Have you discussed this with your advisor yet? Don't assume anything until you talk to him/her. I basically agree with mercapto; as long as you and your advisor can agree to de-emphasize the fact that you left a PhD program early with a MA, you'll probably be able to spin it ok. One other thing you might consider though is whether it is worth changing horses in mistream, so to speak. I say this because you probably have 2-3 years left tops to finish your PhD at this point, right? If you now go to an MSTP, you are probably going to have to begin your research all over again, and it may delay your graduation by a year or two compared to if you finish the PhD and then do a straight MD. I don't know where you're at in your schooling or whether you even care about this possibility, but I just thought I'd throw it out there for you to think about.