Last spring, the International Agency for Research on Cancer (IARC) convened a working group that voted to classify the herbicide glyphosate as “probably carcinogenic to humans.” The vote was followed by IARC’s Press Release, a summary in The Lancet,[1] and the publication of a “monograph,” volume 112 in the IARC series.
IARC classifications of a chemical as “probably” carcinogenic to humans are actually fairly meaningless exercises in semantics, not science. A close reading of the IARC Preamble definition of probable reveals that probable does not mean greater than 50%:
“The terms probably carcinogenic and possibly carcinogenic have no quantitative significance and are used simply as descriptors of different levels of evidence of human carcinogenicity, with probably carcinogenic signifying a higher level of evidence than possibly carcinogenic.”
Despite the vacuity of the IARC’s “probability” determinations, IARC decisions have serious real-world consequences in the realm of regulation and litigation. Monsanto, the manufacturer of glyphosate herbicide, reacted strongly, expressing “outrage” and claiming that the IARC had cherry picked data to reach its conclusion. Jack Kaskey, “Monsanto ‘Outraged’ by Assessment That Roundup Probably Causes Cancer,” 43 Product Safety & Liability Reporter 416 (Mar. 30, 2015).
In the wake of the IARC classification, in the fall of 2015, the United States Environmental Protection Agency (EPA) reviewed the evidence for, and against, glysophate’s carcinogenicity. The EPA found that the IARC had deliberately failed to consider studies that did not find associations, and that the complete scientific record did not support a conclusion of human carcinogenicity. EPA Report of the Cancer Assessment Review Committee on Glyphosate (Oct. 1, 2015).
For undisclosed reasons, however, the EPA’s report was never made public until a couple of weeks ago, when it showed up briefly on the agency’s website, only to be pulled down after a day or so. See David Schultz, “EPA Panel Finds Glyphosate Not Likely to Cause Cancer,” Product Safety & Liability Reporter (May 03, 2016). No doubt the present Administration viewed a conflict between EPA and IARC, and disparaging comments about the IARC’s “process” to be national security issues. At the very least, the Administration would not want to undermine the litigation industry’s reliance upon the IARC cherry-picked report.
All joking aside, the incident highlights the problematic nature of the IARC decision process, and the reliance of regulatory agencies on the apparent authority of IARC determinations. The IARC process is toxic and should be remediated.
[1] Kathryn Z Guyton, Dana Loomis, Yann Grosse, Fatiha El Ghissassi, Lamia Benbrahim-Tallaa, Neela Guha, Chiara Scoccianti, Heidi Mattock, Kurt Straif, on behalf of the International Agency for Research on Cancer Monograph Working Group, IARC, Lyon, France, “Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate,” 16 The Lancet Oncology 490 (2015).
