Yes, lots of us have switched from imatinib to dasatinib. Informally, and anecdotally, it SEEMS that many people who hate the side effects from a full dose of imatinib (400) find great relief when they switch to dasatinib. And vice versa! It SEEMS that people fall in one camp or the other, but not both. Anyway, back to facts. Dasatinib has an excellent track record for response, so I think your son will see a downward trend in his PCR. 100 mg is still the recommended starting dose, although there are studies to show 50 mg is just as effective, but he will be OK on that for awhile, don't worry. BUT, when he gets a nice response and gets down to 0.1 or lower, then yes, he should promptly be moved to 50 mg. This is because at least a third of dasatinib users develop pleural effusion and it is thought that the higher the dose, the more likely that will happen. Now, having said that, pleural effusion can be a non-symptomatic, mild side effect. People living with long-term minimal residual fluid (and remember, this is in the LINING of the lungs, not IN the lungs), like me, maybe have something to worry about in the future by staying with dasatinib for decades - we don't know - but I have maintained 0.005% IS (at least) for the past several years, and I'm happy to live with the fluid, which doesn't affect me in any way on a daily basis. All other side effects are so, so, so minimal compared to the misery I endured on imatinib 400 mg (although it worked against the CML.) I've been at this 12 years btw. I second the advice to avail yourself of further consultation with the CML experts, but I do think that your son is doing well and will continue to do well. I hope that in his lifetime there will come a true cure.