Oversimplified but: According to my education, cancer is the result of an evolutionary trade-off. We need cells to regenerate so we can continue living. They do this often. Sometimes they make mistakes. Some mistakes can be deadly. To prevent mistakes from causing trouble, cells have error checking mechanisms. When mistakes are caught, the cell needs to self-destruct. This system works quite well most of the time. With one exception, errors occurring at any point during this process will all be effectively voided out. The exception is when the error is such that the self-destruct mechanism is damaged. Then, erroneous cells are able to replicate and it may get out of hand. We call this cancer.
Oversimplified but: According to my education, cancer is the result of an evolutionary trade-off. We need cells to regenerate so we can continue living. They do this often. Sometimes they make mistakes. Some mistakes can be deadly. To prevent mistakes from causing trouble, cells have error checking mechanisms. When mistakes are caught, the cell needs to self-destruct. This system works quite well most of the time. With one exception, errors occurring at any point during this process will all be effectively voided out. The exception is when the error is such that the self-destruct mechanism is damaged. Then, erroneous cells are able to replicate and it may get out of hand. We call this cancer.
That is one explanation, but there is a lot we don't understand about the body.
There is a lot big pharma does not want us to understand.
This is my understanding as well.