Among cancer specialists today, also known as oncologists, the main theory to explain why we get cancer has to do with an original genetic mutation that causes cells to multiply uncontrollably. Cancer being a genetic disorder has been studied extensively over many decades and there are a number of holes that do not support this theory. One of the most convincing data against it is the fact that as more drugs are created to target these genetic mutations found in cancer cells, and patients are given a customized "cocktail" of these toxic drugs, the more studies show that this therapy does not prevent cancer progression and has not significantly improved cancer survival. One book I have recently read cited literature that found up to 1 million genetic mutations in one tumor, therefore in order for the current therapeutic approach to work, a patient would have to be given an enormous number of different drugs to target all of these mutations. According to Thomas Seyfried, the author of Cancer as a Metabolic Disease, there are currently approximately 700 targeted therapies developed from the cancer genome project, involved in mapping all of the genetic mutations seen in cancer, and thus far, no patient with solid tumor have been cured from this strategy.
A more convincing argument, regaining interest among a minority of cancer researchers, is that cancer doesn't begin as a genetic mutation, but instead there is damage to our ability to make energy, which then leads to our bodies requiring a change in genetic expression in order for cells to survive, and these genetic changes encourage cells to become less differentiated and multiply. Dr. Otto Warburg, a Nobel prize winner for physiology and medicine in 1931, studied cancer biochemistry and proposed that aerobic glucose fermentation, or damaged respiration involved with creating cellular energy, was the fundamental problem in cancer cells, and the cells that could adapt to using a different mechanism of creating energy would survive and become cancer cells. This theory has abundant scientific research to support it, and if we use this information to address how to prevent and treat cancer, we can come up with newer and likely more effective ways to manage our cancer epidemic.
I encourage you to read Cancer as a Metabolic Disease by Thomas Seyfried to have a better understanding of the origins of cancer, and therefore a new appreciation for other therapies. The book is technical, but well worth the time.