Study Objectives and Design

Strengths and Limitations

  • Location: this is the mine that produces approximately 20% of the world′s chrysotile today.

  • Size: at any given time point, between 6000 and 10 000 workers were employed. The total size of the cohort is expected to exceed 30 000 workers.

  • Inclusion of women: at least one fifth (> 6000) of the workforce is female. Women were employed in most areas of the processing mills and were therefore exposed at a full range of exposures. This will enable the investigation of female-specific cancers, although the absolute numbers of cancer deaths for most individual sites will be limited. A recognized limitation of this study is the limited availability of smoking data, but exploration of sex differences in cancer risks can serve as a surrogate for differences by smoking status, given that smoking prevalence is much lower in women.

  • Long follow-up period: the cancers that arise from exposure to asbestos typically occur 30 or more years after first exposure. The study will include workers who will have been followed up for as many as 50 or more years after first employment with the company (e.g. a worker employed 1950-1980 could be followed up to 2010, 60 years after first exposure).

  • Detailed data on dust concentrations: more than 90 000 dust concentration measurements are available across the mine and mills for the period 1950-2001, for estimating exposures. There are also more than 1000 parallel gravimetric dust and asbestos fibre count concentrations measured at multiple time points (1995, 2007, 2013-2014) in the mine and two of the factories, which will be used to estimate exposure to asbestos fibres for the whole observation period.