This week Veli-Pekka Parkkinen and I are were observing the IARC-monographs meeting on benzene in Lyon. These meetings last eight days (and nights) and aim to evaluate the evidence for the claim that benzene causes cancer. Participants are world-leading experts in the relevant areas. During the meeting they build four subgroups: Exposure, cancer in humans, cancer in animals, mechanisms and other relevant data. After evaluating their respective evidence, they meet in plenary to come to an overall conclusion by aggregating their subgroup conclusions.
Benzene’s main use is the manufacture of organic chemicals (styrene, phenol and others). Exposure is either occupational (around 1400000 exposed, in, for instance, industries like rubber and paint) or non-occupational (by, for instance, automobile exhaust and fixed industrial sources).
Benzene has been evaluated alongside other agents in several prior meetings (1981,1987 and 2009). It was categorised as Group 1 (carcinogenic to humans). This meeting is the first that exclusively deals with benzene. Although it is highly unlikely that this classification of benzene will be updated (no Group 1 categorisation has ever been changed), there are several interesting questions to be addressed in the meeting.
First, while still focussing on hazard identification, IARC wants to also provide some quantitative risk assessment. Such a quantitative risk assessment will surely be very useful for stakeholders. We are observing the “first steps” into quantitative risk assessment with a lot of interest.
Second, IARC is evaluating mechanistic evidence for the carcinogenicity of benzene. Some members of the IARC-monographs team developed the 10 key characteristics to shed some light on this very complex issue. These 10 key characteristics are distilled from all prior monographs and present most of the carcinogenic pathways for different agents. One aim of the meeting is to evaluate for each of these 10 pathways whether benzene acts through it. We are observing this part of the meeting very closely. We hope that we can get some input for our very own handbook on how to evaluate evidence of mechanisms in practice.
Finally, it is a very delicate issue to separate the effect of benzene exposure from effects of exposures to other chemicals. For instance, air pollution may cause cancer through benzene, but it might also cause cancer through various other exposures. Confounding is a really pertinent problem here and the question is which studies to include and how to weight the included studies against each other.
So far we have enjoyed the meeting very much and look forward to more interesting and stimulating discussions. And of course we have learned a lot! We wanted to thank the IARC-monographs team for giving us the great opportunity to be part of this meeting.
Words by Christian Wallman