Styrene Reasonably Anticipated to Be a Human Carcinogen, New Report Confirms


A new report from the National Research Council has upheld the listing of styrene as “reasonably anticipated to be a human carcinogen” in the National Toxicology Program’s 12th Report on Carcinogens (RoC).  The committee that wrote the report found that the listing is supported by “limited but credible” evidence of carcinogenicity in human studies, “sufficient” evidence from animal studies, and “convincing relevant information” in mechanistic studies that observed DNA damage in human cells that had been exposed to styrene.  The committee reached the same conclusion after conducting both a peer review of the RoC and an independent assessment of the styrene literature.


The NTP is an interagency program that produces the RoC.  Styrene is a substance of interest for the RoC because many people in the United States are exposed.  It is an oily, colorless to yellow liquid and it is found in many consumer products such as plastic packaging, food containers, and household goods. Sources of environmental exposure include cigarette smoke and vehicle exhaust.  Occupational exposure can occur during the industrial processing of styrene.


Based on RoC listing criteria, a substance can be classified as reasonably anticipated to be a human carcinogen based on sufficient evidence in animals or limited evidence in human studies.  In its peer review of the 12th RoC, the committee examined the primary literature cited in the document as well as other research published before June 10, 2011, and found that the RoC identified the most important studies and described the limitations and strengths of each, and that the arguments supported listing styrene as reasonably anticipated to be a human carcinogen.


In its independent assessment, the committee considered additional research published through Nov. 13, 2013.  It found that “compelling evidence” exists in human, animal, and mechanistic studies to support listing styrene, at a minimum, as reasonably anticipated to be a human carcinogen.


The committee noted, however, that there was ambiguity with respect to weighing the mechanistic evidence when applying the listing criteria, and that a strong argument could be made to support the listing of styrene as a known human carcinogen if data derived from the study of human tissues or cells alone were considered sufficient.  Further clarification and expanded guidance by the National Toxicology Program regarding the types and strength of mechanistic evidence and how it is used in the context of the RoC listing criteria is needed, the report says.



Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens is available for immediate release at  Media inquiries should be directed to the Office of News and Public Information; tel. 202-334-2138 or e-mail