Soy products shouldn't have carcinogens, not that I know of, because Soy contains Phyto-oestogens that are similar to Oestrogen, attach to receptors and block the effects of excess Oestrogen, which include Gynocomastia, blood clots and breast cancer.
So if genetically modified Soy has carcinogens in it, then I suspect it's been made in some really bad way.
The only other explanation is, is that the product is cooked in some kind of fatty substance with a poor smoke point, I.E. Flaxseed Oil for example.
Oils that exceed the smoke point temperature duing cooking, can undergo a toxic conversion and become carcinogenic, so anything you cooked with them that created this scenario, could become carcinogenic, as most fats and oils will saturate into many things you cook.