n-Butyl Methacrylate (n-BMA) does not pose a carcinogenic risk to humans and the classification by the International Agency for Research on Cancer (IARC) as Group 2B (“possibly carcinogenic to humans”) is not justified and not supported by a comprehensive weight of evidence review of best available science.

n-BMA was investigated in two rodent (rat & mouse) inhalation carcinogenicity studies by the Japanese Bioassay Research Center. The published study results (Furukawa et al., 2023) reported some evidence for potential carcinogenicity in both species, while acknowledging that the substance has no genotoxic potential and a mechanism of action for the reported tumor findings could not be established.

Therefore, an independent critical evaluation of the rodent carcinogenicity studies on n-BMA was conducted (Elmore et al., 2025), demonstrating a lack of a carcinogenic potential mainly based on the following findings. There are concerns on the accuracy of histopathology diagnoses and interpretation of human relevance of reported tumors. Most critically, the statistical evaluation/interpretation of all tumor types indicates no carcinogenic effects, since the frequency of increases (at p<0.05) in tumor incidences in the study is totally consistent with chance expectation (i.e. not treatment related). Further limitations include the lack of consistency of tumor findings in more than one sex-species group and lack of dose dependency. In addition, there was a lack of appropriate consideration of historical controls, including the incidences in study controls.

Taken together, considering the limitations in the n-BMA carcinogenicity studies analysis and reporting, the lack of a genotoxic potential and the absence of human data suggesting that n-BMA has carcinogenic potential, it is therefore concluded that n-BMA does not pose a carcinogenic risk to humans. Publication

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