Breast reduction and fat transfer to butt. What are the risks of doing this?

Hi... thank you for the question.... If you have big breast (like you are saying)... and a PS practice a liposuction on them, there are some risk like loose skin, the amount of fat tissue is not going to be enough for a BBL... I suggest you a  consultation by photos or physical with a board certified plastic surgeon to study your case..

Fat can be used from other body parts. I don't know anyone who would take fat from the chest to inject into the buttocks.