Tranfer from DO to MD program

Is it possible to tranfer from a DO program after your first year into an MD program?
Have you hear of such a situation??

The short answer: Probably NO. There was a discussion about this a long time ago, in which someone had found out that MD programs might not accept the credits earned in a DO program because, although the programs are virtually identical, the agencies that accredit the programs are different.
Transfers while in med school - whether it’s a DO or MD program - are RARE. My impression has been that there has to be a “good reason.” For example, I have two classmates who transferred because their spouse/s.o. got a job here in Washington. No one should anticipate a med school transfer as a way to “trade up,” whether it’s within the MD or DO ranks, or, say, from Caribbean school to US school.
It is hard not to speculate at the motivation behind your inquiry. NO ONE should EVER accept a spot at a DO school with the anticipation that it might be possible to transfer to an MD program. If DO seems an unpalatable plan for whatever reason, then don’t go.

Like Mary pointed out, it is possible, but extremely unlikely! KCOM, where I attend, had a girl from the class of 2002 transfer into an MD school in the Chicago region…but she had to have substantial documentation for why. If I correctly recall, it had something to do with health issues of one of her parents. She was able to transfer into that school's 3rd year after completing her 2nd year here.
Again, as Mary points out, transferring from any school to another one, irrespective of MD or DO, is extraordinarily difficult. They will mandate far more indepth reasons than convenience or that you simply wanted to do so.