The big hospital near me has a huge new cancer ward. They now have qigong classes for their patients that want it.

From what I gather from talking to people, it is a case of doing something is better than doing nothing. Taking your mind off your troubles and doing something physical but not stressful or strenuous seems to help some patients get better.
I guess meditation would do the same thing, but moving qigongs allow one to feel like they are "doing something" to help themselves.

If it works, it works. It was a means to open the door and start self healing, a trigger for the body.