A Cohort Study On Risk Factors Of Lung Cancer In Yunnan Tin Miners:Radon And Related Risk Factors

Lung cancer is the leading cause of cancer-related death in the world, with the incidence of and the mortality from the disease still on the increase in most areas. According to the third national retrospectively sampling survey results of the cause of malignant tumors’ death, Lung cancer is the top cause of malignant tumors’ deaths in China. Cigarette smoking is by far the most important risk factor for lung cancer, but other factors, such as environmental tobacco smoke, radon, occupational exposure can not be ignored.Since the1970s, we found both incidence and mortality of lung cancer among Yunnan tin miners(Hereinafter referred to Yunnan tin miners as "YTC miners") were high and had an remarkable occupational characteristic. From1992to1999, the collaborative project,"Early Marker Study of Lung Cancer Among Tin Miners in Yunnan, China" had been conducted by National Cancer Institute (NCI), Cancer Institute of Chinese Academy Medical Sciences (CICAMS) and Yunnan Tin corporation (YTC). The objective of our study is to investigate the epidemic of lung cancer in the high risk population who had received at least one screening examination among YTC, using the method of prospective cohort studies. The next object was to discuss the risk factors of lung cancer among Yunnan tin miners and the interactive effects of factors. The final objective was to provide some primary data for the prevention of lung cancer in special population who are at high risk of lung cancer in China.Study participants were from those participating in the project "early markers of lung cancer among Tin Miners in Yunnan, China"(Item Number:N01-CN-25420) established since1992. Inclusion criterias include:(1) current or retired workers at the age of40or older;(2) a history of10or more years of underground mining and/or smelting experience;(3) no cancer history;(4) informed consent. In this study, participants must have participated in the annual screening for lung cancer once or more from1992to1999.This data using in this study were collected from the above cohort established in1992and the followed lung cancer screening cohort (Item Number:263-MQ-511694). The data included the baseline information and results of annul screening conducted from1992to1999. We followed up the incidence of lung cancer and the miners’survival information and made a medical record abstraction of these lung cancer cases confirmed before the end of the year2001, the end time of our follow up. The working level month of cumulative radon exposure was calculation until the end of the year1995.The main results of our study are as follows:1. From1992to1999, there were9295miners who had participated in the annual screening for lung cancer. By the end of2001,502lung cancer cases were diagnosed, and the diagnosis time of34cases were not known. The average age of onset were66.81years. And of them443cases died.7449miners were exposed to radon for some time, with the average age of23.31years, and25%of them were exposed more than30years.2. There is no decline tendency of incidence during the follow up period. We do the Cochran-Armitage trend test, using the software SAS9.2, and get the result that Z=1.6375, P>0.05, no linear trend between standardized incidence and lung cancer with time pass by. The average incidence age of these followed ten years had extended to66.81compared42.50in the1950’.3. After controlling the known or potential confounders, multivariate Cox regression analysis shows the results that age, smoke, occupational exposure of radon and arsenic, and previous chronic bronchitis are independent risk factors of lung cancer among YTC miners, while education is a protective factor.4. The multivariate Cox regression analysis of relationship between lung cancer risk and age at first radon exposure, rate of radon exposure among radon-exposed miners shows that (1) treat "age at first radon exposure" and "rate of radon exposure" as categorical variables, there is no significant correlation;(2) treat "age at first radon exposure" and "rate of radon exposure" as continuous variables, rate of radon exposure is a protective factor of lung cancer and adjusted hazard ratio (HR)=0.98(95%CI:0.96-0.99).5. There is additive interaction between cumulative radon exposure and tobacco use on the death of lung cancer. RERI=0.92(0.11-1.73), AP=0.25(-0.05-0.55), S=(0.85-2.70). No significant multiplicative interaction are found.6. Among radon exposed Yunnan tin miners:radon exposure is more dangerous than tobacco use on lung cancer; radon exposure increases lung cancer mortality without smoking, while tobacco use alone can’t increase lung cancer mortality rate; after controlling smoking, lung cancer mortality vary positively with cumulative radon exposure, which is the same with smoking after controlling radon exposure.International and domestic studies show that multiple risk factors are associated with lung cancer among miners. Committee on Health Effects of Exposure to Radon gave the systematic research results in1999. This study was based on the latest calculating method of cumulative radon exposure. Made detailed study on tobacco use and radon exposure, made intensive and systematic research on potential risk factors of Yunnan tin miners, and made a deep discussion about age at first radon exposure and rate of radon exposure. In summary, this study provide a scientific basis for the prevention and control of occupational lung cancer.