Both times in a far distant past I was on low dose HRT I had gained breast tissue over and above what I naturally had. I cannot say that lost much at all, if any, over 30 years of running normal.
I am far from athletic, prone to gaining weight from just smelling food, and had a natural tendacy to being a bit bouncy up top since childhood. BTW I've basiclly been 6ft tall and 160 lbs average all those years. Earlier in life I hit a max of 250.
I suspect with all things breast and HRT related YMMV.