November 6, 2024
A recently published commentary authored by Gradient scientists evaluates the epidemiology, experimental animal, and mechanistic evidence behind the IARC’s recent PFOA and PFOS cancer classifications.
In November 2023, the International Agency for Research on Cancer (IARC) finalized its evaluation of the carcinogenicity of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), classifying PFOA as Group 1 (“carcinogenic to humans”) and PFOS as Group 2B (“possibly carcinogenic to humans”). Gradient scientists recently published a commentary on this evaluation, in which they assessed the epidemiology, experimental animal, and mechanistic evidence used as the basis for IARC’s conclusions.
Specifically, the commentary addresses IARC’s approach for considering mechanistic evidence in assessments of potential carcinogenicity. The mechanistic evidence for PFOA and PFOS was used to upgrade IARC’s classifications for these substances to higher carcinogenicity categories than were initially determined from the epidemiology and experimental animal evidence. For example, PFOA was initially classified as Group 2A (“probably carcinogenic to humans”) based on limited epidemiology evidence and sufficient experimental animal evidence, but was upgraded to Group 1 after consideration of mechanistic evidence. Similarly, PFOS was initially classified as Group 3 (“not classifiable as to its carcinogenicity”) based on inadequate epidemiology evidence and limited experimental animal evidence, but was upgraded to Group 2B after consideration of mechanistic evidence. The Gradient authors demonstrated that IARC’s approach did not consider the quality, external validity, and relevance of the mechanistic evidence and concluded that IARC’s approach for evaluating mechanistic evidence did not constitute a systematic or robust mechanistic assessment of carcinogenicity. Further, the authors concluded that IARC overstated the available evidence for the carcinogenicity of PFOA and PFOS.
The commentary goes on to discuss that the classification of a substance as carcinogenic to humans by IARC, or other agencies, does not consider how much exposure to the substance is needed to cause cancer and, therefore, does not necessarily indicate that the substance will cause cancer at human-relevant exposure levels and pose a public health concern.
Read the commentary here: “Commentary: Understanding IARC’s PFOA and PFOS Carcinogenicity Assessments“