Are you transgendered? Just wondering.
I don't know what you can expect. I still think a doctor will be able to tell you more.
If you had hormone replacement therapy then you are unlikely to get large breasts anyway. So I would not worry about that so much.
But this won't just affect your breast tissue, as lilacwoman said, it will get into your blood stream and have an impact on the rest of your body too. If you have enough to grow some breast tissue you might also expect results such as lower libido, errectile dysfunction, loss of muscle mass, depression (particulalry if you are not trans), lower energy, increased risk of blood clots, moodyness, .... altertnatively nothing might happen as it has to compete with your testosterone.
Progesterone creams are absorbed in varying amounts by different people so that for some they are getting an ineffective dose and for others they are receivig an overdose. It may also cause you to become hairier and increase your risks of breat cancer.
The creams work by getting into your blood, not just where you put them. I'm guessing you could rub them on your abdomen and get similar results i,e, effects your whole body. (Interestingly my patches say never to place them on your breasts. Perhaps this is because it increases the risk of breat cancers?? Who knows)