Many great answers. Cancer is also caused by eating foods that contain Hydrogenated Oils or any trans-fats. These types of man-made preservative can cause the cells to begin to mutate, especially when eaten in great quantities there is more opportunity for this. This mutation of cells can then become the precursors for the onca-genes to form. These onca-genes can then begin to proliferate into a mass of mutated cells. If not removed they will at times proliferate at a rapid speed and go further out of control. (Often people think of these cells as having a mind of their own, but they are really onca-genes that began from some mutated cells.) By the way, we all have some mutated cells, but most of the time these do not become precursors for the onca-genes. Mutated just means that during Meiosis and Mitosis cell division the transfer of chromosomes did not go the normal route. If you recall your cell division activities, you know what I am talking about. It could occur during the Anaphase, Metaphase, Telophase or some other time of cell division.
Laura Lewis, MS, ACSM, NASM (My undergrad work was in Genetics, Biology, Inorganic and Organic Chemistry, Kinesiology, Anatomy and Physiology etc.)