I just thought I'd post an update regarding my experience after switching from dasatinib (my first-line treatment) to imatinib in May. I had to switch because of severe and rare side effects, and it seemed counter-intuitive to switch to a first generation drug. However, in my case, the following occurred:
1. Within 5 days (!) of discontinuing dasatinib and starting the imatinib, my side effects (enormously swollen lymph nodes in my neck, one the size of a golf ball) completely disappeared.
2. The lowest I ever reached on dasatinib was a BCR-Abl level of 0.04%. In three months this had halved to 0.022%.
3. I have more "quality of life" side effects now than before, and the main one that has stayed with me are the muscle cramps. But it's not bad (hope I don't jinx it by typing this!)
Anyway, the purpose of this thread is to point out that it is possible to change "backwards" from a second generation drug that was prescribed as first line treatment to a first generation drug. So far, this has worked for me.