Background
Chrysotile asbestos is the only type of asbestos produced and consumed in the world today. Although it has been established as a carcinogenic hazard, more precise quantification of the magnitude, dose–response relationship and timing of the cancer-specific risks of chrysotile is still needed.
 
Objectives
In 2009 Russian Ministry of Health invited IARC to study cancer risk in employees at one of the world’s largest operating chrysotile producers in Asbest, Sverdlovsk Region, Russia, that has been realized in a collaboration between IARC and IRIOH. Main objective was to investigate cancer mortality in workers exposed to chrysotile, especially to obtain more precise quantification of the site-specific cancer risks.
 
Methods
Study included all workers employed for at least 1 year between 1975 and 2010 and follow-up until the end of 2015. Cumulative exposure to dust was estimated based on workers’ complete occupational history linked to over 50 years systematically collected dust measurements. Exposure to chrysotile fibers was estimated using dust-to-fiber conversion factors. Smoking habits among living workers was evaluated. Relative risks and 95% confidence intervals were estimated. The cause-specific mortality in workers was compared with that of the general population of Sverdlovsk region where the mine and factories are located. Mortality in Asbest city was compared to the remaining Sverdlovsk region.
 
Results
 A total of 30445 (32% women) workers accumulated 721312 person-years at risk and 11110 (36%) died. Of the workers, 54% had more than 30 years since their first exposure. Clear exposure-response between cumulative dust and lung cancer mortality in men was observed, as well as a modest increase in the highest category of fiber exposure in women. Mesothelioma mortality (13 deaths) was increased also in highest exposure groups. For colorectal and stomach cancer, there were inconsistent associations. No associations were seen for laryngeal or ovarian cancer. In comparison with Sverdlovsk region overall mortality of men in the cohort was reduced by 14%, mainly because of the circulatory diseases; effect was weaker in women. Elevated mortality was observed for both sexes from diseases of the digestive system and blood and blood forming organs. Lung cancer mortality in men was increased among workers with highest cumulative exposure, while the increase in high exposed women was not reaching statistical significance. No increased SMRs were seen for laryngeal, stomach or ovarian cancers. Mortality rates overall in Asbest and the Sverdlovsk region were similar. Higher rates of cancer mortality and digestive diseases in Asbest and lower rates of unknown/ill-defined and circulatory disease in Asbest were observed. Mortality from oesophageal, urinary tract and lung cancers was higher for men and from stomach, colon, lung and breast cancers for women.
 
Conclusions/Implications.
One of the largest of its kind, the study notably included large number of female workers (32%). A unique individual reconstruction of cumulative exposures to dust and fibres; a multi-stage procedure for collecting hygienic and demographic data, verifying their quality with for instance using multiple sources of information when available, ensured the highest possible study quality in comparison with similar studies.