In a traditional mastectomy, much of the breast skin is removed - this creates scars on the breast skin which can never be removed.
Note: ANY implant (or extender) must be covered by a layer of muscle (NOT just the skin of the breast left after a mastectomy). This is because an implant just under the skin and not covered by muscle is very visible, looks unnatural, feels unnatural, and most important, very often becomes infected.