The Seralini paper that Monsanto objects to is still available at various places, such as the one below, but as a precaution I have taken my own copy.
It is true that the research had flaws. Although the animal groups fed the GMO-feed were large (around 90 over various dose rates etc.,), the control group contained only 10 rats. Rats just like humans get tumours as they age. The Seralini paper suggests that the age of onset of these tumours was very much reduced by feeding them GMO feed. However, there was no double-blind provision, where the people diagnosing the tumours would have had no knowledge of whether or not a rat was in a control group. And because the control group that was not fed GMO was so small, it needed only 1 odd rat to be genetically disposed to early tumours, to ensure that the results were meaningless. But that is only a 1 in 10 chance.
So the results were NEARLY statistically significant. A prudent, honest approach would be for Monsanto to run its own tests, with double-blinding and with a large enough control group, and with independent inspection.
Given their hostile attitude, I am now going organic, in order to avoid GMO-feed.
They are wanting to feed 7 billion people either with GMO food directly, or from animals raised on GMO-feed. They ought to be able to afford a few million dollars for full-scale tests over the complete lifetime of the experimental animals.