Experimental therapies will almost certainly not be covered. But scans and bone marrow would definitely be covered (if a donor could be found).
But then, I'd doubt Aetna would be too impressed if I present them with a bill for stem cell therapy here!
A good example is IVF which I am doing at the moment. In the UK you get one go on the health service. In the US most insurance does not cover this, but mine gives me $50,000 worth of treatment (about five goes).
Remember that the costs you pay for treatment are much higher (by several times) than elsewhere in the world.