Generally in Medicine, the diagnosis of cancer (malignancy) instantly reduces your lifespan to 5-10 years, no matter where it arises and regardless of treatment success. In most cases it's less than that. Treating cancer with the options available today is pretty much a losing battle hence all the funding, research and effort in trying to detect it early (Pap smear and PR) and in preventing it in the first place (stop smoking!!). Having said that, there always are exceptions.
Basically, if the doctor says you've got cancer, you're screwed one way or the other.
Untrue, if only because of the scores of types of cancers, the vast differences in the rates of mortality they cause, the vast differences in success with early detection and treatment, among other factors that don't lend themselves to your statistical nonsense.
The statistical reduction in lifespan is due primarily to mortality rates in the first few years after diagnoses and treatment of the most difficult types of cancers. After a number of years of being cancer-free, a person's chances of getting it again are no more than the general population. They can expect to live as long as anyone else.