Thirty-two cases of mesothelioma in Victoria, Australia: a retrospective survey related to occupational asbestos exposure.

Mesotheliomas have been reported in four states in Australia. Crocidolite has been mined and milled at Wittenoom in West Australia where five cases of mesothelioma were reported after exposure of high intensity. The 32 cases of mesothelioma reported in this paper occurred during a period of 11 years in Victoria; 29 were pleural and three peritoneal. There were 22 autopsies. End occupations were misleading in 66% of cases. Two of the three subjects with peritoneal mesothelioma were siblings, and there was no evidence of occupational or other exposure to asbestos in either. There was a significant prevalence of pulmonary asbestos bodies in the tumour series as compared with an unselected consecutive series of 200 routine autopsies (0.01 greater than P greater than 0.001). The occupational history was as effective a method of assessing 'true' asbestos exposure as the pulmonary asbestos body count. Five cases had had a duration of exposure of one year or less, but they had had heavy exposure. The latent interval before tumour development was 25 years or longer in each case. There was no known exposure to asbestos in five cases (16%). The rare association of mesothelioma with types of asbestos other than crocikolite may not exist and could be explicable on the basis of the proportion (16%) of these tumours arising randomly in the population.     

Mesothelioma in South Africa, 1976-84: incidence and case characteristics

Malignant mesothelioma is a rare tumour known to be associated with prior exposure to asbestos. Previous studies have described the occupational and clinical features of cases of mesothelioma in the Republic of South Africa (RSA) but none has set out to determine incidence of this disease. To estimate incidence, a case register was compiled for 1976-84 by contacting all medical practitioners and institutions likely to have seen cases of mesothelioma in this period; demographic, diagnostic and exposure details were sought. Cases were accepted if they provided evidence of histological diagnosis of mesothelioma. Fifty-two per cent of 1347 cases identified were in whites, 31% in blacks, 16% in coloureds and 1% in Asians. Seventy-three per cent of cases occurred in males. The majority of whites were aged 51-70 years, while the majority in other race groups were aged 41-60 years. The ratio of only pleural to only peritoneal mesothelioma was 11:1, although there were marked differences by race. Eighty-five per cent of males with exposure information available had prior exposure to asbestos, mostly occupational. A similar proportion of women had contact with asbestos but mostly through other types of exposure. Standardized incidence rates per million population aged 15 years and over were calculated for sex-race subgroups and were highest in white males (32.9 per million per year, 95% Cl 22.7-46.4), coloured males (24.8 per million per year, 95% Cl 16.2-36.9) and coloured females (13.9 per million per year, 95% Cl 7.7-23.5). These incidence rates are amongst the highest ever reported for a national population. Age-specific standardized incidence rates were highest in white males (over 100 per million per year in men over 55 years). Reasons for the differing rates by population group are likely to include differential access to health services. More rigorous control of asbestos exposure in the RSA is recommended.     

Histological types of malignant mesothelioma and asbestos exposure.

The Los Angeles County Cancer Surveillance Program abstracts hospital pathology records on almost all cases of cancer occurring in the county. Those cases of pleural and peritoneal mesothelioma that occurred between 1972 and 1978 were identified. Occupational histories were obtained from interviews, and the histopathology of the tumours was reviewed by a member of a mesothelioma reference panel who was unaware of the exposure histories. The relation of asbestos exposure to the three histological types of mesothelioma (epithelial, mesenchymal, and mixed) was studied among the 29 cases for whom occupational histories were available and who were also considered to have histopathology consistent with mesothelioma. The proportion of cases exposed to asbestos was high for both the epithelial (11/17, 65%) and mixed histological types (6/11, 55%). The single case of mesothelioma classified as a mesenchymal type was also exposed to asbestos. Cases who had worked in shipyards were represented in each of the three groups. In cases who had worked in asbestos production and manufacture an exclusively epithelial type of tumour was observed. In cases who had worked as insulators or in heating trades the histological type was predominantly (3/4) mixed. These data do not support the hypothesis that any specific histological type of mesothelioma is especially related to asbestos exposure.     

Histological types of malignant mesothelioma and asbestos exposure

The Los Angeles County Cancer Surveillance Program abstracts hospital pathology records on almost all cases of cancer occurring in the county. Those cases of pleural and peritoneal mesothelioma that occurred between 1972 and 1978 were identified. Occupational histories were obtained from interviews, and the histopathology of the tumours was reviewed by a member of a mesothelioma reference panel who was unaware of the exposure histories. The relation of asbestos exposure to the three histological types of mesothelioma (epithelial, mesenchymal, and mixed) was studied among the 29 cases for whom occupational histories were available and who were also considered to have histopathology consistent with mesothelioma. The proportion of cases exposed to asbestos was high for both the epithelial (11/17, 65%) and mixed histological types (6/11, 55%). The single case of mesothelioma classified as a mesenchymal type was also exposed to asbestos. Cases who had worked in shipyards were represented in each of the three groups. In cases who had worked in asbestos production and manufacture an exclusively epithelial type of tumour was observed. In cases who had worked as insulators or in heating trades the histological type was predominantly (3/4) mixed. These data do not support the hypothesis that any specific histological type of mesothelioma is especially related to asbestos exposure.     

Malignant mesothelioma in Australia, 1945-2000

BACKGROUND: Australia has maintained a total national malignant mesothelioma case register since 1980. There has been a marked increase in the incidence of mesothelioma in the last 20 years. Currently 450-600 cases are notified annually in a population of 20 million. While the history of the Wittenoom (Western Australia) crocidolite mine and its aftermath is well known, these cases comprise only 5% of the total. This study describes the incidence of mesothelioma in Australia from 1945 to 2000. METHODS: Using register data, time trends in mesothelioma incidence were calculated. Analyses of incidence are reported by age, sex, anatomical site, and state of notification. Associations with occupational and environmental asbestos exposure histories are described. Lung fiber content measurements were made on a subset of cases. RESULTS: Australia has had 6,329 cases of mesothelioma from 1 January 1945 to 31 December 2000. (A further 620 cases were notified in the period from 1 January 2001 to 31 October 2001.) Annual incidence rates for Australia per million population > or = 20 years (1997) were: male, 59.8; female, 10.9; total, 35.4. Incidence rates have been continually increasing and are the highest reported national rates in the world. While Western Australia has the highest rate (1997 total rate, 52.8), most cases arise from the two most populous eastern states, New South Wales and Victoria. In 88% (male 90%, female 61%) of cases, a history of asbestos exposure was obtained. Exposures occurred in a wide variety of occupational and environmental circumstances. In 80% of cases with no history of exposure, TEM lung asbestos fiber counts > 200,000 fibers > 2 microm length per gm dry lung were obtained, suggesting unrecognized exposure. CONCLUSIONS: Australia's high incidence of mesothelioma is related to high past asbestos use, of all fiber types, in a wide variety of occupational and environmental settings. The number of cases in total is expected to be about 18,000 by 2020, with about 11,000 yet to appear.     

National epidemiologic surveillance systems of asbestos-related disease and the exposed workers register

INTRODUCTION: Italy was the main European producer of asbestos for most of the 20th century and raw asbestos imports wee also significant until the 1990's; there was a mean delay of about ten years in the pattern of asbestos consumption in Italy compared with the USA, Australia, UK and Scandinavian countries. METHODS: A national surveillance system (ReNaM) was implemented to identify cases of mesothelioma and investigate the modalities of asbestos exposure. A register of exposed workers and a database of companies presumably involved in the asbestos exposure problem was also developed. ReNaM has a regional structure and an operative centres (COR) have been established in 16 Italian regions. RESULTS: The ReNaM database currently contains more than 5,000 mesothelioma cases and for 3,500 of these exposure modalities have been defined. Cases of pleural mesothelioma represent 93% of the total but there were also 334 cases of peritoneal mesothelioma, 15 of the pericardium and 14 of the tunica vaginalis of the testicle. Cases with ascertained exposure are thus distributed: 67.4% occupational exposure (ascertained, probable, possible), 4.3% domestic, 4.2% environmental and 1.3% hobby-related exposure, totalling 77.2%; 22.8% had unlikely or unknown exposure. The latency period is very long: on average 43.6 years. The register of asbestos-exposed workers contains figures on exposed workers notified to ISPESL up to 2004 and refers to the exposure period 1993-2003. The data registered cover 160 firms and about 700 workers. CONCLUSIONS: A national, coordinated and uniform epidemiological surveillance system of cases of mesothelioma and the definition of asbestos exposure through active research is extremely important in identifying unexpected contaminating sources. The register of asbestos-exposed workers allows risk to be monitored and protection measures to be implemented.     

Asbestos and peritoneal mesothelioma among college-educated men

The proportion of peritoneal mesotheliomas among all mesotheliomas has been decreasing, leading some to suggest that peritoneal mesothelioma occurs only after high levels of exposure to asbestos. To investigate the relationship between asbestos exposure and the development of peritoneal mesothelioma, a case-control study examined 40 cases of primary peritoneal mesothelioma from a single institution. This series differed from previous reports in that 75% of the cases and controls had attended college. Results show an odds ratio of 6.6 for asbestos exposure among this group of primary peritoneal mesothelioma cases with relatively slight asbestos exposures.     

Asbestos and Peritoneal Mesothelioma among College-educated Men

Abstract

The proportion of peritoneal mesotheliomas among all mesotheliomas has been decreasing, leading some to suggest that peritoneal mesothelioma occurs only after high levels of exposure to asbestos. To investigate the relationship between asbestos exposure and the development of peritoneal mesothelioma, a case–control study examined 40 cases of primary peritoneal mesothelioma from a single institution. This series differed from previous reports in that 75% of the cases and controls had attended college. Results show an odds ratio of 6.6 for asbestos exposure among this group of primary peritoneal mesothelioma cases with relatively slight asbestos exposures.     

Mineral fibre analysis and routes of exposure to asbestos in the development of mesothelioma in an English region

OBJECTIVES: To compare the concentrations of inorganic fibres in the lungs in cases of mesothelioma and controls: to determine whether concentrations of retained asbestos fibres differ with the different exposures identified from interview; and to investigate the existence of a cut off point in concentrations of asbestos fibres that indicates occupational exposure. METHODS: Case-control study; 147 confirmed cases of mesothelioma and 122 controls identified from deaths occurring in four districts of Yorkshire between 1979 and 1991. Surviving relatives were interviewed to determine lifetime exposure history to asbestos. Mineral fibre analysis was carried out on lung tissue from postmortem examinations. RESULTS: Odds on high concentrations of retained asbestos fibres were greater in cases than controls. After excluding subjects with occupational and paraoccupational exposure, the odds on high concentrations were still greater in cases than controls, but only significantly so for amphiboles. There was only a weak relation between probability of occupational exposure to asbestos and concentrations of retained asbestos fibres, and no significant difference in fibre concentrations was found between subjects who had been exposed to asbestos through different routes: these comparisons were only based on small groups. There was considerable overlap in concentrations of retained asbestos fibres between cases and controls with and without histories of occupational exposure. CONCLUSIONS: The study has confirmed previous results of higher concentrations of asbestos fibres in cases than controls, and has shown that this is still found in subjects with little evidence of occupational and para-occupational exposure. The overlap in concentrations of retained asbestos for different groups of subjects did not suggest a clear cut of value.

 

     

Malignant mesothelioma: attributable risk of asbestos exposure.

OBJECTIVES--To evaluate a case-control study of malignant mesothelioma through patterns of exposure to asbestos based upon information from telephone interviews with next of kin. METHODS--Potential cases, identified from medical files and death certificates, included all people diagnosed with malignant mesothelioma and registered during 1975-1980 by the Los Angeles County Cancer Surveillance Program, the New York State Cancer Registry (excluding New York City), and 39 large Veterans Administration hospitals. Cases whose diagnosis was confirmed in a special pathology review as definite or probable mesothelioma (n = 208) were included in the analysis. Controls (n = 533) had died of other causes, excluding cancer, respiratory disease, suicide, or violence. Direct exposure to asbestos was determined from responses to three types of questions: specific queries as to any exposure to asbestos; occupational or non-vocational participation in any of nine specific activities thought to entail exposure to asbestos; and analysis of life-time work histories. Indirect exposures were assessed through residential histories and reported contact with family members exposed to asbestos. RESULTS--Among men with pleural mesothelioma the attributable risk (AR) for exposure to asbestos was 88% (95% confidence interval (95% CI) 76-95%). For men, the AR of peritoneal cancer was 58% (95% CI 20-89%). For women (both sites combined), the AR was 23% (95% CI 3-72%). The large differences in AR by sex are compatible with the explanations: a lower background incidence rate in women, lower exposure to asbestos, and greater misclassification among women. CONCLUSIONS--Most of the pleural and peritoneal mesotheliomas in the men studied were attributable to exposure to asbestos. The situation in women was less definitive.     

Asbestos fiber analysis in 27 malignant mesothelioma cases.

The asbestos body counts per 5 gm wet lung tissue in 27 (23 pleural and 4 peritoneal) malignant mesothelioma cases derived from 19 autopsy and 8 surgical cases were, according to our own criteria, low level exposure in 13 cases (48.2%), moderate level exposure in 2 cases (7.4%), and high level exposure in 12 cases (44.4%). In our previous study on 235 consecutive autopsy cases, the low level exposure was considered to be environmental, the moderate level was secondary or blue collar, and the high level was occupational. In the present study, about half of the cases examined (44.4%, high level exposure) are closely related to some occupational asbestos exposure and the other half (48.2%) to environmental exposure. The type and size of asbestos fibers from the 12 cases of high level exposure were analyzed and the characteristics were compared with those of cases of low level exposure without lung cancer or mesothelioma. Most fibers analyzed (98%) were longer than 5 microns and thicker than 0.10 micron by our counting rules. In the control group, predominant fibers were tremolite or actinolite. In all the 11 pleural mesothelioma cases, the content of amosite fibers was significantly higher than in the controls. In one case of peritoneal mesothelioma, incipient asbestosis was found and the predominant fibers were crocidolite. It is suggested that the presence of amosite and crocidolite is linked to mesothelioma. The mean lengths of amosite and crocidolite, as detected by our resolution capabilities, were 36.0 and 20.9 microns, and the mean diameters were 0.51 and 0.27 micron, respectively. Both amosite and crocidolite fibers had high aspect ratios (94.2 and 115.4).     

Malignant mesothelioma in Australia, 1945-2002

Using register data, time trends in mesothelioma incidence in Australia from 1945 to 2002 were calculated. Incidences are reported by age, sex, anatomic site, and state of notification. Associations with occupational and environmental asbestos exposure histories and lifetime risks in different exposure categories were investigated. Lung-fiber content was measured in a subset of cases. Australia had 7,027 cases from 1945 to 2001, with 488 more in January 2002 through June 2003. Incidence rates for Australia per million population > or = 20 years old (1999) were: male 53.3; female 10.2; total 31.8. Rates have continually increased and are the highest reported national rates in the world. Western Australia had the highest rate (1999 total 47.7), but most cases arose from the two most populous eastern states, New South Wales and Victoria. In 88% of cases (male 90%, female 61%), histories of asbestos exposures were obtained. In 80% of cases with no history of exposure, TEM lung asbestos fiber counts > 200,000 fibers > 2 microm length/g dry lung were obtained, suggesting unrecognized exposure. Australia's high incidence of mesothelioma is related to high past asbestos use, of all fiber types, in a wide variety of settings. The number of cases is expected to be about 18,000 by 2020, with about 11,000 yet to appear.     

Asbestos-related disease associated with exposure to asbestiform tremolite

Tremolite is nearly ubiquitous and represents the most common amphibole fiber in the lungs of urbanites. Tremolite asbestos is not mined or used commercially but is a frequent contaminant of chrysotile asbestos, vermiculite, and talc. Therefore, individuals exposed to these materials or to end-products containing these materials may be exposed to tremolite. We have had the opportunity to do asbestos body counts and mineral fiber analysis on pulmonary tissue from five mesothelioma cases and two asbestosis cases with pulmonary tremolite burdens greater than background levels. There were no uncoated amosite or crocidolite fibers detected in any of these cases. Three patients were occupationally exposed to chrysotile asbestos; two patients had environmental exposures (one to vermiculite and one to chrysotile and talc) and one was a household contact of a shipyard worker. The tremolite burdens for the asbestosis cases were one to two orders of magnitude greater than those for the mesothelioma cases. Our study confirms the relationship between tremolite exposure and the development of asbestos-associated diseases. Furthermore, the finding of relatively modest elevations of tremolite content in some of our mesothelioma cases suggests that, at least for some susceptible individuals, moderate exposures to tremolite-contaminated dust can produce malignant pleural mesothelioma.     

Routes of asbestos exposure and the development of mesothelioma in an English region.

OBJECTIVES: To investigate the contribution of exposure to asbestos through different routes in the development of mesothelioma. METHODS: Case-control study. 185 confirmed cases of mesothelioma and 160 controls were identified, when death had occurred between 1979 and 1991 in four health districts in Yorkshire. The surviving relatives were interviewed to ascertain lifetime exposure to asbestos. Adjusted odds ratios (ORs) of exposure to asbestos (through occupational, paraoccupational, and residential routes) were calculated for cases and were compared with controls. RESULTS: Likely or possible occupational exposure to asbestos was more common in cases than in controls (OR 5.6, 95% confidence interval (95% CI) 3.1 to 10.1). After excluding those with likely or possible occupational exposure, likely or possible paraoccupational exposure was more common in cases than controls (OR 5.8, 95% CI 1.8 to 19.2). Only six cases of mesothelioma were identified as being solely exposed to asbestos through their residence, compared with nine controls. The OR for residential exposure to asbestos varied between 1.5 and 6.6, depending on which potential industrial sources were included, but the 95% CIs were so wide that slightly reduced or greatly increased odds comparing cases with controls could not be excluded. CONCLUSION: Study results support previous evidence that occupational and paraoccupational exposure to asbestos is associated with developing mesothelioma. Despite a rigorous search, purely residential exposure seemed to account for only 3% of identified cases. No firm conclusion can be drawn about the risks from residential exposure alone, as many of the study subjects could also have been occupationally or paraoccupationally exposed to asbestos.     

Malignant mesothelioma and duration of asbestos exposure: Correlation with tissue mineral fibre content

Among 441 cases of malignant mesothelioma in the author's files, there were 324 for whom reliable information was available regarding the duration of exposure to asbestos. Included were 298 pleural and 26 peritoneal mesotheliomas. The mean duration of exposure to asbestos was 23 ± 14 years for all cases, and was not different for the pleural and peritoneal groups. Lung tissue was available for analysis of mineral fibre content in 94 cases. Linear regression analysis showed a significant correlation between duration of exposure and asbestos bodies per gramme of wet lung as determined by light microscopy, and between duration of exposure and total uncoated fibres (5 μm or greater in length) as well as commercial amphibole fibres per gramme as determined by scanning electron microscopy (P < 0.05). Individuals with direct exposures had on average higher asbestos contents than patients with indirect exposures. Furthermore, for each duration of exposure, shipyard workers had on average higher asbestos contents than non-shipyard workers (P < 0.05). Mesotheliomas are associated with a wide range of durations of exposure to asbestos and pulmonary asbestos burdens, and there is a rough correlation between duration of exposure and pulmonary commercial amphibole content.     

Non-malignant chest x ray changes in patients with mesothelioma in a large cohort of asbestos insulation workers.

To assess the prevalence of non-malignant chest x ray abnormalities in cases of mesothelioma 184 cases of mesothelioma (72 pleural and 112 peritoneal) which had occurred in a cohort of asbestos insulation workers followed up since 1967 were studied. Chest x ray films of satisfactory quality, on which the presence or absence of non-malignant radiological changes indicating interstitial pulmonary fibrosis or pleural fibrosis or both, could be assessed with a high degree of certainty were available. In some cases (20% for pleural mesothelioma, 11.6% for peritoneal mesothelioma) non-malignant radiological changes were not radiologically detectable. Parenchymal interstitial fibrosis (small irregular opacities) only was found in a proportion of cases (25.4% of pleural mesotheliomas, 12.5% of peritoneal mesotheliomas). Pleural fibrosis only was detected in 17% of cases of pleural mesothelioma and 27% of cases of peritoneal mesothelioma. Most patients had both parenchymal and pleural fibrosis. Although these results tend to indicate that in peritoneal mesothelioma the proportion of pleural fibrosis is significantly higher, these findings might have been due to the fact that in most cases of pleural mesothelioma non-malignant changes were interpreted in one hemithorax only. In 46 cases (21 pleural, 25 peritoneal) in which sufficient lung tissue was available histopathology of lung parenchyma indicated the presence of interstitial fibrosis; in 20 (43.5%) of these the chest x ray film had been read as negative. Thus the absence of radiologically detectable small opacities on the chest x ray film does not exclude the existence of interstitial pulmonary fibrosis in cases of mesothelioma among insulation workers. With lower levels of exposure (such as in family contacts of asbestos workers) it is conceivable that mesothelioma might occur in the absence of interstitial pulmonary fibrosis.     

Non-malignant chest x ray changes in patients with mesothelioma in a large cohort of asbestos insulation workers

To assess the prevalence of non-malignant chest x ray abnormalities in cases of mesothelioma 184 cases of mesothelioma (72 pleural and 112 peritoneal) which had occurred in a cohort of asbestos insulation workers followed up since 1967 were studied. Chest x ray films of satisfactory quality, on which the presence or absence of non-malignant radiological changes indicating interstitial pulmonary fibrosis or pleural fibrosis or both, could be assessed with a high degree of certainty were available. In some cases (20% for pleural mesothelioma, 11.6% for peritoneal mesothelioma) non-malignant radiological changes were not radiologically detectable. Parenchymal interstitial fibrosis (small irregular opacities) only was found in a proportion of cases (25.4% of pleural mesotheliomas, 12.5% of peritoneal mesotheliomas). Pleural fibrosis only was detected in 17% of cases of pleural mesothelioma and 27% of cases of peritoneal mesothelioma. Most patients had both parenchymal and pleural fibrosis. Although these results tend to indicate that in peritoneal mesothelioma the proportion of pleural fibrosis is significantly higher, these findings might have been due to the fact that in most cases of pleural mesothelioma non-malignant changes were interpreted in one hemithorax only. In 46 cases (21 pleural, 25 peritoneal) in which sufficient lung tissue was available histopathology of lung parenchyma indicated the presence of interstitial fibrosis; in 20 (43.5%) of these the chest x ray film had been read as negative. Thus the absence of radiologically detectable small opacities on the chest x ray film does not exclude the existence of interstitial pulmonary fibrosis in cases of mesothelioma among insulation workers. With lower levels of exposure (such as in family contacts of asbestos workers) it is conceivable that mesothelioma might occur in the absence of interstitial pulmonary fibrosis.     

Time trends and occupational risk factors for peritoneal mesothelioma in Sweden.

Epidemiologic data on peritoneal mesothelioma are scarce but exposure to asbestos is an identified risk factor. To characterize the disease, time trends, age-incidence relationships, and occupational risk factors for peritoneal mesothelioma were studied based on the Swedish Family-Database covering years 1961 to 1998. Peritoneal mesothelioma is a rare disease and only 96 male and 113 female cases were recorded during the 38-year period. Age-standardized incidence of the disease has increased for men until 1985 and leveled off thereafter. The incidence in women has been equally high but it has continued to increase toward the end of the follow-up period. The incidence was maximal at an age around 80 years for both genders. No female occupational or socioeconomic group was at risk. For men, 29% of the cases had typical asbestos related jobs with a SIR of 1.70. Bricklayers and plumbers had the highest risk of 7.22 and 5.12, respectively. Within limits of the sample size, no evidence was noted for risk from environmental exposures to asbestos because the risk of farmers and that of urban residents were not different.     

Malignant mesothelioma in Basse-Normandie, a French population study. Descriptive analysis, prognostic factors and survival

BACKGROUND: Malignant mesothelioma is a pleural and/or peritoneal tumor closely related to asbestos exposure, and its incidence should continue to increase during the first two decades of the 21(rst)century. The main prognostic factors described for this tumor are older age, sex, tumor stage and histological type. The aim of this study was to assess the incidence of pleural and peritoneal malignant mesothelioma in the County of Basse-Normandie (France), as well as their epidemiological characteristics, and the prognostic factors related to survival duration. METHODS: Cases were identified through repeated inquiries among all chest physicians and pathologists of the County of Basse-Normandie. A special care was taken in the validation of the diagnosis of each case. Incidence of mesothelioma was determined according to sex and age (5 years categories). Qualitative and quantitative variables were compared with the use of chi-square or Student's t tests respectively. Survival rate was calculated by Kaplan-Meier method, and prognostic factors were studied by means of Cox model. RESULTS: Study population consisted in all 80 malignant mesothelioma cases diagnosed in Basse-Normandie between the 1(rst) of September 1995 and the 31(rst) of August 1999. Annual incidence rates of pleural mesothelioma were 1.1/100 000 in men and 0.23/100 000 in women; annual incidence rates for peritoneal mesothelioma were 0.21/100 000 in men and 0.13/100 000 in women. Asbestos exposure was present in 63 cases (78.8%). The study of geographic distribution of mesothelioma cases revealed the influence of the main asbestos industrial settings, as well as the numerous scattered cases related to other occupational exposure. Mean survival duration was 9 months for pleural mesothelioma and 5 months for peritoneal mesothelioma. After adjustment on age, death risk was higher in asbestos-exposed than in non asbestos-exposed cases. CONCLUSION: This study confirms that malignant mesothelioma is closely related to asbestos exposure, but not only in main asbestos industrial settings. It suggests that asbestos exposure may take place among prognostic factors of this tumor.     

Malignant pleural mesothelioma in parts of Japan in relationship to asbestos exposure

Malignant pleural mesothelioma is induced by asbestos exposure. Many reports have described this situation in America and European countries, but a few have been published in Japan. In this study malignant pleural mesothelioma cases in hospitals located in an area facing the Seto Inland Sea were evaluated. A total of 106 patients were examined with 100 patients having had occupational exposure to asbestos and 6 patients without such histories of asbestos exposure. Ninety seven were male and 9 were female. Ages ranged from 41 to 87 yr with mean of 64.8+/-5.3 yr. Thirty seven cases showed epithelial type of tumor, 25 biphasic type and 15 showed sarcomatous. The remaining 23 cases had insufficient evidence for typing the tumor. The mean survival rate for all cases was 9.2+/-11.6 months. Fifty-one patients had occupational histories of shipyard work, 16 patients worked in asbestos cement piping, and the remainder were employed in miscellaneous jobs related asbestos exposure. The duration of asbestos exposure ranged up to 20 yr or longer with the mean of 17.2+/-8.9 yr and the average latent period for the occurrence of malignant pleural mesothelioma was more than 31 yr with the mean of 37.0+/-13.3 yr. Quantification of asbestos bodies in the lungs indicated a high concentration in most patients and the major types of asbestos fibers were crocidolite and amosite. Six cases appeared after exposure to chrysotile. These results indicated that ninety four percent of malignant pleural mesothelioma appeared due to the exposure to asbestos including crocidolite and amosite. The remainder may be blamed on exposure to chrysotile.