[thaumasiotes]

Actually, a cyst meets your definition of unregulated cell growth. It's just slower / less greedy. The distinction between a benign tumor and a malignant one is generally ascertained by the process of "let's watch it and see what it does", so I'm not convinced that "cancer" is defined more usefully than "illness".

In my opinion, and my medically-educated mother's opinion (really, I get it from her), people don't look for "a cure for cancer" because they think they can make progress from that viewpoint. They do it because they're looking for funding.

edit:

You might compare "died of cancer" to "died of old age". Old age used to be an accepted cause of death. When autopsies started happening, it was quickly noticed that people who had died of "old age" always had some other, more immediate cause of death. But it turns out that if you take an old person and do your utmost to prevent / cure / treat all of those more proximate causes, eventually one will get past you and they will die.

[foobarbazqux]

Okay, but that's not actually how cysts work if you look it up. They are sacs that can have cancerous tissue inside them, but they can also have fluid or air. The operational definition of benign and malignant tumors that doctors use boils down to rudimentary observation, yes, but in the lab we've really identified many of the key mutations in the transition from benign to malignant. So I guess you could say we have a reasonably good idea of what cancer is and how it works, but it hasn't fully made its way onto the front lines yet, either in terms of assessment or treatment.

I understand your cynical point of view about funding, but I guess I would say two things. First, cynicism is a cancer unto itself (ha), and all academics are faced with the corrupting influence of money. Second, if you go and talk to the cancer researchers in the nearest university you'll probably find a great deal of them really do care about the work; they just might care about a very tiny corner of it rather than a cure-all solution.