The International Agency for Research on Cancer (IARC) classified n-butyl methacrylate (n-BMA) as a Group 2B carcinogen (“possibly carcinogenic to humans”) at its monograph #133 meeting in March 2023.

IARC acknowledged that there is a lack of an indication for carcinogenicity of n-BMA in humans and no mechanistic evidence underlying potential carcinogenicity was available. For example, n-BMA was clearly negative for genotoxicity in studies in vitro and in vivo. However, IARC interpreted Japanese carcinogenicity studies in a way that in B6D2F1/Crl mice, inhalation of n-BMA caused hepatocellular adenoma or carcinoma (combined) and histiocytic sarcoma of all sites in males, and haemangiosarcoma of all sites in females. Furthermore, IARC interpreted that in F344/DuCrlCrlj rats, n-BMA inhalation caused mononuclear cell leukemia of the spleen in males, and C-cell adenoma or carcinoma (combined) of the thyroid gland in females.

These tumor findings appear however to be incidental and to not provide reliable and relevant evidence for a carcinogenic potential of n-BMA in humans. As recently published, after thorough review of these bioassays, there is no convincing evidence of carcinogenicity for n-BMA, contrary to the conclusion of the JBRC and the decision by the IARC Publication.

This interpretation is consistent with the general lack of concern for cancer of Lower Alkyl Methacrylates, taking into account the considerations available from literature or expert assessment reports. For more information see Carcinogenicity– Technical Summary.

Considering the above, MPA strongly believes that the Group 2B classification for n-BMA is unwarranted and not supported by a weight of the evidence review of best available science. Available evidence as summarized above strongly shows it is highly unlikely that n-BMA can cause cancer in humans. MPA member companies stand behind the safety of their methacrylates for their intended uses. For more information

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