In 2015, the International Agency for Research on Cancer (IARC) reviewed research data regarding Monsanto’s glyphosate weed killer, also known as RoundUp. The IARC, at that time, concluded that glyphosate causes cancer.
The IARC, one of the intergovernmental agencies within the World Health Organization, is widely respected for their research into the causes of cancer. And with respect to glyphosate, the IARC concluded that:
There was limited evidence in humans for the carcinogenicity of glyphosate. Case-control studies of occupational exposure in the USA, Canada, and Sweden reported increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides.
The AHS cohort did not show a signifi cantly increased risk of non-Hodgkin lymphoma. In male CD-1 mice, glyphosate induced a positive trend in the incidence of a rare tumour, renal tubule carcinoma.
A second study reported a positive trend for haemangiosarcoma in male mice. Glyphosate increased pancreatic islet-cell adenoma in male rats in two studies. A glyphosate formulation promoted skin tumours in an initiation-promotion study in mice. Glyphosate has been detected in the blood and urine of agricultural workers, indicating absorption.
Glyphosate and glyphosate formulations induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro. One study reported increases in blood markers of chromosomal damage (micronuclei) in residents of several communities after spraying of glyphosate formulations.
The Working Group classified glyphosate as “probably carcinogenic to humans” (Group 2A).
When I looked at their conclusions from a couple of years ago, I argued that there was significant evidence that glyphosate was not correlated or causal to any of the 200 or so cancers. And I wasn’t alone in that assessment.
Glyphosate causes cancer – IARC lacked evidence
Unfortunately, when the IARC made its decision two years ago, there was one major problem. According to an extensive article by Kate Kelland in Reuters, one of the members of the IARC’s study group looking at glyphosate knew of recently published data that showed no link between the weed killer and cancer. Aaron Blair, an epidemiologist from the US National Cancer Institute, never mentioned this new data to the study group examining whether glyphosate causes cancer. So the IARC made its decision without all of the available evidence.
Reuters obtained information that lead it to state that:
Previously unreported court documents reviewed by Reuters from an ongoing U.S. legal case against Monsanto show that Blair knew the unpublished research found no evidence of a link between glyphosate and cancer. In a sworn deposition given in March this year in connection with the case, Blair also said the data would have altered IARC’s analysis. He said it would have made it less likely that glyphosate would meet the agency’s criteria for being classed as “probably carcinogenic.”
The IARC acts in a manner that it appears to develop a scientific consensus about what may increase the risks of cancer. As I have mentioned many times, the scientific consensus is a powerful tool in providing us with the collective conclusions of top scientists in a field. However, this consensus must be based on evidence, not opinion or belief. And if a consensus is “proclaimed” without consideration of all of the high quality evidence, then it’s hard to put much value in it.
Now there wasn’t a grand conspiracy that blocked the IARC from considering this new evidence. Blair himself was a senior researcher on the study that showed no link between cancer and glyphosate. The reason the research wasn’t included was simple – the IARC only uses published data to come to its consensus about cancer risk, and Blair’s research could not be included in the discussion. This leads to increased transparency and reduces the risk of claims of “secret evidence” that may lead to accusations of bias.
Now, this rule may seem onerous to some, it does keep the discussion to peer-reviewed data, ignoring data that hasn’t been vetted. This probably works both ways, leaving out data that may move a chemical into a cancer causing category or not.
But this decision by the IARC had some significant consequences. First, it’s hard to read anything about GMO foods, agriculture, or food without someone spouting off that “glyphosate causes cancer.” In fact, there’s a class action lawsuit in California, with 184 individual plaintiffs, who use the IARC analysis on glyphosate, claiming that exposure to the chemical gave them cancer. The plaintiffs allege Monsanto failed to warn consumers of the risks of RoundUp, which Monsanto fiercely denies.
Monsanto claims that the fresh data should have been published in time for use in IARC deliberations on glyphosate. Or, at the minimum, the preliminary data should have been evaluated, considering Blair’s involvement with both the IARC and the new research.
Again, according to Reuters,
The company also goes beyond saying the fresh data should have been published. It told Reuters the data was deliberately concealed by Blair, but provided no specific evidence of it being hidden.
So this gets a bit more troubling.
What did Aaron Blair do? And why?
This is what is troubling to me. Actually, the data that mostly refuted the hypothesis that glyphosate causes cancer was available two years before the IARC assessment meeting. Now, science does move slowly, but that’s glacial.
According to Blair, the data was not published in a timely manner because there was too much data to fit into one scientific paper (which seems like a lame excuse to this writer). Reuters actually asked whether “he deliberately did not publish it to avoid it being considered by IARC.” Of course, Blair denied it. Furthermore, the National Cancer Institute also stated that “space constraints” was one of the reasons why the new data on glyphosate was not published in a timely manner.
Of course, the absence of Blair’s data was a critical oversight – the IARC ended the meeting by concluding that the weed killer is a “probably human carcinogen.”
In fact, the statement based its findings on “limited evidence” of carcinogenicity in humans, but “sufficient evidence” in animal research models. It specifically stated that there was a “positive association” between glyphosate and non-Hodgkin lymphoma, a cancer of the blood.
Beyond the litigation mentioned above, the IARC had all kinds of negative consequences. For example, some countries have pending decisions regarding whether to relicense or ban sales of glyphosate. Some countries have even restricted glyphosate’s use in home gardens and on crops immediately prior to harvest.
And back to the class action lawsuit in California, Reuters reports that:
… (the) California judge took the IARC assessment into account in a separate legal case in March when ruling that the state can require RoundUp to carry a warning label that it may cause cancer. Monsanto is now facing further litigation from hundreds of plaintiffs across the United States who say glyphosate gave them or their loved ones non-Hodgkin lymphoma, citing the IARC assessment as part of their claims.
All, because of an apparently flawed decision without all of the high quality evidence considered. This is frustrating from a scientific standpoint.
What is in Blair’s study?
This unpublished research, and it’s still unpublished, came from the Agricultural Health Study, a large multi-center study led by scientists at the National Cancer Institute. The researchers examined agricultural workers and their families, in the USA, who were exposed to various agricultural chemicals, including glyphosate. Blair himself agreed that the unpublished data showed “no evidence of an association” between exposure to glyphosate and non-Hodgkin lymphoma.
In fact, a review by Acquavella et al., published in 2016, examined the body of research regarding glyphosate and non-Hodgkin lymphoma. The authors concluded that, “overall, our review did not find support in the epidemiologic literature for a causal association between glyphosate and non-Hodgkin lymphoma or multiple myeloma.” That’s a pretty powerful finding with regards to the IARC decision.
Additionally, Robert Tarone also published a paper in 2016 that took IARC’s decision regarding glyphosate to task. He concluded that,
It is shown that the classification of glyphosate as a probable human carcinogen was the result of a flawed and incomplete summary of the experimental evidence evaluated by the Working Group. Rational and effective cancer prevention activities depend on scientifically sound and unbiased assessments of the carcinogenic potential of suspected agents. Implications of the erroneous classification of glyphosate with respect to the IARC Monograph Working Group deliberative process are discussed.
The IARC’s decision that glyphosate causes cancer seems to be under attack by serious researchers.
Blair admitted, while being deposed by Monsanto lawyers, that IARC’s review of whether glyphosate causes cancer would have been different if the Agricultural Health Study data were included. According to Blair, the addition of the missing data would have “driven the meta-relative risk downward.” In non-scientific terms, that means meta-data would have shown a reduced correlation between glyphosate and non-Hodgkin lymphoma.
Essentially, the IARC review ignored a huge body of robust data from a comprehensive study on exposure to glyphosate, and it’s relationship to cancers. This is a major oversight of the IARC decision.
And it’s just shocking to note that one person, Aaron Blair, was on the IARC review committee and had insider access to high quality data that refuted the IARC’s claims of correlation (and causation) between glyphosate and cancer.
Reuters took the data (which, as I stated, still has not been published, although the NCI told Reuters that they are currently working on an updated analysis) to two statistical experts to determine what it may say about whether glyphosate causes cancer. Neither of the experts had seen the data, and neither had a conflict of interest with respect to glyphosate or Monsanto.
The experts came to two key conclusions after examining the data:
- There was “no apparent scientific preseason for not publishing the data” from the large study. In other words, absent some issue like bias or bad study design, they felt that the data was publishable in its current form.
- The data shows no evidence that glyphosate causes cancer, especially non-Hodgkins lymphoma.
Of course, you’d think that the IARC would reconsider it’s decision about glyphosate, relying upon all the science, not just what they had already decided. Apparently, that’s not going to happen.
Reuters wrote to the IARC about Blair’s new data and whether they would reconsider their position. They responded by email,
IARC declined to say whether Blair informed IARC staff about the unpublished data, whether he should have, and whether that data might have changed IARC’s evaluation of glyphosate had it been published in time. The agency said it had no plans to reconsider its assessment of the chemical.
That’s not very scientific. The consensus must change with new, high quality data. It seems like the IARC is being stubborn about their decision rather than looking at more robust evidence that contradicts their conclusions.
Glyphosate causes cancer – the Summary
As I wrote in 2015, without the data from the Agricultural Health study, I, and other researchers, felt that the IARC decision was suspect. It seemed to rely upon very weak associations between glyphosate and non-Hodgkin lymphoma, while ignoring high quality evidence that showed no correlation.
With this data, as yet unpublished, the IARC’s decision about the carcinogenicity of glyphosate just doesn’t pass scientific credibility.
I hope that when Blair’s study finally gets published, the IARC will review its findings and follow the science to a more defensible conclusion. What should trouble the IARC is that many scientists are starting to look askance at their decisions regarding carcinogens. The evidence just doesn’t support their conclusions on glyphosate, but what if their decisions about other chemicals is also this badly done?
I’m convinced that we overstate the risk of cancers for lots of reasons. But there are really only a handful of ways to prevent cancer – avoiding glyphosate isn’t one of them.
Glyphosate causes cancer? The body of scientific evidence seems to say no.
Key citations
- Acquavella J, Garabrant D, Marsh G, Sorahan T, Weed DL. Glyphosate epidemiology expert panel review: a weight of evidence systematic review of the relationship between glyphosate exposure and non-Hodgkin’s lymphoma or multiple myeloma. Crit Rev Toxicol. 2016 Sep;46(sup1):28-43. PubMed PMID: 27677668.
- Guyton KZ, Loomis D, Grosse Y, El Ghissassi F, Benbrahim-Tallaa L, Guha N, Scoccianti C, Mattock H, Straif K; International Agency for Research on Cancer Monograph Working Group, IARC, Lyon, France. Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate. Lancet Oncol. 2015 Mar 20. pii: S1470-2045(15)70134-8. doi: 10.1016/S1470-2045(15)70134-8. [Epub ahead of print] PubMed PMID: 25801782.
- Mink PJ, Mandel JS, Sceurman BK, Lundin JI. Epidemiologic studies of glyphosate and cancer: a review. Regul Toxicol Pharmacol. 2012 Aug;63(3):440-52. doi: 10.1016/j.yrtph.2012.05.012. Epub 2012 Jun 7. Review. PubMed PMID: 22683395.
- Tarone RE. On the International Agency for Research on Cancer classification of glyphosate as a probable human carcinogen. Eur J Cancer Prev. 2016 Aug 22. [Epub ahead of print] PubMed PMID: 27552246.
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