The results suggest that silicosis is a prerequisite for silica-related lung cancer. Risk of lung cancer did not vary with cumulative dust exposure if there was no silicosis. There was no correction for the effects of smoking. There was some evidence that silica dust/silicosis was not the only geological determinant of lung cancer risk.
Evidence from:
W Chen et al. Am. J. Ind. Med. (2006) Vol.49 p 67 – 76
“Exposures to Silica Mixed Dust and Cohort Mortality Study in Tin Mines: Exposure-Response Analysis and Risk Assessment of Lung Cancer”
In those with silicosis the risk of lung cancer varied with exposure; a clear rise in risk was detected once exposure to total dust exceeded 70 mgm-3 years. Respirable crystalline silica comprised around 4% of total dust in each mine.
Further detail: