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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 5. Respiratory Malignancies

5.3 Silica-Induced Lung Cancer

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Issue

RDRP has worked to obtain better information on whether inhaled silica is a lung carcinogen and, if so, how the risk of lung cancer varies with intensity or extent of dust exposure. The issue dates back to the early 1980s, when the hypothesis that exposure to airborne silica dust could cause lung cancer was first posed along with supporting evidence. Because silica exposure is ubiquitous and prevalent throughout a wide range of industries and occupations, many millions of workers are exposed daily. Therefore, even if a silica-attributable risk of developing lung cancer were small, the large group of exposed workers made the issue highly important. Further evidence was needed because the existing information was somewhat equivocal and also subject to a number of limitations, one of which was a general absence of measured dust exposures.

Approach

To provide further evidence on this important issue, RDRP researchers conducted two epidemiologic studies centered on assessing the mortality experience of cohorts of silica-exposed workers for which personal dust exposures could be derived. These have involved a cohort of gold miners and a cohort of granite workers. Using standard epidemiologic methods, these cohorts were analyzed for excess lung cancer mortality and also for trends of increasing risk with increasing dust exposure. For previous RDRP studies of lung cancer in silica-exposed cohorts, there were no exposure estimates and so the results were less conclusive.

Output and Transfer

RDRP scientists have published results from the two main epidemiologic studies, both of which have been influential in the risk assessment arena. The principal report describes a study of gold miners (10, A5-23, two other reports are focused on Vermont granite workers (11, 12, A5-24 A5-25).

 Intermediate Outcomes

These two RDRP studies have been influential in the on-going debate on the carcinogenicity of silica dust. They were among the 10 most-influential studies in the IARC evaluation of silica dust in 1997.149 In that evaluation, IARC concluded that there was sufficient evidence from human studies of the carcinogenicity of inhaled crystalline silica to designate crystalline silica as a Group I carcinogen (in the IARC chapter on silica more than 10 percent of the reference materials were authored or co-authored by RDRP scientists).149 These studies were recently featured and discussed in an international workshop organized by a European industry group in 2005.

What’s Ahead

 Studies of silica-associated oxidative DNA damage, gene activation, and carcinogenesis in a p53 deficient mouse model are on-going (see chapter 3.2d).

149. IARC Monographs [1997]. Silica, Some Silicates, Coal Dust and Para-Aramid Fibrils. 68:41-242.