In 2012, Séralini et. al. published their study (Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize) claiming to show an association between cancer in rats and corn genetically engineered to be resistant to glyphosate (including some groups to which he actually fed glyphosate). The scientific community at large quickly condemned the study due to numerous obvious failures in its methods, and the Wakefieldian, (Or Ponz and Fleschmannian if you prefer) style of the researchers in manipulating the press before the scientific community at large had a chance to evaluate the study....

from Prof. Anthony Trewavas FRS:

Seralini’s whole results depend totally on an inadequate number of control rodents. To do this research properly several thousand rodents at least would be needed. There is nothing in these results except random error and any competent referee would have picked up that immediately.

and:

I also question the absence of control photographs and whether it is ethical to keep rodents in those conditions just to provide pictures that can be used as frankly nothing more than propaganda. Science requires the dispassionate presentation of information-this paper and this journal have dealt the value of evidence-based knowledge a serious blow and it can only be rectified if the paper is withdrawn by the authors with an apology for misleading the public and the scientific community alike.

...From Frederic Schorsch’s paper, entitled: Serious inadequacies regarding the pathology data presented in the paper by Séralini et al. (2012)

This article attracted great attention within the scientific and regulatory community. Substantial gaps in the study design, fundamental flaws in the data analysis and erroneous interpretation of results have been pointed out by individual scientists and administration bodies. Upon request by the European Commission, the European Food and Safety Authority (EFSA) reviewed the study and concluded that the design, reporting and analysis of the study as presented in Food and Chemical Toxicology are inadequate and that this contribution is of insufficient scientific quality to be relevant in the safety assessment process

From the European Food Safety Authority:

Considering that the study as reported in the Séralini et al. (2012) publication is of inadequate design, analysis and reporting, EFSA finds that it is of insufficient scientific quality for safety assessment. Therefore, EFSA concludes that the Séralini et al. study as reported in the 2012 publication does not impact the ongoing re-evaluation of glyphosate, and does not see a need to reopen the existing safety evaluation of maize NK603 and its related stacks. EFSA will give the authors of the Séralini et al. (2012) publication the opportunity to provide further information on their study to EFSA.