Genetically modified plants generally contain only a limited number of new components (specific DNA, RNA, and proteins) not present in conventional varieties of the same crop. These components are defined specifically by the modification being made.
DNA (and the resulting RNA) are common to all biological systems and are known not to cause cancer. Proteins are also present in all biological systems, and proteins are not considered to be causes of cancer. Certain protein hormones or toxins may have the potential to influence cancer rates as a result of their specific biological activity. However, such biological activity is predictable from protein structure and will be easily recognized in acute toxicology studies. Proteins that could cause cancer are not used in GM plants.
Thus, there is no need to undertake lifetime animal cancer studies for GM foods that contain new DNA, RNA, and proteins with well-characterized functions. Conventional foods are not subjected to lifetime cancer testing. In the event that a GM food is modified to contain some other, chemically new component, the need for cancer testing would be addressed on an individual basis, depending on the nature of the material, knowledge from other exposures to the material in the diet and biological activity.