In September 2012, Food & Chemical Toxicology published a peer-reviewed study purporting to show that rats fed genetically modified corn had a higher incidence of tumors than those that were not. This was significant, as this study was the first to find evidence of an adverse health effect in any mammal species from the consumption of GM foods. The study immediately faced a wave of criticism from scientists and experts in the field, who noted the paper’s many methodological failings. In response to such criticism, Food & Chemical Toxicology retracted the paper on November 28, after the paper’s authors refused to withdraw it on their own. The authors are now threatening suit against the journal, and anti-GMO activists are organizing a boycott, but the editors are standing their ground.
UPDATE: Hoisted from the comments, here’s more from Ars Technica, and an early critique of the study at Respectful Insolence.