I have very large veins running through my breast. What happens to these veins during a breast reduction?

The surgeon will try to keep the veins intact as much as possible but if it is unavoidable, they are sometimes tied off. There are multiple levels of blood supply so these can be selectively tied if needed.

Dear lisa2027,
it is hard to tell for sure without an examination. Generally speaking, veins are cauterized often during surgery, so there should be no issues with that. If you are considering a surgery, I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Always best to ask these questions to your chosen plastic surgeon. I would respond that coagulation of, tieing of these veins is a very normal part of the breast reduction surgery.