A prospective mortality study of 839 men employed in the manufacture of
asbestos cement products in 1969 examined
lung cancer risk in relation to lung
fibrosis seen on chest
x ray film, controlling for age, smoking, and exposure to
asbestos. Twenty or more years after hire, no excess of
lung cancer was found among workers without radiographically detectable lung
fibrosis, even among long term workers (greater than or equal to 21.5 years); nor was there a trend in risk by level of cumulative exposure to
asbestos among such workers. By contrast, employees with small opacities (greater than or equal to 1/0; ILO classification) experienced a significantly raised risk of
lung cancer (nine observed deaths v 2.1 expected), even though their exposures to
asbestos were similar to the exposures of long term workers without opacities. In this population, excess risk of
lung cancer was restricted to workers with
x ray film evidence of
asbestosis, a finding consistent with the view that
asbestos is a lung
carcinogen because of its fibrogenicity.