Anyway, the only reason that we lose "only 3 years" to cancer is that something else is going to kill us not long after if cancer doesn't. However, if we were able to prevent all other forms of death, cancer would still kill all of us eventually.

I tend to think of curing cancer as not just "adding 3 years of life", but as a small but vital part of developing extreme medical (that is, organic) longevity.