Is there evidence that genetically modified (GM) crops cause cancer in laboratory animals?

In 2012 a paper was published that claimed that feeding rats genetically modified (GM) corn caused cancer. Not surprisingly this paper created a firestorm of controversy. Some argued that this research should lead to the banning of genetically modified organisms (GMOs) from human consumption, while others pointed out flaws in the research and asserted that there is no evidence from any study that GM corn causes cancer.

The corn in question was developed by Monsanto and is designed to be resistant to the herbicide Roundup (which is manufactured by Monsanto). This "Roundup Ready" corn contains a specific foreign non-plant gene which encodes for an enzyme that is not inhibited by Roundup allowing the plant to grow. It is important to note that this genetic modification is relatively subtle and would not be expected a priori to alter the chemical composition of the corn.

This past week the journal in which the paper was published retracted the article. The Editor-in-Chief stated that "[u]ltimately, the results presented (while not incorrect) are inconclusive, and therefore do not reach the threshold of publication for Food and Chemical Toxicology." Detailed critiques by expert scientists were much less diplomatic revealing grievous flaws in the design, collection, analysis, and interpretation of the data by the authors of the study.

Moreover, a comprehensive overview of the literature has shown that despite the large number of studies investigating whether GMOs can cause cancer (or any other disease), none has shown any dire effects from consuming them: "Results from all the 24 studies do not suggest any health hazards and, in general, there were no statistically significant differences within parameters observed." There also has not been any proposed mechanism by which a GMO can be carcinogenic. Finally, it is important to emphasize that the FDA regulates GMO food products and this regulation includes providing safety analysis.

There has been great confusion in the general public over the risks posed by genetically modified organisms. From a genetics standpoint, breeding two distant strains of corn together results in offspring that may be significantly genetically modified (different) from either parent. Approximately half of the genes of the offspring are expected to be different from either parent; this genetic variation is greater than that introduced by a single foreign gene.

However, the environmental dangers of GMOs should not be underestimated. It is possible that the transgene (foreign gene) may escape via horizontal gene transfer into other organisms in the environment. For example, the Roundup-resistant gene in Monsanto's corn could escape into the weed population so that the weeds would also become resistant to Roundup.

In summary, there is no evidence that Monsanto's genetically modified Roundup Ready corn causes cancer in laboratory animals, and more generally there is no evidence that consuming GMO products (whether plant or animal) approved by the FDA is unhealthy.

Figure 1. Monsanto's Roundup Ready GM corn does not cause cancer in laboratory rats.