The women isn’t trans, and the joke is that the breasts HAVE to go somewhere. When people get top surgery they don’t do a transplant lol.
Cis women get breast reduction done all the time, often to reduce chances of developing back problems, but I believe it’s recommended if you’re in a high risk group for breast cancer. But yeah the absurdist element of putting the breasts somewhere is a bit weirder when you don’t know the context of the heart transplant comic.