Patients may be asked to donate blood prior to the procedure in case a transfusion becomes necessary later. They should tell their physician about all medications they are taking to ensure that none of them will interact adversely with medications used during surgery. Patients usually are asked not to eat or drink anything for eight to 12 hours prior to surgery.

Patients undergoing a mastectomy usually will be placed under general anesthesia and will be asleep during the procedure. The surgeon will make an incision into the breast, which may extend to the armpit if lymph nodes are to be removed. Breast tissue between the overlying skin and underlying muscle is removed, with the extent of tissue removal varying depending on which type of mastectomy is being performed.

• Partial mastectomy. Tissue is removed in triangular wedges all the way down to the level of the muscle. The remaining tissue and skin are then sutured (stitched) together.
  
  
• Modified radical mastectomy. The surgeon makes an elliptical incision and removes the nipple and the scar from the breast biopsy. This is known as a skin-sparing incision that tries to limit the amount of skin removed as a means of enhancing a future breast reconstruction. The surgeon then tunnels under the skin up to the collarbone (clavicle) and down to the border of the ribs, and between the middle of the breastbone (sternum) and out to the muscle behind the armpit. The breast is peeled off, leaving the muscle behind.
  

If lymph nodes are being removed, this will be done as part of either a sentinel node biopsy or axillary dissection. Following the removal of the breast and lymph nodes, the flaps of skin are joined and sewn together.

A mastectomy can take up to two to five hours. Depending on the procedure, a mastectomy may be outpatient surgery, or the patient may be admitted to the hospital. In most cases, women having mastectomies will spend one or two nights in the hospital, or may be placed in a short-stay observation unit with follow-up care provided by a home care nurse.