Is the IARC Lost in the Weeds?

A couple of years ago, I met David Zaruk at a Society for Risk Analysis meeting, where we were both presenting. I was aware of David’s blogging and investigative journalism, but meeting him gave me a greater appreciation for the breadth and depth of his work. For those of you who do not know David, he is present in cyberspace as the Risk-Monger who blogs about risk and science communications issues. His blog has featured cutting-edge exposés about the distortions in risk communications perpetuated by the advocacy of non-governmental organizations (NGOs). Previously, I have recorded my objections to the intellectual arrogance of some such organizations that purport to speak on behalf of the public interest, when often they act in cahoots with the lawsuit industry in the manufacturing of tort and environmental litigation.

David’s writing on the lobbying and control of NGOs by plaintiffs’ lawyers from the United States should be required reading for everyone who wants to understand how litigation sausage is made. His series, “SlimeGate” details the interplay among NGO lobbying, lawsuit industry maneuvering, and carcinogen determinations at the International Agency for Research on Cancer (IARC). The IARC, a branch of the World Health Organization, is headquartered in Lyon, France. The IARC convenes “working groups” to review the scientific studies of the carcinogencity of various substances and processes. The IARC working groups produce “monographs” of their reviews, and the IARC publishes these monographs, in print and on-line. The United States is in the top tier of participating countries for funding the IARC.

The IARC was founded in 1965, when observational epidemiology was still very much an emerging science, with expertise concentrated in only a few countries. For its first few decades, the IARC enjoyed a good reputation, and its monographs were considered definitive reviews, especially under its first director, Dr. John Higginson, from 1966 to 1981.[1] By the end of the 20th century, the need for the IARC and its reviews had waned, as the methods of systematic review and meta-analyses had evolved significantly, and had became more widely standardized and practiced.

Understandably, the IARC has been concerned that the members of its working groups should be viewed as disinterested scientists. Unfortunately, this concern has been translated into an asymmetrical standard that excludes anyone with a hint of manufacturing connection, but keeps the door open for those scientists with deep lawsuit industry connections. Speaking on behalf of the plaintiffs’ bar, Michael Papantonio, a plaintiffs’ lawyer who founded Mass Torts Made Perfect, noted that “We [the lawsuit industry] operate just like any other industry.”[2]

David Zaruk has shown how this asymmetry has been exploited mercilessly by the lawsuit industry and its agents in connection with the IARC’s review of glyphosate.[3] The resulting IARC classification of glyphosate has led to a litigation firestorm and an all-out assault on agricultural sustainability and productivity.[4]

The anomaly of the IARC’s glyphosate classification has been noted by scientists as well. Dr. Geoffrey Kabat is a cancer epidemiologist, who has written perceptively on the misunderstandings and distortions of cancer risk assessments in various settings.[5] He has previously written about glyphosate in Forbes and elsewhere, but recently he has written an important essay on glyphosate in Issues in Science and Technology, which is published by the National Academies of Sciences, Engineering, and Medicine and Arizona State University. In his essay, Dr. Kabat details how the IARC’s evaluation of glyphosate is an outlier in the scientific and regulatory world, and is not well supported by the available evidence.[6]

The problems with the IARC are both substantive and procedural.[7] One of the key problems that face IARC evaluations is an incoherent classification scheme. IARC evaluations classify putative human carcinogenic risks into five categories: Group I (known), Group 2A (probably), Group 2B (possibly), Group 3 (unclassifiable), and Group 4 (probably not). Group 4 is virtually an empty set with only one substance, caprolactam ((CH2)5C(O)NH), an organic compound used in the manufacture of nylon.

In the IARC evaluation at issue, glyphosate was placed into Group 2A, which would seem to satisfy the legal system’s requirement that an exposure more likely than not causes the harm in question. Appearances and word usage, however, can be deceiving. Probability is a continuous scale from zero to one. In Bayesian decision making, zero and one are unavailable because if either was our starting point, no amount of evidence could ever change our judgment of the probability of causation. (Cromwell’s Rule) The IARC informs us that its use of “probably” is quite idiosyncratic; the probability that a Group 2A agent causes cancer has “no quantitative” meaning. All the IARC intends is that a Group 2A classification “signifies a greater strength of evidence than possibly carcinogenic.”[8]

In other words, Group 2A classifications are consistent with having posterior probabilities of less than 0.5 (or 50 percent). A working group could judge the probability of a substance or a process to be carcinogenic to humans to be greater than zero, but no more than five or ten percent, and still vote for a 2A classification, in keeping with the IARC Preamble. This low probability threshold for a 2A classification converts the judgment of “probably carcinogenic” into a precautionary prescription, rendered when the most probable assessment is either ignorance or lack of causality. There is thus a practical certainty, close to 100%, that a 2A classification will confuse judges and juries, as well as the scientific community.

In IARC-speak, a 2A “probability” connotes “sufficient evidence” in experimental animals, and “limited evidence” in humans. A substance can receive a 2A classification even when the sufficient evidence of carcinogenicity occurs in one non-human animal specie, even though other animal species fail to show carcinogenicity. A 2A classification can raise the thorny question in court whether a claimant is more like a rat or a mouse.

Similarly, “limited evidence” in humans can be based upon inconsistent observational studies that fail to measure and adjust for known and potential confounding risk factors and systematic biases. The 2A classification requires little substantively or semantically, and many 2A classifications leave juries and judges to determine whether a chemical or medication caused a human being’s cancer, when the basic predicates for Sir Austin Bradford Hill’s factors for causal judgment have not been met.[9]

In courtrooms, IARC 2A classifications should be excluded as legally irrelevant, under Rule 403. Even if a 2A IARC classification were a credible judgment of causation, admitting evidence of the classification would be “substantially outweighed by a danger of … unfair prejudice, confusing the issues, [and] misleading the jury….”[10]

The IARC may be lost in the weeds, but there is no need to fret. A little Round Up™ will help.


[1]  See John Higginson, “The International Agency for Research on Cancer: A Brief History of Its History, Mission, and Program,” 43 Toxicological Sci. 79 (1998).

[2]  Sara Randazzo & Jacob Bunge, “Inside the Mass-Tort Machine That Powers Thousands of Roundup Lawsuits,” Wall St. J. (Nov. 25, 2019).

[3]  David Zaruk, “The Corruption of IARC,” Risk Monger (Aug. 24, 2019); David Zaruk, “Greed, Lies and Glyphosate: The Portier Papers,” Risk Monger (Oct. 13, 2017).

[4]  Ted Williams, “Roundup Hysteria,” Slate Magazine (Oct. 14, 2019).

[5]  See, e.g., Geoffrey Kabat, Hyping Health Risks: Environmental Hazards in Everyday Life and the Science of Epidemiology (2008); Geoffrey Kabat, Getting Risk Right: Understanding the Science of Elusive Health Risks (2016).

[6]  Geoffrey Kabat, “Who’s Afraid of Roundup?” 36 Issues in Science and Technology (Fall 2019).

[7]  See Schachtman, “Infante-lizing the IARC” (May 13, 2018); “The IARC Process is Broken” (May 4, 2016). See also Eric Lasker and John Kalas, “Engaging with International Carcinogen Evaluations,” Law360 (Nov. 14, 2019).

[8]  “IARC Preamble to the IARC Monographs on the Identification of Carcinogenic Hazards to Humans,” at Sec. B.5., p.31 (Jan. 2019); See alsoIARC Advisory Group Report on Preamble” (Sept. 2019).

[9]  See Austin Bradford Hill, “The Environment and Disease: Association or Causation?” 58 Proc. Royal Soc’y Med. 295 (1965) (noting that only when “[o]ur observations reveal an association between two variables, perfectly clear-cut and beyond what we would care to attribute to the play of chance,” do we move on to consider the nine articulated factors for determining whether an association is causal.

[10]  Fed. R. Evid. 403.

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