Authored By:

International Agency for Research on Cancer

The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO) and is responsible for assessing and classifying agents for their potential to cause cancer in humans. Initially, IARC was formed to classify the carcinogenicity of chemicals; however, the scope has since broadened to other agents including complex mixtures, physical agents (which includes radiation), biological organisms, pharmaceuticals, and other exposures. Expert working groups are set up to examine and classify the cancer risk of the agents being assessed. A preamble outlines the requirements of the identification, assessment and classification process. The preamble describes how a working group should gather and assess the evidence of carcinogenicity of the agent being considered and the role of the participants. Further, the preamble is also designed to promote transparency surrounding the evaluation process so the scientific community and the public can understand the decision of the working group.

The first part of the preamble characterises the exposure to the agent including descriptions of the physical quantities of the agent and the exposure scenarios in the environment. This part also includes a discussion of current regulations and a critical review of the exposure assessment in key epidemiological studies. There are three major categories used to examine the evidence of carcinogenicity. These categories include:

  • carcinogenicity in humans
  • carcinogenicity in experimental animals
  • mechanistic evidence

A working group aims to thoroughly research and evaluate the available evidence of cancer risk from an agent within these categories.  

The final section of the preamble is an overall evaluation that discusses the evidence assessed and places the agent in set risk categories. The risk categories currently include:

  • Group 1 - the agent is carcinogenic to humans
  • Group 2A -the agent is probably carcinogenic to humans
  • Group 2B - the agent is possibly carcinogenic to humans 
  • Group 3 -the agent is not classifiable as to its carcinogenicity to humans

Recently IARC have updated the preamble for classifying carcinogenicity (IARC, 2019). The evaluation process in the reviewed 2019 IARC preamble has some key changes to its last revision in 2006 (IARC, 2006). One key change to the preamble is a strengthening of the evaluation process to make it more prescribed, for example, assessing the quality of the studies has been broken into seven well-described parts. This refining of the assessment methodology should increase the consistency and transparency of the evaluation process. Another key change is the addition of a table by Smith et al, 2016 describing key characteristics of an established carcinogen that can be used to help evaluate the mechanistic evidence. A small change was the removal of the group 4 classification, which was used to classify an agent as probably not carcinogenic to humans. This implies that IARC classifications now only include agents that have been confirmed as carcinogenic or display varying degrees of evidence and are still being assessed.

IARC has to date classified the carcinogenicity of over a thousand agents. The identification of an agent as carcinogenic may have a significant impact on society or the processes that result in exposure to the agent. Further, IARC’s classification does not include an assessment of exposure levels. Consequently, there is no consideration of dose or exposure level to which an agent begins to be carcinogenic. Therefore, the assessment is limited to whether the agent is or is not carcinogenic. This means that, with the appropriate control mechanisms, exposure to an agent may be possible with minimal risk of harm.

In 2013, IARC examined the evidence of carcinogenesis from radiofrequency electromagnetic fields. The results of the assessment were published in the IARC monograph “Non-ionising Radiation Part 2: radiofrequency electromagnetic fields Volume 102”. The overall evaluation found that radiofrequency electromagnetic fields are possibly carcinogenic to humans (Group 2B). This decision was based on limited evidence from epidemiological studies, which showed an increased risk of brain tumours among heavy mobile phone users. IARC noted at the time of the decision that the occupational and environmental exposures provided inadequate evidence of a cancer risk.

Periodically an IARC advisory group meet to make recommendations for what agents should be evaluated or re-examined for their carcinogenicity. In March 2019, recommendations for evaluations to be conducted in the 2020-2024 period were published in the Lancet Oncology journal. The list of recommendations included a re-assessment of radiofrequency electromagnetic fields (IARC, 2019). The rational for this re-evaluation was stated by IARC to be new bioassay and mechanistic evidence.

Published In:

IARC Monographs on the Identification of Carcinogenic Hazards to Humans
Commentary by ARPANSA:

ARPANSA fully supports the work of IARC and the revision of its preamble as it increases the transparency of the scientific evaluation process.

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