Not every cancer is created equal. I helped an urologist typeset his PhD thesis about prostate cancer treatment in TeX (he used some math equations within) and he told me the same.

Some cancers are aggressive and some are slooooow. In younger patients, cancers tend to move fast and kill fast. But a slow prostate cancer in a 70 y.o. may be better left as it is, because the risks of the operation may actually be higher.

This, of course, is a difficult judgment call and belongs to the experts only.

I always wonder about bias in these statistics around age.

It makes intuitive sense to me that a cancer diagnosed in a young patient, who is below the common screening age, is probably being diagnosed because it is presenting serious symptoms (i.e. is growing fast).

Cancers diagnosed in a 70 year old, on the other hand, would seem much more likely to be diagnosed while they are asymptomatic and relatively contained, or to be cancers that have been growing slowly for a long time (more likely as the 70 year old has been alive longer).

Obviously, I don't know if this is the case or not. If anyone has experience in this field, I'd love to hear about it.