I’d expect all sorts of cancer risks. Not just breast cancer.
But it’s not like they have ovaries, a uterus or any other girl parts so it’s not the SAME risk as a normal woman, obviously.
The use of these female enhancing hormones may produce the breast they want, but there are trade-offs: prostrate cancer, heart disease, blood clots, type II diabetes, pituitary tumors, loss of libido and other slaps in the face by nature. If their gender reassignment has turned them into an ugly female, they risk living a lonely and unloved life that they would not have had as a male.