Comment by photochemsyn

The problem of controlled cellular growth in a multicellular organism is a really hard problem that evolution has spent billions of generations on, and any cell in any of the dozens of systems that keeps the human body going can potentially escape the normal cell cycle control process and go out of control, leading to cancer. (edit: the fact that so many people lead full lives without coming down with cancer is more remarkable from this view, it's one of the miracles of life).

While the ability to treat cancer using modern technology (especially if it is detected relatively early) has made vast advances, we're also surrounded by and exposed to a wide variety of molecules that can, especially in high concentrations, inflict damage on the cellular control system (a whole lot of proteins, nucleic acids, lipids, cofactors, etc.) and while that damage may be somewhat random in nature, if it happens to hit a key sequence in the cell control DNA you get a cancer cell. You can greatly reduce the prevalance of such carcinogenic mutagens in the food, air, water and soil with suitable regulations but this cuts into profit margins for the producers of various commodities and products who in turn lobby governments to eliminate said regulations (which to be fair may not have been well-designed or implemented).

Yes there are genetic factors which may increase one's cancer risk but these are very complicated and often overemphasized by those who dont't want to see clean air, water, soil, food etc. regulations implemented.