You're not wrong. Think of cells as a factory making a product. In cancer, not only is the product wrong but you can't shut off the factory. Also why cancer is so awful if you get it younger. To go back to the factory analogy, in a young person, the factory is shiny and new and efficient, so it makes the cancer really fast. Whereas in an older person, the factory already isn't in the greatest of shape, even before the cancer.