Where have you read that cows are genetically re-engineered? What nonsense! (sorry for my reaction) There are no cows re-engineered!.........please don't believe all that nonsense if you had read it somewhere.
'Engineered' food doesn't always mean it is bad for us, food engineering has always been done by humans since the invention of agriculture, beer, tofu, cheese making are some examples of bio-engineering.
We also eat natural mutants (broccoli, cauliflower), corn and rice that we eat now are not 'natural' anymore as they had already been bred to suit our taste using traditional plant breeding. The new Molecular Breeding by inserting certain genes is just a simplification of that traditional breeding and is actually less dangerous as we introduce less unwanted genes as compared to traditional breeding (through crossing).
Food plays an important role in the development of cancer, as well as the environment, some people are also more inclined genetically to develop cancers, smoking increases
the chances of developing cancer.
Also, the level of your immune system is important whether your own body can defend against the development of cancers inside your body (we have a repair system in our cells to defend ourselves against cell damage as well as DNA damage, which in many cases could lead to cancers).
Fish is I think much healthier than eating red meat, and healthy regular exercise will increase our immune system, also being too clean is I think not so good as that reduces our immune system.