The International Agency for Research on Cancer (IARC) categorises chemicals with regard to carcinogenicity into the following groups: Group 1 (‘agent is carcinogenic to humans’), Group 2A (‘agent is probably carcinogenic to humans’), Group 2B (‘agent is possibly carcinogenic to humans’), Group 3 (‘agent is not classifiable as to its carcinogenicity to humans’) and Group 4 (‘agent is probably not carcinogenic to humans’).
While IARC does not specifically consider the mechanism of lung overload in rats as a species-specific effect which is not relevant to humans, it recognised the issue of excess incidences of lung cancer in rats after chronic inhalation of overloading doses of PSP in context of its evaluation of the carcinogenicity of carbon black, titanium dioxide and talc. It highlighted the need of assessing the scientific evidence allowing for comparison of exposure, dose-response and mode of action among the different species. IARC further proposed a conceptual framework of carcinogenesis induced in the lungs of rats after high exposure to PSPs. (IARC, 2010).