[thaumasiotes]

Yes, I meant PaulHoule's comment. If the reason for studying "cancer" is that "cancer" is more widespread than better-defined illnesses, then the reasoning is misplaced; it's surely better to focus on something more widespread, like "illness".

I have seen it expressed, though not in these terms, that asking for a "cure for cancer" is equivalent to asking for bug-free software. Cancer isn't something that afflicts you from without; it's just a failure mode for cells. They can fail for all kinds of reasons (indeed, note that one of our best methods of causing cancer, radiation, works on the principle of "make random changes to the cell's genetic code, and it will eventually become cancerous").

[foobarbazqux]

So I think the general claim is that focusing on cancer is a middle ground between seeking treatments for obscure well-defined illnesses and searching for a panacea for illness or disease in general. Cancer has a precise operational definition: unregulated cell growth. It isn't nearly as vague as illness or disease. We understand a lot about all the different pathways inside cells that can lead to it. A "cure for cancer" is an attempt to address the issue upstream, such that it will affect all different types of cancer in the body. Unlike seeking a panacea for all illness, this is not obviously a waste of research effort. There are highly similar mechanisms at work in every cancer. Even if a cure-all cannot be found (I would be surprised, personally), just trying to understand the mechanisms still has value.

[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.