuse malignant pleural mesothelioma, there was historic evidence of asbestos exposure. In 21 cases (33%), there was no known history of asbestos exposure. An increase in annual incidence of diffuse malignant pleural mesothelioma was observed over the study period, from three cases in 1973 to ten cases in 1986. Despite greater awareness of this disease, the diagnosis remains a difficult one to establish given the nonspecific symptoms, signs and radiographic appearance, variable histologic appearance, and poor diagnostic sensitivity and specificity of thoracentesis and closed pleural biopsy. Thoracotomy, thoracoscopy, and CT-guided needle biopsies gave higher yields and are the diagnostic measures of choice when diffuse malignant pleural mesothelioma is suspected.     

The Handling of Workmen’s Compensation Claims

Few data exist concerning the comparative neoplastic potential in man of the several kinds of asbestos. In particular, there has been no evidence concerning whether the amosite variety is carcinogenic. The matter is of practical importance, since amosite use in the United States has sharply increased. The mortality experience of a group of 230 men previously employed in an amosite asbestos factory was studied during the years 1960 through 1971. Total deaths were more than twice the number anticipated: 46.4 were expected, and 105 occurred. Some 14 deaths were due to asbestosis. Both lung cancer and mesothelioma were found in considerable excess. Two or three deaths from lung cancer were expected, and 25 occurred. There were five deaths from mesothelioma. Occupational exposure to amosite asbestos can be associated with serious cancer hazard; its continued industrial use requires rigorous control.     

A proportional study of cancer registrations of dockyard workers.

Evidence of an occupational effect due to asbestos exposure was sought by comparing cancer registrations for dockyard workers with those for Plymouth men in the same age groups for 1960-69. The results show a significant excess of pleural tumours in the dockyard group but no significant excesses at other sites. Registrations for pleural mesothelioma were recorded for men with many dockyard occupations and the observed mean interval between first exposure to asbestos and registration for a pleural tumour (37.6 years) indicates that cases of pleural mesothelioma may be expected to occur among these workers for many years, even though crocidolite is no longer used in naval ships. A trend of increasing annual excess of stomach and gastrointestinal registrations was observed in the dockyard group. No cases of peritoneal mesothelioma were recorded but it is likely that some did occur which were diagnosed as cancers arising from other sites. This may account for some of the excess of gastrointestinal registrations.     

A proportional study of cancer registrations of dockyard workers.

Evidence of an occupational effect due to asbestos exposure was sought by comparing cancer registrations for dockyard workers with those for Plymouth men in the same age groups for 1960-69. The results show a significant excess of pleural tumours in the dockyard group but no significant excesses at other sites. Registrations for pleural mesothelioma were recorded for men with many dockyard occupations and the observed mean interval between first exposure to asbestos and registration for a pleural tumour (37.6 years) indicates that cases of pleural mesothelioma may be expected to occur among these workers for many years, even though crocidolite is no longer used in naval ships. A trend of increasing annual excess of stomach and gastrointestinal registrations was observed in the dockyard group. No cases of peritoneal mesothelioma were recorded but it is likely that some did occur which were diagnosed as cancers arising from other sites. This may account for some of the excess of gastrointestinal registrations.