Study of occupational lung cancer in asbestos factories in China

Current Asbestos Exposure and Future Need for Palliative Care in India

Asbestos-related diseases (ARDs) are incurable but entirely preventable. Due to India's continuing use of asbestos, ARD patients will increase to a high number in the next three to four decades. This will increase the burden on palliative care system which is in nascent stage presently. Palliative care is the mainstay of the management of ARDs. Unfortunately, the burden on palliative care is likely to increase due to multiple factors contributed by India's demographic and economic changes. In the near future, there will be at least 12.5 million ARD patients and 1.25 million asbestos-related cancer patients worldwide, and half of these will be in India. It is high time to introspect about our ability to engage with this future problem. The paper also discusses the organization of this future problem of ARDs and possible action points toward future access to palliative care for ARD patients.

Stomach cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies

Background:

A recent Monographs Working Group of the International Agency for Research on Cancer concluded that there is limited evidence for a causal association between exposure to asbestos and stomach cancer.

Methods:

We performed a meta-analysis to quantitatively evaluate this association. Random effects models were used to summarise the relative risks across studies. Sources of heterogeneity were explored through subgroup analyses and meta-regression.

Results:

We identified 40 mortality cohort studies from 37 separate papers, and cancer incidence data were extracted for 15 separate cohorts from 14 papers. The overall meta-SMR for stomach cancer for total cohort was 1.15 (95% confidence interval 1.03–1.27), with heterogeneous results across studies. Statistically significant excesses were observed in North America and Australia but not in Europe, and for generic asbestos workers and insulators. Meta-SMRs were larger for cohorts reporting a SMR for lung cancer above 2 and cohort sizes below 1000.

Conclusions:

Our results support the conclusion by IARC that exposure to asbestos is associated with a moderate increased risk of stomach cancer.

Cancer mortality in Chinese chrysotile asbestos miners: exposure-response relationships

Objective

This study was conducted to assess the relationship of mortality from lung cancer and other selected causes to asbestos exposure levels.

Methods

A cohort of 1539 male workers from a chrysotile mine in China was followed for 26 years. Data on vital status, occupation and smoking were collected from the mine records and individual contacts. Causes and dates of death were further verified from the local death registry. Individual cumulative fibre exposures (f-yr/ml) were estimated based on converted dust measurements and working years at specific workshops. Standardized mortality ratios (SMRs) for lung cancer, gastrointestinal (GI) cancer, all cancers and nonmalignant respiratory diseases (NMRD) stratified by employment years, estimated cumulative fibre exposures, and smoking, were calculated. Poisson models were fitted to determine exposure-response relationships between estimated fibre exposures and cause-specific mortality, adjusting for age and smoking.

Results

SMRs for lung cancer increased with employment years at entry to the study, by 3.5-fold in ≥10 years and 5.3-fold in ≥20 years compared with <10 years. A similar trend was seen for NMRD. Smokers had greater mortality from all causes than nonsmokers, but the latter also had slightly increased SMR for lung cancer. No excess lung cancer mortality was observed in cumulative exposures of <20 f-yrs/ml. However, significantly increased mortality was observed in smokers at the levels of ≥20 f-yrs/ml and above, and in nonsmokers at ≥100 f-yrs/ml and above. A similarly clear gradient was also displayed for NMRD. The exposure-response relationships with lung cancer and NMRD persisted in multivariate analysis. Moreover, a clear gradient was shown in GI cancer mortality when age and smoking were adjusted for.

Conclusion

There were clear exposure-response relationships in this cohort, which imply a causal link between chrysotile asbestos exposure and lung cancer and nonmalignant respiratory diseases, and possibly to gastrointestinal cancer, at least for smokers.

Respiratory medicine in China: progress, challenges, and opportunities

The past century witnessed a rapid development of respiratory medicine in China. The major burden of respiratory disease has shifted from infectious diseases to chronic noninfectious diseases. Great achievements have been made in improving the national standard of clinical management of various respiratory diseases and in smoking control. The specialty of respiratory medicine is expanding into pulmonary and critical care medicine. Nevertheless, respiratory diseases remain a major public health problem, with new challenges such as air pollution and nosocomial infections. This review describes the history, accomplishments, new challenges, and opportunities in respiratory medicine in China.

Cause-specific mortality in a Chinese chrysotile textile worker cohort

Chrysotile asbestos has continued to be mined and used in China, but its health effects on exposed workers have not been well documented. This study was conducted to give a complete picture about cause-specific mortality in Chinese asbestos workers. A cohort of 586 males and 279 females from a chrysotile textile factory were prospectively followed for 37 years. Their vital status was identified, and the date and underlying cause of death were verified from death registry. Cause-specific standardized mortality ratios by gender were computed with nationwide gender- and cause-specific mortality rates as reference. Male workers were 11 years older, and had 6 years longer exposure duration than females; 79% in males and 1% in females smoked. In males, the mortality rate of all cancers doubled; both larynx and lung cancer were four-fold, and mesothelioma was 33-fold. In females, there was slightly excess mortality from lung cancer and all cancers, and significant increase in mesothelioma and ovarian cancer. Other significantly increased mortality was seen from cancers of thymus, small intestine and penis in males, and cancers of bone and bladder in females. In addition to asbestosis, mortality from pulmonary heart disease was significantly elevated in both genders. The data confirmed significantly excess mortality from mesothelioma in either gender, lung and larynx cancers in males, and ovarian cancer in females. A gender difference in mortality from lung cancer and all cancers could be mainly due to the discrepancies in age, exposure duration and smoking between the male and female workers.

Occupational exposure to asbestos and ovarian cancer: a meta-analysis

OBJECTIVE

A recent Monographs Working Group of the International Agency for Research on Cancer (IARC) concluded that there is sufficient evidence for a causal association between exposure to asbestos and ovarian cancer. We performed a meta-analysis to quantitatively evaluate this association.

DATA SOURCES

Searches of PubMed and unpublished data yielded a total of 18 cohort studies of women occupationally exposed to asbestos.

DATA EXTRACTION

Two authors independently abstracted data; any disagreement was resolved by consulting a third reviewer.

DATA SYNTHESIS

All but one study reported standardized mortality ratios (SMRs) comparing observed numbers of deaths with expected numbers for the general population; the exception was a study that reported standardized incidence ratios. For simplicity, we refer to all effect estimates as SMRs. The overall pooled SMR estimate for ovarian cancer was 1.77 (95% confidence interval, 1.37-2.28), with a moderate degree of heterogeneity among the studies (I2 = 35.3%, p = 0.061). Effect estimates were stronger for cohorts compensated for asbestosis, cohorts with estimated lung cancer SMRs > 2.0, and studies conducted in Europe compared with other geographic regions. Effect estimates were similar for studies with and without pathologic confirmation, and we found no evidence of publication bias (Egger's test p-value = 0.162).

CONCLUSIONS

Our study supports the IARC conclusion that exposure to asbestos is associated with increased risk of ovarian cancer.

Mortality in a Chinese chrysotile miner cohort

BACKGROUND

Few data were available to address cause-specific mortality in asbestos miners in China. This study observed a cohort of workers from the largest chrysotile asbestos mine to evaluate the association between asbestos exposure and cause-specific mortality.

METHODS

The cohort consisting of 1,539 male workers was observed from 1981 to 2006. Information on occupational and smoking history and vital status was obtained through personnel records and individual contact. Causes and dates of deaths were verified from hospitals. Workers were divided into two groups: miners and millers (miner group) and control group (not direct exposed). Recent asbestos dust measurements in the workplaces showed that the concentrations ranged from 12 to 197 mg/m(3). Amphibole contamination was very low. Cox proportional hazard models with competing risks were fit to estimate hazard ratios for cause-specific mortality associated with asbestos exposure (miners vs. controls). In addition, standardized mortality ratios (SMRs) were calculated based on national mortality rates.

RESULTS

All mortality rates of selected causes, particularly lung cancer, were substantially higher in the miner group than in the controls. SMRs of lung cancer and nonmalignant respiratory diseases in the miners were 4.71 (95% CI, 3.57, 6.21) and 3.53 (2.78, 4.48), respectively. The controls had similar mortality rates of all causes, lung cancer, all cancers as national rates, but a higher mortality from respiratory diseases. Asbestos exposure was related to a 4.6-fold mortality risk for lung cancer and over threefold risk for all cancers and respiratory diseases, while smoking and age were adjusted. The highest SMR of lung cancer was observed in miners who smoked.

CONCLUSION

The results suggested excessive cause-specific mortality, in particular from lung cancer and respiratory diseases, in the cohort, which was associated with exposure to chrysotile asbestos.

Relation between exposure to asbestos and smoking jointly and the risk of lung cancer

OBJECTIVES

To review evidence about the joint relation of exposure to asbestos and smoking on the risk of lung cancer to answer three questions: (1) does asbestos increase risk in non-smokers; (2) are the data consistent with an additive model; and (3) are the data consistent with a multiplicative model?

METHODS

Analysis of 23 studies reporting epidemiological evidence on the joint relation. Comparison of risk of lung cancer in subjects unexposed to asbestos or smoking, exposed to asbestos only, to smoking only, or to both. Estimation of the relative risk associated with asbestos exposure in non-smokers and of statistics testing for additivity and multiplicativity of risk.

RESULTS

Eight of the 23 studies provided insufficient data on the risk of lung cancer in non-smokers to test for possible effects of asbestos. Asbestos exposure was associated with a significantly (p<0.05) increased risk in non-smokers in six of the remaining studies and with a moderately increased, but not significant, increase in a further six. In two of the three studies that found no increase, asbestos exposure was insufficient to increase risks in smokers. In 30 of 31 data sets analysed, risk in the combined exposure group was greater than predicted by the additive model. There was no overall departure from the multiplicative model, the proportional increase in risk of lung cancer with exposure to asbestos being estimated as 0.90 (95% confidence interval (95% CI) 0.67 to 1.20) times higher in smokers than non-smokers. For two studies significant (p<0.05) departures from a multiplicative relation were found in some, but not all, analyses. Reasons are presented why these may not indicate true model discrepancies.

CONCLUSIONS

Asbestos exposure multiplies risk of lung cancer by a similar factor in non-smokers and smokers. The extent to which it multiplies risk varies between studies, no doubt depending on the type of asbestos involved, and the nature, extent, and duration of exposure.

Occupational exposure to chrysotile asbestos and cancer risk: a review of the amphibole hypothesis

OBJECTIVES

This article examines the credibility and policy implications of the "amphibole hypothesis," which postulates that (1) the mesotheliomas observed among workers exposed to chrysotile asbestos may be explained by confounding exposures to amphiboles, and (2) chrysotile may have lower carcinogenic potency than amphiboles.

METHODS

A critical review was conducted of the lung burden, epidemiologic, toxicologic, and mechanistic studies that provide the basis for the amphibole hypothesis.

RESULTS

Mechanistic and lung burden studies do not provide convincing evidence for the amphibole hypothesis. Toxicologic and epidemiologic studies provide strong evidence that chrysotile is associated with an increased risk of lung cancer and mesothelioma. Chrysotile may be less potent than some amphiboles for inducing mesotheliomas, but there is little evidence to indicate lower lung cancer risk.

CONCLUSIONS

Given the evidence of a significant lung cancer risk, the lack of conclusive evidence for the amphibole hypothesis, and the fact that workers are generally exposed to a mixture of fibers, we conclude that it is prudent to treat chrysotile with virtually the same level of concern as the amphibole forms of asbestos.