Mesothelioma and lung tumors attributable to asbestos among petroleum workers

Exposure to fibres and risk of pleural mesothelioma in the Norwegian Offshore Petroleum Workers cohort

OBJECTIVES

Pleural mesothelioma is a rare respiratory cancer, mainly caused by inhalation of asbestos fibres. Other inorganic fibres are also suggested risk factors. We aimed to investigate the association between exposure to asbestos or refractory ceramic fibres (RCFs) and pleural mesothelioma among male Norwegian offshore petroleum workers.

METHODS

Among 25 347 men in the Norwegian Offshore Petroleum Workers (NOPW) cohort (1965-1998), 43 pleural mesothelioma cases were identified through the Cancer Registry of Norway (1999-2022). A case-cohort study was conducted with 2095 randomly drawn non-cases from the cohort. Asbestos and RCF exposures were assessed with expert-made job-exposure matrices (JEMs). Weighted Cox regression was used to estimate HRs and 95% CIs, adjusted for age at baseline and pre-offshore employment with likely asbestos exposure.

RESULTS

An increased risk of pleural mesothelioma was indicated for the highest versus lowest tertile of average intensity of asbestos (HR=1.21, 95% CI: 0.57 to 2.54). Pre-offshore asbestos exposure (vs no such exposure) was associated with increased risk of pleural mesothelioma (HR=2.06, 95% CI: 1.11 to 3.81). For offshore workers with no pre-offshore asbestos exposure, an increased risk of pleural mesothelioma was found for the highest tertile of average intensity of asbestos (HR=4.13, 95% CI: 0.93 to 18), versus the lowest tertile. No associations were found between RCF and pleural mesothelioma.

CONCLUSIONS

Associations between JEM-based offshore asbestos exposure and pleural mesothelioma were confirmed in the NOPW cohort. Pleural mesothelioma risk was also associated with asbestos exposure before work in the offshore petroleum industry.

Cancer Incidence and Mortality among Petroleum Industry Workers and Residents Living in Oil Producing Communities: A Systematic Review and Meta-Analysis

Petroleum extraction and refining are major sources of various occupational exposures and of air pollution and may therefore contribute to the global cancer burden. This systematic review and meta-analysis is aimed at evaluating the cancer risk in petroleum-exposed workers and in residents living near petroleum facilities. Relevant studies were identified and retrieved through PubMed and Web of Science databases. Summary effect size (ES) and 95% confidence intervals (CI) were analysed using random effect models, and heterogeneity across studies was assessed (I2). Overall, petroleum industry work was associated with an increased risk of mesothelioma (ES = 2.09, CI: 1.58-2.76), skin melanoma (ES = 1.34, CI: 1.06-1.70 multiple myeloma (ES =1.81, CI: 1.28-2.55), and cancers of the prostate (ES = 1.13, Cl: 1.05-1.22) and urinary bladder (ES = 1.25, CI: 1.09-1.43) and a decreased risk of cancers of the esophagus, stomach, colon, rectum, and pancreas. Offshore petroleum work was associated with an increased risk of lung cancer (ES = 1.20; 95% CI: 1.03-1.39) and leukemia (ES = 1.47; 95% CI: 1.12-1.92) in stratified analysis. Residential proximity to petroleum facilities was associated with childhood leukemia (ES = 1.90, CI: 1.34-2.70). Very few studies examined specific exposures among petroleum industry workers or residents living in oil producing communities. The present review warrants further studies on specific exposure levels and pathways among petroleum-exposed workers and residents living near petroleum facilities.

Systematic Review and Meta-Analysis of Selected Cancers in Petroleum Refinery Workers

OBJECTIVE

We studied the risk of 11 cancers of a priori interest in petroleum refinery workers.

METHODS

Iterative searches identified 36 studies for the 11 cancer sites. Statistical heterogeneity and publication bias were assessed to enhance interpretation of meta-relative risks.

RESULTS

Statistical heterogeneity was marked for mesothelioma, but was largely due to study quality. Higher quality studies showed a meta-relative risk (RR) of 3.22, (95% prediction interval 1.45 to 7.23). Melanoma (meta-RR = 1.23) and acute lymphoid leukemia (meta-RR = 1.51), showed results consistent with higher risk, but both were driven by one or two studies. Eight other cancer outcomes showed summary meta-RR's consistent with unity.

CONCLUSIONS

Most cancer outcomes are consistent with background risk in refinery workers. This work has clarified an excess mesothelioma risk, conditional on study quality stratification. Continued surveillance is warranted for melanoma and ALL.

Mesothelioma Mortality Rates in Greece for the Period 2005-2015 Is Increased Compared to Previous Decades

Background and Objective: To present summary statistics regarding malignant mesothelioma (MM) mortality in Greece during the period 2005–2015 and compare it with previous decades, along with gender, age and geographical area analysis. Materials and Methods: The Hellenic Statistical Authority provided the data, which included all deaths for the period 1983 to 2015 that mentioned MM as the death cause in the corresponding death certificate. MM mortality rates have been calculated with respect to gender, age, and geographical location in Greece. Furthermore, a comparison analysis was made among three eleven consecutive year periods, in order to assess potential changes in the mortality rates. Results: The MM mortality rate has significantly increased during the period 2005–2015 both in males and females compared to earlier decades. The maximum number of MM deaths has shifted to an older age group of 70–80 years during the 2005–2015 period as compared to that of 1983–2004 in both genders. Additionally, MM mortality rates have significantly increased in all geographical areas except for the Epirus Prefecture. Conclusions: Our results demonstrate an increased MM mortality rate in Greece for the decade 2005–2015 as compared to the two previous decades. This increase is possibly due to the fact that the peak in asbestos production and use in Greece was in mid 1990s, while the asbestos ban came in effect in 2005. Based on these findings the MM epidemic in Greece has not yet peaked, therefore it is important to implement screening strategies for early MM detection.

Cancer risk in oil refinery workers: a pooled mortality study in Italy

Background:

Oil refinery workers are exposed to several well-established carcinogens and working in this type of industry has been classified by IARC as probable carcinogen to humans (Group 2A).

Objectives:

To examine the mortality experience of workers employed in four Italian oil refineries.

Methods:

The cohort included 5112 male workers ever employed between 1949 and 2011. The average follow-up period was 49 years. Standardized mortality ratios (SMR) and 95% Confidence Intervals (CI) were calculated using as reference age-gender-calendar specific regional rates. Analyses by duration of employment and latency were performed.

Results:

In the whole cohort, pleural cancer (6 deaths, SMR 1.59; 95% CI 0.71-3.53), brain cancer (14 deaths, SMR 1.47; 95% CI 0.87-2.49) and lymphatic leukemia (LL) (8 deaths, SMR 1.81; 95% CI 0.91-3.62) showed increased risks. All pleural cancers occurred after 10 years of latency and the highest risk was observed among workers with duration ≥20 years; the brain cancer excess was confined in the shortest duration and latency. The LL (and chronic lymphatic leukemia in particular) excess regarded workers with latency and duration longer than 20 years. Four deaths from acute myeloid leukemia (AML) were observed and all occurred after 20 years of latency (SMR 1.55, 95% CI 0.58-4.12); a two-fold-increased risk was observed in the longest duration. No increased risk for skin cancer has been observed in our study population.

Conclusion:

Our findings are consistent with recent evidence of an increased mortality from pleural and hematopoietic malignancies (AML and LL) among oil refinery workers. However, the lack of individual quantitative exposure data and the small number of observed events prevent the identification of the possible causal role of individual chemicals, including benzene, especially at the current very low exposure levels.

Epidemiological patterns of asbestos exposure and spatial clusters of incident cases of malignant mesothelioma from the Italian national registry

Background

Previous ecological spatial studies of malignant mesothelioma cases, mostly based on mortality data, lack reliable data on individual exposure to asbestos, thus failing to assess the contribution of different occupational and environmental sources in the determination of risk excess in specific areas. This study aims to identify territorial clusters of malignant mesothelioma through a Bayesian spatial analysis and to characterize them by the integrated use of asbestos exposure information retrieved from the Italian national mesothelioma registry (ReNaM).

Methods

In the period 1993 to 2008, 15,322 incident cases of all-site malignant mesothelioma were recorded and 11,852 occupational, residential and familial histories were obtained by individual interviews. Observed cases were assigned to the municipality of residence at the time of diagnosis and compared to those expected based on the age-specific rates of the respective geographical area. A spatial cluster analysis was performed for each area applying a Bayesian hierarchical model. Information about modalities and economic sectors of asbestos exposure was analyzed for each cluster.

Results

Thirty-two clusters of malignant mesothelioma were identified and characterized using the exposure data. Asbestos cement manufacturing industries and shipbuilding and repair facilities represented the main sources of asbestos exposure, but a major contribution to asbestos exposure was also provided by sectors with no direct use of asbestos, such as non-asbestos textile industries, metal engineering and construction. A high proportion of cases with environmental exposure was found in clusters where asbestos cement plants were located or a natural source of asbestos (or asbestos-like) fibers was identifiable. Differences in type and sources of exposure can also explain the varying percentage of cases occurring in women among clusters.

Conclusions

Our study demonstrates shared exposure patterns in territorial clusters of malignant mesothelioma due to single or multiple industrial sources, with major implications for public health policies, health surveillance, compensation procedures and site remediation programs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1301-2) contains supplementary material, which is available to authorized users.

Cancer incidence and mortality among temporary maintenance workers in a refinery/petrochemical complex in Korea

BACKGROUND

Petrochemical plant maintenance workers are exposed to various carcinogens such as benzene and metal fumes. In Korea, maintenance operations in petrochemical plants are typically performed by temporary employees hired as contract workers.

OBJECTIVES

The purpose of this retrospective study was to evaluate cancer risk in temporary maintenance workers in a refinery/petrochemical complex in Korea.

METHODS

Subjects consisted of 14 698 male workers registered in a regional petrochemical plant maintenance workers union during 2002-2007. Cancer mortality and incidence were identified by linking with the nationwide death and cancer registries during 2002-2007 and 2002-2005, respectively. Standardized mortality ratios (SMRs) and standardized incidence ratios (SIRs) were calculated for each cancer.

RESULTS

Increased SMR 3·61 (six cases, 95% CI: 1·32-7·87) and SIR 3·18 (five cases, 95% CI: 1·03-7·42) were observed in oral and pharyngeal cancers.

CONCLUSION

Our findings may suggest a potential association between oral and pharyngeal cancers and temporary maintenance jobs in the petrochemical industry. Future studies should include a longer follow-up period and a quantitative exposure assessment.

Asbestos-related Diseases in Italy: Epidemiologic Evidences and Public Health Issues

Epidemiologic information about asbestos-related diseases in Italy, derived from mortality data, epidemiologic surveillance, and analytical studies, is presented. These systems evidence exposures to asbestos and relative risks for populations exposed in work environments and also in the general environment, and provide objective data to identify sources of exposure and for risk management. Limitations and perspectives of Italian studies are considered, and public health issues evaluated: the risk for migrants, social security aspects, and asbestos-related disease in the courts. Although asbestos use was banned in 1992, information and risk communication efforts should be implemented to empower affected individuals and communities and to pursue equitable allocation of resources for primary prevention and health surveillance.

Pleural mesothelioma mortality and asbestos exposure mapping in Italy

BACKGROUND

An epidemic of asbestos-related diseases is ongoing worldwide. Mortality from malignant pleural neoplasms in Italy was analyzed, to estimate the health impact of asbestos at national and local level.

METHODS

Mortality from ICD-9 code 163 was considered, in the time-window 1995-2002, using National Bureau of Statistics data. National and regional standardized rates and municipal Standardized Mortality Ratios (SMR) were calculated. Municipal clusters were identified by applying Spatial Scan Statistics procedure. Relative risks (RR) express the ratio of risk within the cluster to the risk outside the cluster.

RESULTS

The national standardized annual mortality rate was 1.9 per 100,000. Significant clusters corresponded to asbestos-cement industries (Casale Monferrato: RR = 11.63), shipyards (Monfalcone, RR = 7.43), oil refineries (Falconara, RR = 2.52), petrochemical industries (Priolo, RR = 3.81).

CONCLUSIONS

The present study confirms malignant pleural neoplasms mortality as a suitable indicator of asbestos exposure at geographic level. In addition to asbestos-cement industries and shipyards, other industrial settings are associated with pleural neoplasm mortality.

Case-control study of pleural mesothelioma in workers with social security in Mexico

BACKGROUND

Environmental and occupational exposure to asbestos in Mexico in the past has been a cause of deaths and health damages. Its magnitude is unknown to date. Our objective was to identify the proportion of cases of malignant pleural mesothelioma (MPM) that can be attributed to and occupational exposure to asbestos.

METHODS

We carried out a case-control study of MPM in 472 workers insured by the Mexican Institute of Social Security, all Valley of Mexico residents, with 119 incident cases and 353 controls. Cases were histologically confirmed. Participants were questioned concerning their occupational history and sociodemographic data. Assignment to one of the four exposures was performed qualitatively by an expert hygienist. Odds ratios (ORs) and attributable risks (ARs) were calculated using a non-conditional logistic regression model.

RESULTS

A total of 80.6% of cases and 31.5% of controls had occupational exposure to asbestos. ORs were adjusted for age and gender and by exposure category, and exhibited an increase with probability of exposure as follows: 3.7(95% CI 1.3-10.4) for the likely category and 14.3(95% CI 8-26) for the certain category; AR in the group occupationally exposed to asbestos was 83.2%, and the population AR was 44%.

CONCLUSIONS

Our results show that the relationship between industrial uses of all forms of asbestos is generating an increase in mesothelioma-related diseases and deaths among Mexican workers. As a public health policy, Mexico should prohibit the use of asbestos in all production processes with the aim of controlling the epidemic and preventing the occurrence of new cases of MPM.

Comparison bias and dilution effect in occupational cohort studies

Health effects of occupational exposures are frequently evaluated by comparing the mortality of a whole cohort of workers with that of the general population. This study design may be affected by two major biases: a dilution effect (DE), due to the inclusion of unexposed subjects in the study cohort, and a comparison bias (CB), due to the different distribution of risk factors in the reference population. A theoretical model of the joint effect of DE and CB is proposed. Their impact was evaluated in two actual cohorts, selecting specific causes of death based on a priori hypotheses of an association. A linear relationship between the risk estimates and the two biases was found after applying either direct or indirect standardization to adjust for confounding. In the two cohorts, higher risks in exposed workers emerged only after adjusting for DE and CB. Cohort studies without an internal referent group may provide unreliable results.

Update of mortality and cancer incidence in the Australian petroleum industry cohort

OBJECTIVES

To update the analysis of the cohort mortality and cancer incidence study of employees in the Australian petroleum industry.

METHODS

Employees of Australian Institute of Petroleum member companies were enrolled in the cohort in four industry-wide surveys between 1981 and 1999. Mortality of 16,547 males and 1356 females was determined up to 31 December 2001 and cancer incidence to 31 December 2000. Cause specific mortality and cancer incidence were compared with those of the Australian population by means of standardised mortality ratios (SMRs) and standardised incidence ratios (SIRs). Associations between increased incidence of specific cancers and employment in the petroleum industry were tested by trends according to period of first employment, duration of employment, latency, and hydrocarbon exposure, adjusting for personal smoking history where appropriate.

RESULTS

There was a significant elevation of the incidence of mesothelioma (SIR 1.77, 95% CI 1.05 to 2.79), melanoma (SIR 1.37, 95% CI 1.19 to 1.58), and prostate cancer (SIR 1.18, 95% CI 1.04 to 1.34). The SIRs of all leukaemias and of acute non-lymphocytic leukaemia (ANLL) were not significantly different from unity, but all 11 ANLL cases were clustered in the middle to high hydrocarbon exposure categories. Tanker drivers had a significantly elevated incidence of kidney cancer (12 cases v 5.84 expected, SIR 2.05, 95% CI 1.06 to 3.59). Lung cancer incidence was significantly reduced (SIR 0.69, 95% CI 0.57 to 0.83)

CONCLUSIONS

Most cases of mesothelioma are probably related to past exposure to asbestos in refineries. No occupational cause has been identified for the excess of melanoma, or prostatic or bladder cancer. The possibility of a causal relationship between cancer of the kidney and hydrocarbon exposure warrants further study. It is uncertain whether benzene exposures, particularly past levels of exposure, have been high enough to cause ANLL.

Lung cancer and mesothelioma in towns with environmental exposure to asbestos in Eastern Anatolia

OBJECTIVE

Our previous study demonstrated the presence of environmental tremolite and chrysotile asbestos fiber exposure in Hekimhan town in Malatya located in eastern Turkey. The aim of this study was to investigate whether environmental asbestos exposure increases the incidence of lung cancer and mesothelioma.

METHOD

One hundred and forty-nine patients with mesothelioma and lung cancer living in the center or in the towns of Malatya were retrospectively analyzed. The Incidences of lung cancer and mesothelioma were calculated.

RESULTS

The incidences of lung cancer and mesothelioma were 3.39/100,000 and 0.21/100,000, respectively, for the whole population of Malatya; while they were 8.23/100,000 and 1.45/100,000 in Hekimhan. The incidences were strikingly high (22.39/100,000 for lung cancer and 7.46/100,000 for mesothelioma) in Arguvan, another town in Malatya where an analysis for asbestos could not be performed. The overall incidence in Turkey was reported as 5.9/100,000 by the Health Ministry in 1994. The incidences of lung cancer were nearly 1.3-fold higher in Hekimhan and fourfold higher in Arguvan then in the general population of Turkey.

CONCLUSION

The incidences of mesothelioma and lung carcinoma in Hekimhan were higher than those of the general population in Turkey, suggesting a role of environmental asbestos exposure in lung cancer and mesothelioma.

Asbestos Exposure and Cancer Mortality among Petroleum Refinery Workers: A Poisson Regression Analysis of Updated Data

The authors investigated the relationship between asbestos exposure and respiratory cancer mortality among maintenance workers and other blue-collar workers at an Italian oil refinery. The cohort contained 931 men, 29,511 person-years, and 489 deaths. Poisson regression analysis using white-collar workers as an internal referent group provided relative risk estimates (RRs) for main causes of death, adjusted for age, age at hiring, calendar period, length of exposure, and latency. Among maintenance workers, RRs for all tumors (RR = 1.50), digestive system cancers (RR = 1.41), lung cancers (RR = 1.53), and nonmalignant respiratory diseases (RR = 1.71) were significantly increased (p < 0.05); no significant excess was found for all causes and among maintenance (RR = 1.12) and other blue-collar workers (RR = 1.01). Results confirm the increased risk of death from respiratory diseases and cancer among maintenance workers exposed to asbestos, whereas other smoking-related diseases (circulatory system) were not statistically different among groups.

Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry

AIMS

To update the analysis of the cohort mortality and cancer incidence study of employees in the Australian petroleum industry.

METHODS

Employees from 1981 to 1996 were traced through the Australian National Death Index and the National Cancer Statistics Clearing House. Cause specific mortality and cancer incidence were compared with those of the Australian population by means of standardised mortality ratios (SMRs) and standardised incidence ratios (SIRs). Associations between increased incidence of specific cancers and employment in the petroleum industry were tested by trends according to period of first employment, duration of employment, latency, and hydrocarbon exposure, adjusting for personal smoking history where appropriate. Total follow up time was 176 598 person-years for males and 10 253 person-years for females.

RESULTS

A total of 692 of the 15 957 male subjects, and 16 of the 1206 female subjects had died by the cut off date, 31 December 1996. In males, the all-cause SMR and the SMRs for all major disease categories were significantly below unity. There was a non-significant increase of the all-cancer SIR (1.04, 95% CI 0.97 to 1.11). There was a significant increase of the incidence of melanoma (SIR 1.54, 95% CI 1.30 to 1.81), bladder cancer (SIR 1.37, 95% CI 1.00 to 1.83), and prostate cancer (SIR 1.19, 95% CI 1.00 to 1.40), and a marginally significant excess of pleural mesothelioma (SIR 1.80, 95% CI 0.90 to 3.22), leukaemia (SIR 1.39, 95%CI 0.91 to 2.02), and multiple myeloma (SIR 1.72, 95% CI 0.96 to 2.84).

CONCLUSIONS

Most cases of mesothelioma are probably related to past exposure to asbestos in refineries. The melanoma excess may be the result of early diagnosis. The excess bladder cancer has not been observed previously in this industry and is not readily explained. The divergence between cancer incidence and cancer mortality suggests that the "healthy worker effect" may be related to early reporting of curable cancers, leading to increased likelihood of cure and prolonged mean survival time.

Current controversies regarding the role of asbestos exposure in the causation of malignant mesothelioma: the need for an evidence-based approach to develop medicolegal guidelines

Asbestos is a group of fibrous silicate minerals that includes two mineralogic groups: amphiboles and serpentines. While the carcinogenic role of amphiboles (eg, crocidolite and amosite) is well established, medical "experts" that tend to strongly advocate their views currently argue in medicolegal cases multiple specific issues regarding the carcinogenicity of asbestos fibers. For example, it is controversial whether chrysotile causes malignant mesothelioma (MM); what are the specific carcinogenic thresholds for amphiboles and chrysotile; what occupations are truly at risk to develop MM as a result of asbestos exposure; what is the role of chrysotile in the development of peritoneal MM; how to assign causation in individuals exposed to multiple industrial products containing variable concentrations of various asbestos fibers; and, what criteria should be used to accept causation in household exposure cases and others. The causation criteria currently acceptable in U.S. courts are surprisingly flexible and subject to variable interpretation by medical "experts." At a time where thousands of individuals are claiming causation of MM by asbestos exposure, there is a need to develop more specific causation guidelines based on scientific evidence. Evidence-based medicine has been proposed as a new approach to the study, teaching, and the practice of medicine and has been used as a process of systematically reviewing the relevant studies in the literature to assess their scientific validity and development of guidelines. This article summarizes some of the current controversies regarding the role of asbestos exposure in the causation of MM and suggests the need for future evidence-based medicine-type studies to develop causation guidelines that could be used consistently during litigation.

Application of a method to evaluate the quality of work histories and document the exposure assessment process

BACKGROUND

Review of work history records by industrial hygienists is an important component of many occupational epidemiologic studies. A number of factors may influence the hygienist, such as the quality of the data and his or her previous experience. As part of a case-control study of mesothelioma, a system was developed to capture data on several factors that can be considered in a review of work history information.

METHODS

The overall quality of the work history record was described by noting the completeness and the consistency of the information; for any potential exposures, the reviewer experience on which the decision was based and the relative quality of the information were categorized. Because of the potential for mesothelioma cases and their next-of-kin to have undergone rigorous questioning about previous asbestos exposure an evaluation of the knowledge of the respondent was included. The frequency and intensity of exposure were also evaluated.

RESULTS

Evaluation of 3,444 work records is described. The importance of data completeness in the overall evaluation of quality is shown; follow-up questions regarding specific work tasks provide information not elicited in the standard interview process. The use of the literature was an important resource to the reviewer. Asbestos was reported by the respondent as an exposure on 149 work records; of these, 111 (74%) were judged to represent an unusual level of knowledge for a next-of-kin respondent.

CONCLUSIONS

The approach presented allows capture of information about data quality and experience of the reviewer in an epidemiologic analysis. The ratings of frequency and intensity of exposure allow exploration of differences in exposure-response analyses using various exposure metrics.

Asbestos fiber burdens in lung tissues of Hong Kong Chinese with and without lung cancer

To investigate the asbestos exposure level in non-occupational population and its relation to lung cancer, pulmonary asbestos fiber counts were observed with a modified alkali digestion method, in lung tissues from 65 random surgically treated lung cancer patients (42 males and 23 females) and that obtained from 107 random autopsy cases who died of either accidental death or acute myocardial infarction (44 males and 63 females) during 1987-1988. The patients and cases were all Hong Kong Chinese with no definite history of occupational exposure to asbestos. The non-lung cancer cases (NLCC) were divided into three groups based on different age ranges: 10 approximately, 40 approximately and 70 approximately years. The results showed that the medians of uncoated fiber counts (0, 32 and 52 fibers per mg dry tissue [f/mgDT] in the different age groups, respectively) increased in an age-dependent manner (P<0.01). However, the medians of coated fiber (asbestos body) counts were all 0 f/mgDT, with no statistically significant difference among the groups, showing a very low level of asbestos body burden in NLCC. In each age group, no difference in those counts between males and females was observed (P>0.05). Moreover, those counts in male lung cancer cases (medians of 62.5 and 17.5 f/mgDT, respectively) were greater than that in the control (32.5 and 0 f/mgDT, respectively) (P<0.01, P<0.05, respectively), however, regarding the female groups there was no statistically significant difference from the control. The results suggest that there is an environmental exposure to asbestos in Hong Kong Chinese, the level of which is, however, generally not sufficient to induce asbestos body. Environmental asbestos exposure in Hong Kong males may be one of the carcinogenic factors leading to lung cancer.