Genetically modified corn and cancer – what does the evidence really say?

A re-post of an article by Ashley Ng, Walter and Eliza Hall Institute, Australia

French scientist Gilles-Eric Seralini caused quite a stir last week when he claimed he’d shown cancer in rats increased when they were fed genetically modified corn and/or water spiked with the herbicide Roundup. The paper, which seven of his colleagues co-authored, was published in the peer-reviewed journal Food and Chemical Toxicology.

France’s ministers for agriculture, ecology and health responded swiftly by commissioning the National Agency for Health and Safety to look into the claims. Depending on the findings, they could invoke an emergency suspension of imports of the Monsanto GM maize strain NK603, used in the study, into Europe. Now that’s what I call high impact.

But how did the authors come to their conclusion? And can such a significant claim be made using the study data?

Rat selection

The study focuses on cancers in rats. For this they use the Harlan Sprague-Dawley strain of rat, which is known to be predisposed to getting cancer. Lots of them. Over 70% of males and 87% of females from this strain reportedly get cancer during their lifetime, whether they have been fed GM corn or not. So it shouldn’t be a surprise that so many of Seralini’s rats were found with cancer.

To make sense of this study you have to ask the simple question: “does feeding rats GM corn and/or Roundup increase the frequency of cancers compared with rats that have been given non-GM food?”

To do this, the authors of the study split up 200 rats into ten groups. One “control” group (ten male and ten female) were fed non-GM corn and had access to plain water. The researchers monitored for the development of cancer over a period of two years.

Nine other groups of twenty rats (ten male and ten female) were also monitored, but this time, these groups were given food containing 11%, 22% or 33% of NK603 GM corn, 11%, 22% or 33% of NK603 GM corn with Roundup spiked in their drinking water, or just Roundup spiked in their drinking water at different concentrations.[**Note minor correction below suggested by a reader]

The male and female rats in the control group lived for just under two years. Other studies identified that these rats die from cancer or kidney failure around this time. But the authors don’t mention this. They simply write:

“ After mean survival time had elapsed, any deaths that occurred were considered to be largely due to aging.”

They have effectively chosen not look at – and therefore don’t have to report on – why rats in the control group died. This assumption alone is sufficient grounds for rejecting this paper from publication.

Treatment group vs the control

In the study, Figure 1 (view here) shows Kaplan Meier plots the number of rat deaths by “control group” and other “treatment groups”.

What do these mean? Well, not much because the authors failed to use a statistical test to tell if there was a difference between the control groups and treatment groups.

This is important, as all their claims relate to the incidence of cancers (and other “diseases”) in the “treatment group” compared to the “control group”. These comparisons can only be made if a statistical test shows that what you observe is not happening by chance.

 

The Harlan Sprague-Dawley strain of rat is predisposed to getting cancer. jepoirrier

 

Overstating the evidence

Still on Figure 1, we see that several “treatment groups” of male rats receiving GM NK603 corn (the 22% group and 33% group) actually had fewer cancers than the male control group.

Similarly, a treatment group of male rats receiving 33% GM corn and Roundup had no difference to the control group, and two treatment groups receiving Roundup (A and C) had the same or less incidence of cancer compared with the control group.

By their perverted logic, they could equally claim that for male rats:

a) high percentages of GM corn (22% and 33%) was “protective” against getting cancer compared to group of control male rats

b) having 33% of GM corn with Roundup showed no difference to the control group and therefore wasn’t harmful to male rats, and

c) using 0.5% Roundup in the drinking water was protective against cancer in male rats compared to the the male control group.

But you can’t. You can no more make these statements than the claims about the increased incidence of cancers in the female rats in the various treatment groups. No statements can be made because no statistical test has been applied.

The full picture

One sentence that should set alarm bells ringing is the claim that “All data cannot be shown in one report.”

The retort to that statement is, “Oh yes it can. Please show it to me”. If you are reporting data, you need to show all the data.

Not enough space? Put it in the supplemental data.

In the data section, the authors show examples of pathology, histology and electron microscopy images of affected organs in the treatment groups and mention results from genetic testing of samples. All well and good, but for the genetic tests, they don’t show any data other than a statement of claim.

They also don’t present any biochemical data from the male rats – half of all their studied rats. In the legend for table 3 (which shows the “Percentage variation of parameters indicating kidney failures of female animals), they claim “Male kidney pathologies are already illustrated in Table 2” (which shows a “Summary of the most frequent anatomical pathologies observed”). But we’re not shown the raw, unmanipulated data, tested with standard statistical tests, for males and females.

Nonsensical statements

The authors then go on to describe the cancers in detail. They state:

“ Up to 14 months, no animals in the control groups showed any signs of tumors whilst 10–30% of treated females per group developed tumors, with the exception of one group (33% GMO + R).”

Well done. They have just created a non-predefined outcome measure and made a biologically nonsensical statement.

Do they mean to imply that female rats eating the highest percentage of GM corn with Roundup are mysteriously no more affected than the female control group, compared to other female “treatment groups” which were somehow more affected?

Once again, no statistical test is applied and no conclusions can be drawn.

Further, they don’t describe diseases affecting the “control group”. At all. By neglecting to state if there were any changes in the “control group”, you cannot make any statement about the “treatment groups”. That’s why you have controls.

So, what have we learnt?

This study has shown that old Harlan Sprague-Dawley rats get cancers and other diseases. This has been shown before.

What this study does not show is that exposing these rats to GM corn and/or Roundup makes any difference to the frequency of cancers or other diseases. It can’t because no statistical tests have been applied, and perhaps most worryingly, the authors do not comprehensively report on why rats in the control group died.

This study can hardly be the basis from which any government should make policy decisions or draw conclusions about the safety of the NK603 GM maize or Roundup.

Ashley Ng receives funding from the Cancer Council of Victoria, The Leukaemia Foundation of Australia and Cure Cancer Australia.

The Conversation

This article was originally published at The Conversation.
Read the original article.

 

**Comment and suggested minor correction from a reader

RE The experimental description

Nine other groups of twenty rats (ten male and ten female) were also monitored, but this time, these groups were given food containing 11%, 22% or 33% of NK603 GM corn, 11%, 22% or 33% of NK603 GM corn with Roundup spiked in their drinking water, or just Roundup spiked in their drinking water at different concentrations.

This needs minor correction according to the reader.

QUOTE “Actually the second set of three groups were the same as the first three except that the GMO corn in the second group were grown with Roundup applied in the field. Their drinking water was not spiked.

Here are the ten groups:

  • An untreated Control
  • Treated feed at 11% GMO
  • Treated feed at 22% GMO
  • Treated feed at 33% GMO
  • Treated feed at 11% GMO + RoundUp on the GMO crop during the growing season
  • Treated feed at 22% GMO + RoundUp on the GMO crop during the growing season
  • Treated feed at 33% GMO + RoundUp on the GMO crop during the growing season
  • H2O Treated with 0.1 ppb RoundUp
  • H2O Treated with 0.09% RoundUp
  • H2O Treated with 0.50% RoundUp END QUOTE

David Tribe is an applied geneticist, teaching graduate/undergrad courses in food science, food safety, biotechnology and microbiology at the University of Melbourne.

Posted in Science
22 comments on “Genetically modified corn and cancer – what does the evidence really say?
  1. pdiff says:

    Nine other groups of twenty rats (ten male and ten female) were also monitored, but this time, these groups were given food containing 11%, 22% or 33% of NK603 GM corn, 11%, 22% or 33% of NK603 GM corn with Roundup spiked in their drinking water, or just Roundup spiked in their drinking water at different concentrations.

    Just to be clear here, the second group of GM treatments were those grown with an application of RoundUp, not water spiked with RU.

  2. OgreMkV says:

    I wrote up a report as well, which goes into some detail about why these problems make the report useless. It was written for my non-science friends, but feel free to share.

    One point is that there was no mention of blind or double blind processes in the determination of cancers.

    The other thing that I also mentioned was that one of the authors is a homeopath and Seralini himself has authored books on why genetic engineering is wrong (ironic about the rats isn’t it) and organic farming, yet declared no conflicts of interest. I know, they don’t have to declare those kinds of conflicts, but it should make people really think about the source of the work.

  3. MikeB says:

    The male and female rats in the control group lived for just under two years. Other studies identified that these rats die from cancer or kidney failure around this time. But the authors don’t mention this. They simply write:

    “ After mean survival time had elapsed, any deaths that occurred were considered to be largely due to aging.”

    They have effectively chosen not look at – and therefore don’t have to report on – why rats in the control group died. This assumption alone is sufficient grounds for rejecting this paper from publication.

    I am just a simple English teacher, no training in science (though that was my dream at one time, I’m innumerate), and yet I have understood this paragraph perfectly. Assuming the information in the paragraph is correct, I have a simple question:

    WHAT THE HELL IS WRONG WITH PEOPLE?

  4. Ewan R says:

    Something else to bring up, a few French authors at one point in time critiqued safety trials of GMOs – Link to their critique

    Now, while I don’t necessarily agree with their critique one might expect that the self same authors would take it into account when designing, running and publishing an experiment.

    Apparently not though.

    As indicated above, there is no access to the data, statistically analyzed or not, their groups are tiny, they lack any description of their multivariate analysis etc.

    What are they trying to hide?! (other than their incompetence and dishonesty)

  5. David Tribe says:

    Interesting analytical comment from The Conversation website comments section to this article.

    Mark Myers
    Biomedical Science, Academic (logged in via email @ballarat.edu.au)
    https://theconversation.edu.au/genetically-modified-corn-and-cancer-what-does-the-evidence-really-say-9746#comment_77037

    Thanks for the article. The media coverage and topic also caught my attention and prompted me to read their data from the survival curves and do some stats (survival curves, Wilcoxon, using SPSS). Just for the conversation’s record, analysis of the data for the full 725 days for males fed GMO and males fed GMO+R, which are the only 2 that looked like they could be different, did not reach statistical significance.
    This should have been apparent to peer reviewers and to me this is the major concern here, which is further amplified by the controversial nature of the topic.

    • pdiff says:

      So do I understand correctly that he (M. Myers) “read” the values off the figures to run the analyses?

      On the WyoWeeds forum I suggested that it was suspicious that they had not analyzed the tumor data given that Seralini has shown past tendencies to gloat over significant results. It’s hard to imagine the authors missing an opportunity to do so here. I was immediately accused of making a personal attack, which I suppose I was, but I’ll stick by my premise. It is curious they did nothing real with this data. Perhaps this is why.

  6. ToreBKrudtaa says:

    It is incredibly interesting to see how you try to discredit the Seralini’s teams’s work. Now finally we have a really thourough toxicological study on the GM corn NK603, 700 days, and you guys at Biofortified try to make this study a joke.

    Some time ago Seralini held a very interesting lecture about the riskassessments on GMOs. In that lecture he came up with som pretty interesting information about the GMO-feeding studies done by Monsanto. Here is some of what Seralini said in that lecture:

    “In order to find statistical findings important (from feeding studies) they say they need a similarity between both sexes…. they say they need a proportional effect. They also said they have interpreted the data this way the last 50 years (GMO, chemicals, pesticides, and drugs).”

    Looks to me that the GMO-industry is fooling themselves, as well as the consumers. The whole lecture by Seralini can be seen here:

    GMO Risk Assessments Based on Bad Science – You the Guinea Pig:
    http://www.monsanto.no/index.php/en/environment/gmo/gmo-videos/190-gmo-risk-assessments-based-on-bad-science-you-the-guinea-pig

    Study linking GM maize to cancer must be taken seriously by regulators:
    http://www.gmwatch.org/latest-listing/51-2012/14245-study-linking-gm-maize-to-cancer-must-be-taken-seriously-by-regulators

    Corinne Lepage MEP on why the Seralini study is “a bomb”:
    http://gmwatch.org/latest-listing/51-2012/14233-corinne-lepage-mep-on-why-the-seralini-study-is-qa-bombq

    Shock findings in new GMO study: Rats fed lifetime of GM corn grow horrifying tumors, 70% of females die early:
    http://www.naturalnews.com/037249_GMO_study_cancer_tumors_organ_damage.html

    Learn more: http://www.naturalnews.com/037249_GMO_study_cancer_tumors_organ_damage.html#ixzz27tyobJWE

    Long term toxicity of a Roundup herbicide and a Roundup-tolerant
    genetically modified maize:
    http://research.sustainablefoodtrust.org/wp-content/uploads/2012/09/Final-Paper.pdf

    • Tore, you’d be a lot more convincing if you didn’t cite cranks like Natural News.

      • Pdiff says:

        Or fake industry sites, carrying your own article hawking Seralini’s movies and books. Is this how science is done in Europe now? Just a front for shameless self promotion, nondisclosure agreements, and media manipulation?

        Kind of makes the tag line on your fake Monsanto site more meaningful:

        Monsanto.NO – What is your choice – A sustainable world or quick profit?

  7. David Tribe says:

    Thanks for the Links Tore.

    The remarks by Corrine LePlage are wrong and misleading:.

    LEPLAGE “The strain of rats selected is not appropriate” … Interesting critique when you know it is the same strain as that used by Monsanto in its studies, which served as a basis for authorisations issued in Europe. If this strain is not valid then all authorisations must be withdrawn as they are based on ineffective tests.”
    ***The strain of rats chosen are not appropriate FOR THE EXPERIMENT THEY DID and for THEIR CLAIMS FROM IT.

    LEPLAGE: “The number of animals tested per group were insufficient” … Except that no study has ever been conducted on as many animals (200) and the number of rats per group (10 [in Seralini's case, it was 10 of each sex]) is the same as the number used in all studies submitted to public bodies and validated by them [GMW comment: Monsanto used 20 rats per group in its 90-day study on NK603 but reportedly only analysed 10! See: de Vendomois, J. S., F. Roullier, et al. (2009). A comparison of the effects of three GM corn varieties on mammalian health. Int J Biol Sci 5(7): 706–726. So Lepage is correct in saying that no industry tests on a GMO submitted for approval have analysed more than 10 rats per group]. Consequently if that number does not allow conclusions to be drawn, then none of the studies that served for GMO authorisations could be taken into account either.”

    ***Contrary to this:
    The real first long term (2 year) study of GM feed in rodents shows how such a study should be designed and presented in a scientific paper.
    http://gmopundit.blogspot.com.au/2012/09/the-first-long-term-2-year-study-of-gm.html
    This long term test of GM soy used ( five to nine times larger groups of test animals) and additional control groups, a key defect of the CRIIGEN study.

    A 104-week feeding study of genetically modified soybeans in F344 rats.
    http://gmopundit.blogspot.com.au/2012/09/the-first-long-term-2-year-study-of-gm.html
    [Article in Japanese]
    Sakamoto Y, Tada Y, Fukumori N, Tayama K, Ando H, Takahashi H, Kubo Y, Nagasawa A, Yano N, Yuzawa K, Ogata A.
    Shokuhin Eiseigaku Zasshi. 2008 Aug;49(4):272-82.
    Source
    Department of Environmental Health and Toxicology, Tokyo Metropolitan Institute of Public Health. Tokyo, Japan.

    Abstract
    A chronic feeding study to evaluate the safety of genetically modified glyphosate-tolerant soybeans (GM soybeans) was conducted using F344 DuCrj rats. The rats were fed diet containing GM soybeans or Non-GM soybeans at the concentration of 30% in basal diet. Non-GM soybeans were a closely related strain to the GM soybeans. These two diets were adjusted to an identical nutrient level. In this study, the influence of GM soybeans in rats was compared with that of the Non-GM soybeans, and furthermore, to assess the effect of soybeans themselves, the groups of rats fed GM and Non-GM soybeans were compared with a group fed commercial diet (CE-2). General conditions were observed daily and body weight and food consumption were recorded. At the termination (104 weeks), animals were subjected to hematology, serum biochemistry, and pathological examinations. There were several differences in animal growth, food intake, organ weights and histological findings between the rats fed the GM and/or Non-GM soybeans and the rats fed CE-2. However, body weight and food intake were similar for the rats fed the GM and Non-GM soybeans. Gross necropsy findings, hematological and serum biochemical parameters, and organ weights showed no meaningful difference between rats fed the GM and Non-GM soybeans. In pathological observation, there was neither an increase in incidence nor any specific type of nonneoplastic or neoplastic lesions in the GM soybeans group in each sex. These results indicate that long-term intake of GM soybeans at the level of 30% in diet has no apparent adverse effect in rats.

    Other long term studies on non GM subjects use large numbers of animals, even in the case of Ramazzini Institute who criticise the OECD protocol
    Ramazzini Institute slides are very interesting. http://bit.ly/QsDRno
    Ramazzini also use large numbers of animals (eg 90 per treatment ) in their tests, and even use larger numbers of the control animals to assure more power when making multiple comparisons
    http://www.ncbi.nlm.nih.gov/pubmed/17119234
    http://www.ncbi.nlm.nih.gov/pubmed/17805418
    http://www.ncbi.nlm.nih.gov/pubmed/17119233
    and associated papers.

  8. OgreMkV says:

    Tore,

    I’d like to add that there are several major issues with the conclusion of the Seralini paper.

    Yes, 100% of one of the test groups was killed (or died) due to cancer. But 70% of the control group were also killed (or died) due to cancer.

    What was the cause of cancer in the control group? How do you know that what caused the cancer in the control also didn’t cause the cancer in the test group?

    The answer is, you don’t. No one does. That’s why the conclusion that GM-feed causes cancer is wrong. Maybe GM-feed does cause cancer. But this study can’t show it, because it isn’t discriminatory.

    IF the control group had zero deaths due to cancer and the test groups did have deaths due to cancer in a linear fashion with the amount of GM-feed, THEN (and only then) could one make a reasonable conclusion that GM-feed causes cancer.

    However, neither of those two conditions are true. Out of 6 test groups that got the maximum dosage of GM-feed and pesticide sprayed GM-feed, 3 of them had the lowest death rate of any group (including controls) and the other 3 had the second lowest death rate of any group (including controls).

    Basically, Seralini is saying you have abetter chance of survival if you are shot twice instead of once.

    Unfortunately, since Seralini did zero statistical analysis of his results, there is no way even tell if the deaths due to GM-feed or even correlated, much less if GM-feed is the cause of the cancer/deaths.

    Sorry, but when you use rats that are bred to have cancer after about 2 years and they get cancer after about 2 years… you haven’t proven anything but that they are doing what they are supposed to do.

    • David Tribe says:

      I’d add further that CRIIGEN’s assumption of a threshold effect ( no increase at higher doses) and sex specific effect (lack of effect in one sex) is a very complicated unproven assumption. In Science a hypothesis with minimal assumptions is preferred. Complicated assumptions like this need much more data to test and they are ad hoc assumptions — made after seeing the data found do not fit with a simple model. Novel explanatations made after seeing the data are not supported by the data. They remain to be tested.

      On the other hand the “null assumption” of only random effects were made before seeing the data, and are tested in the experiment. But CRIIGEN don’t report the results of stats tests in this paper. We can assume they are negative, and in the case of animal deaths they are negative. In one other paper, CRIIGEN report similar complicated results BUT DO mention they fail to reach significance, and then proceed to ignore this failure in their discussion. They thus have a track record of ignoring failed stats tests. This is a further reason for being very skeptical about their claims and is very shoddy science.

      • Saravanan says:

        Dr.David – If you enjoy GMOs have bountiful of them to your diet. That is fine. But i want to know what i am eating want to the GMOs in food to be labelled period.

        Thanks,
        Saravanan

  9. ToreBKrudtaa says:

    (Editor’s Note: A portion of this comment was removed for violating our comment policy.)

    Science Media Centre “experts” who attacked Seralini’s study: (3)
    http://www.gmwatch.org/latest-listing/51-2012/14243-science-media-centre-qexpertsq-who-attacked-seralinis-study-3

    “UNNAMED SCIENTISTS: “Small sample size”

    GMW: Tell that to Monsanto, which in its 90-day trial on NK603 had 20 animals of each sex in each treatment dose group as opposed to Seralini’s 10, but for some strange reason, only analysed 10 of them and based its statistical analysis on this selected sample!
    de Vendomois, J. S., F. Roullier, et al. (2009). “A comparison of the effects of three GM corn varieties on mammalian health.” Int J Biol Sci 5(7): 706–726.”

    • David Tribe says:

      The trial that MONSANTO do is not a two year trial, and the claims it tests are different to those tested in the 2 year trial. Standard OECD protocols for 90 day trials are 20 rats per group, and standard OECD protocols for lifetime trials are more than 50 rats per test group.

  10. David Tribe says:

    Tore,

    CRIIGEN is not “independant” though, being funded by Auchan and Carrefour.

  11. David Tribe says:

    Here is a link to the damning commentary on the CRIIGEN report from the German Federal Government Food Saftey Research agency BfR

    http://gmopundit.blogspot.com.au/2012/10/study-of-university-of-caen-is-no.html

    No evidence of cancer and tumour due to GM corn and/or Herbicide is the Opinion of the German Government Food Safety Agency.
    QUOTE : The German Federal Institute for Risk Assessment (BfR) is of the opinion that the experimental data do not support the main statements in the publication. Further, due to shortcomings in the study design as well as in the presentation and interpretation of the data, relevant conclusions drawn by the authors are not comprehensible.

    • Pdiff says:

      Well, …. That’s pretty damning! I think the BtR needs to start reviewing for Food and Chemical Toxicology. Their reply reads exactly like the review response should have. I kept expecting to see a line in there saying “We are sorry, but we are unable to accept this study for publication in our journal”.

1 Pings/Trackbacks for "Genetically modified corn and cancer – what does the evidence really say?"
  1. [...] week later, this supposed cancer link was dropped completely by the campaign. That’s because the scientific community and science journalists together jumped on the study and laid bare its critical flaws. This led to [...]

Leave a Reply

Biology Fortified, Inc. is an independent, non-profit organization devoted to providing factual information and fostering discussion about issues in biology, with a particular emphasis on plant genetics and genetic engineering in agriculture. Find out more on our About page.

Join us as we learn about agriculture and biology with Frank N. Foode™, your friendly neighborhood genetically modified organism.

Support Biology Fortified