Many many different things cause cancer. Chemicals such as radon, asbestos, many of the chemicals in cigarettes. The sun causes cancer. Inherited genetic disorders cause cancer. Conditions like coeliac disease if left untreated cause cancer. Chromosomal translocation cause cancer. This list goes on and on. Some people are genetically predisposed to getting cancer and the along with environmental factors will cause cancer. There are many treatments for cancer, chemotherapy, radiotherapy, stem cell transfer and surgery to name a few.
On a genetic level, cancer is caused when there is a mutation in our DNA that is not ‘edited out’ by the polymerases that proofread DNA to make sure there are no mistakes. This mutation then causes cells to grow but instead of stopping when there’s the right amount, they keep on growing out of control, and make big clumps which is why cancer causes tumours. The mutations in the DNA can be brought about by any number of things, which Karen has listed comprehensively above, and there are also a large number of ways to treat it, although some types do remain harder to treat than others.