Nested Case-control Study Of Lung Cancer In Copper Mine And Iron Mine

Lung cancer is the highest mortality and morbidity of malignant tumor in the world. Especially in recent years, women lung cancer has been increased gradually. In past 20 years, the incidence of lung cancer increased by 10% annually in China. Since the beginning of 21st century, lung cancer has been the first cause of death in China, the mortality of lung cancer rose from the top four in 1970s to the first. The number of new lung cancer has reached as many as 210,000 people in China each year, including non-small cell carcinoma accounts for 70-80%. It can be predicted that the influencing factors of lung cancer are becoming more diverse and serious. With acceleration of industrialization and urbanization, lung cancer has become a serious public health problem all over the world.The aim of this study was to investigate the risk factors of lung cancer and analyze interaction among them. and to evaluate the effect of dust control techniques on the mortality of lung cancer. On the basis of previous cohort study, the 11016 copper and iron miners employed during 1960 to 1974 and at least 1 year from Hubei province, were extended followed up to the end of 2004. The study included 3 sections: section1, Evaluation of occupational hazards at the workplace of copper and iron mines; section 2, A nested case-control study of lung cancer in copper and iron miners ; section 3, A study of interactive analysis on lung cancer risk factors. SectionⅠEvaluation of occupational hazards in the workplace of copper mine and iron mineThe objective of this section was to evaluate the occupational hazards at the workplace in copper and iron mines by collecting historical data and records of occupational hazards. and to provide useful information for the health surveillance as well as protective policy-making in these mines and other related corporations.The monitoring of occupational hazards in Hubei copper and iron mines was initiated in 1950s. The historical data of dust monitoring during 1952～2004 was abstracted from the records of copper and iron mines determined by local industrial hygienists. For no record of dust exposure before 1952, the dust concentrations were estimated by specialists, industrial hygienists and experienced workers, mainly according to the current conditions of the workplace and dust control. Occupational hazards including total dust, respiratory dust, 30 chemistry elements, radon,γ-radiation and 17 polycyclic aromatic hydrocarbons (PAHs) were determined by specialists in Tongji Medical College in 1989 and 2007. The results were used to compare with monitor data by local industrial hygienists.The results showed that the total dust concentrations were very high in 1950s, with an average concentration of 11.00 mg/m3. However, the concentrations decreased sharply at the end of 1950s because wet suppression and other dust control techniques were installed and used. The concentration of dust ranged from 5.0 to 7.0mg/m3 during 1960s, it ranged from 2.5 to 7.5mg/m3 during 1970s and 1.7 to 2.7mg/m3 during 1980s, dust concentration changed from 1.5 to 2.5mg/m3 between 1990s and the end of follow-up. For the decentralization degree of copper and iron mine dust, the particles with aerodynamic diameter less than 5μm accounted for about 80.48%. The free silica content was about 27.5% in total dust and 9.7% in respiratory dust. The total dust concentrations of job titles under ground were higher than that on the ground. And the dust concentrations of blasting, drilling, crushing and packing were relatively high. The result of elements amount of dust samples were that the aluminum content in air and bulk dust was as high as 5033.3μg/g in copper mine and 11166.7μg/g in iron mine. The iron content in dust reached to 137666.7μg/g in copper mine and 11166.7μg/g in iron mine.The whole PAHs concentration was as high as 22.58μg/m3. Most of them in copper and iron mine were no carcinogenic PAHs. Radon andγ-radiation are not very high in copper and iron mines.SectionⅡA nested case-control study of lung cancer in copper mine and iron minerThe aim of this section was to explore the relationship between metal mine dust and primary lung cancer, and to evaluate the effects of smoking and other potential occupational factors on risk of lung cancer by a nested case-control study.A nested case-control study of 215 male lung cancer cases and 860 controls was initiated from a cohort study of 11016 subjects employed at least 1 year between 1972 and 1974 in copper and iron mines. One lung cancer case was matched to about 4 controls, based on age (decade of birth), sex, and mine. Controls that died at an age younger than the age at diagnosis of lung cancer of corresponding cases were excluded from analysis.The results indicated that the cumulative dust exposure, smoking, silicosis and history of TB were the possible risk factors of lung cancer, after adjusting for smoking. Comparing to dust-free group, the relative risk of lung cancer increased when cumulative exposures to total dust become higher. The positive dose-response relationship was observed between cumulative dust exposure and lung cancer. Smoking was significantly associated with risk of lung cancer; the relative risk of medial smoking group(OR=4.16) and low smoking group(OR=2.40) were higher than the non-smoking group. The risk suffering from lung caner of workers with silicosis was 1.42 times high as comparison with non-silicosis. The results could confirm the effect of silicosis on lung cancer because silicosis means high cumulative dust exposure. The later also caused high risk of lung cancer. And, comparing to worker without TB, the relative risk of history of TB was 3.42 (95%CI:1.54~7.87). The multivariate unconditional Logistic regression was performed to screen the risk factors of lung cancer. The main risk factors for lung cancer were smoking, dust exposure and history of TB.SectionⅢA study of interaction among lung cancer risk factorsThe result from part II showed that the high risk factors of lung cancer in copper and iron mines were cigarette smoking,dust exposure and history of TB. Their ORs were 3.7, 1.66 and 3.42. Here, we calculated RRs through putting interaction term into logistic regression model, to evaluate the interaction on lung cancer risk factors by the three measures of biological interaction(RERI, AP and S) presented by Rothman.The lung cancer and matched controls in part II were used in the analysis. This study indicated that dust exposure had not an additive model synergism on cigarette smoking. The relative excess risk due to interactions (RERI) was 1.93. the attributable proportion due to interaction (AP) was 33 % and the synergy index(S) was 1.67. History of TB also had not an additive model synergism on cigarette smoking. The relative excess risk due to interactions (RERI) was 9.13, the attributable proportion due to interaction (AP) was 59% and the synergy index (S) was 2.74.ConclusionIn this study, the possible occupational hazards in workplaces of two iron and copper mines were analyzed according to the results of long term monitoring. And a nested case-control study was conducted to evaluate potential risk factors of lung cancer in copper and iron mines. The three measures of biological interaction (RERI, AP and S) presented by Rothman were evaluated the interaction on lung cancer risk factors. The conclusions and findings were as follows:1. The average total dust concentration at the workplaces of copper and iron mines was as high as 11.00 mg/m~3 at the beginning of 1950s. The concentration ranged from 5.0 to 7.0mg/m~3 during 1960s, it ranged from 2.5 to 7.5mg/m~3 during 1970s and 1.7 to 2.7mg/m~3 during 1980s, dust concentration changed from 1.5 to 2.5mg/m~3 between 1990s and the end of follow-up. It shows that the total dust concentrations began decreasing, especially at the end of 1950s. which was attributed to wet suppression and other dust control techniques were installed and used. At the same time, other occupational hazards in copper and iron mines are complex. Among them, the concentrations of PAHs and radon were up to 22.58μg/m~3 and 0.07WL respectively at many worksites.2. The results showed that smoking , dust exposure and history of TB were main risk factors of lung cancer in copper and iron miners. The positive pose-response trend was shown between cumulative dust exposure and risk for lung cancer. And this study can not support that silicosis was risk factor of lung cancer.3. Dust exposure had not an additive model synergism on cigarette smoking. and History of TB also had not an additive model synergism on cigarette smoking.