Shape of the exposure response relation for crystalline silica and risk of lung cancer
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Crystalline silica exposure mostly occurs in occupational settings such as mining, construction, several industries (e.g. foundries) and agriculture. Occupational exposure to silica dust is known to be related to several non-malignant respiratory health effects. In addition respirable crystalline silica has been classified as malignant by the International Agency for Research on Cancer (IARC) since 1997. However, conflicting data has fueled a debate against this classification for the past decade. In the presented study quantitative data on the exposure response relationship between occupational crystalline silica exposure and risk of lung cancer was evaluated by applying a formal meta regression. Data was collected from studies used in a meta-analysis performed by Lacasse and co-workers in 2009 and more recent studies which reported quantitatively on the relation between crystalline silica and lung cancer. The main aim was to shed light on the actual shape of the exposure response relation for respirable crystalline silica and lung cancer. Both a linear and a natural spline model were fitted to the data. The natural spline model fitted the data better and showed a small, but statistically significant (p =0.04) increase in lung cancer risk resulting from increasing crystalline silica exposure. This increase however was only observed at relatively low levels of cumulative exposure to crystalline silica.