Mastectomy vs Breast Reduction for a post-cancer treated patient? (photo)

Breast reduction is more technically demanding than a mastectomy because a reduction involves maintaining vascularity to the nipple/areola and creating a pleasing breast shape. Mastectomy removes all the breast tissue down to the muscle. There is no surgery on the muscle itself in either operation.

Whether a patient has a breast reduction or standard mastectomy, no muscle is removed. Some of the milk producing tissue is left behind and re-configured after a reduction, so you keep your original tissue texture, but (usually) have to commit to a scar pattern that looks like an anchor. The nipples are kept, and usually sensation stays in tact, but can be decreased or even lost, especially around the nipple. There is still a risk of breast cancer formation, so regular screening still is required after surgery. 
With Mastectomy, the milk producing tissue is removed, but the skin is left behind. Something must be put in place under the skin so that a breast form is there- usually an implant or tissue from another part of the body, for instance- tummy tuck tissue. Sensation is virtually always lost and the scar pattern can vary widely from an anchor, to a large line that removes the nipple, to a small line that is hidden at the bra line, depending on the patient, situation, and surgeon. Regular screening with a mammogram is no longer needed following mastectomy. 
Our center performs direct to implant, nipple sparing mastectomies with incisions hidden at the bra line 95% of the time. 

A mastectomy removes all the breast while reduction reduces the size of the breast.  A mastectomy is done to treat breast cancer while a reduction is done to reduce the size of large breastsDr Corbin

The muscle has not been involved in mastectomy for over 50 years. Breast reduction is a technically more challenging operation but the healing time is about the same for both the procedures.