The IARC re-classification of talc carcinogenicity: a move in the wrong direction?

The paper explores a content of the recent International Agency for Research on Cancer (IARC) Monograph (Volume 136) where pure talc was reclassified from the Group 2B (“Possibly carcinogenic to humans”) to the Group 2 A (“Probably carcinogenic to humans”). The Monograph is considered in the context of the history of the IARC program for classification of carcinogens as well as in the framework of basic principles of toxicological science. It is demonstrated that reclassification was made not based on any new scientific information available, but rather because of a change in some of the methodological approaches or preferences employed by IARC. In particular, it is demonstrated that there are significant mineralogical issues in characterization of talc by the recent IARC Monograph. It is shown why weight-of-evidence for carcinogenicity of pure talc in experimental animals cannot be estimated higher than “limited”, and in human study higher than “inadequate”. It will also be argued that utilization of separated mechanistic criteria (key characteristics of carcinogens) without contextual analysis and proven mode-of-action (MoA) can cause significant uncertainties in the determination of carcinogenicity in humans. There is a need for comprehensive risk assessment for various agents and processes, rather than just hazard identification that the IARC continues to exercise with questionable relevance for global cancer prevention.