In a recently published study, genetically modified mice did not develop lung tumors following exposure to styrene or styrene oxide. Based on these and other data, ACMA’s Government Affairs Committee advocates that styrene should not be considered a human carcinogen, and should be removed from the Report on Carcinogens.

An earlier finding that laboratory mice develop lung tumors following styrene exposure suggested the possible carcinogenicity of this substance in humans, possibly through the action of styrene metabolize styrene oxide. The recent study, however, strongly supports a mouse lung tumor mode-of-action (biological metabolic mechanism responsible for the tumors) that is not likely to occur in humans. To prepare transgenic mice for the study, researchers used a Nobel Prize winning technique to replace the mouse form of the primary styrene metabolizing enzyme with the human version.

Rats, which metabolize styrene more like humans than mice, do not develop any tumors even following high styrene exposure. A large cohort of highly-exposed composites industry workers, followed for several decades, does not have any styrene-exposure-related incidence of lung tumors.