Crystalline silica and lung cancer: a review of recent experimental evidence.

The International Agency for Research in Cancer (IARC) has recently stated that crystalline silica should be regarded as a potential carcinogen. The IARC bases this statement on a finding that there is limited evidence of carcinogenicity in humans and sufficient evidence for carcinogenicity in animals. Recent laboratory animal experiments demonstrating a carcinogenic response to silica exposure have intensified scientific and regulatory concern for crystalline silica as a respiratory carcinogen. Studies of human populations have been contradictory in demonstrating a causal relationship between crystalline silica exposure and lung cancer. This paper reviews recent experimental evidence and attempts to identify the gaps and inconsistencies in our understanding of the relationship between exposure to crystalline silica and the two diseases of concern: silicosis and pulmonary neoplasia. Given our current level of understanding and the need for more scientific data it seems premature to initiate changes in exposure regulations at this time.