Right I was browsing through Deviant art using the random button, and I came across this picture, it's of a female blazekin(that fire/fighting chicken thing) doing the move "bulk-up", I don't know if she actually grows or just brushes the feather/furry tuff off.
But it does give the appearence of Breast Expansion.
Oh, and the artist isn't half bad either.
http://www.deviantart.com/deviation/33921689/