Breast reduction surgery (reduction mammaplasty) has been found to reduce the risk of breast cancer by reducing the amount of breast tissue that could develop cancer. The injury to the breast caused by the surgery, and the attendant scar tissue, do not increase breast cancer risk, according to available research.

Postmenopausal women benefit more from breast reduction surgery

Generally speaking, breast reduction surgery appears to provide a more immediate decrease in breast cancer risk for postmenopausal women than premenopausal women. For postmenopausal women, breast cancer risk increases with increasing body mass index, waist-hip ratio, waist size, and weight gain.
On the other hand, being overweight (and hence more likely to have large breasts) is protective against breast cancer before menopause, a finding reported by numerous breast cancer studies, but not adequately explained. One study found that a large bra cup size at a young age was associated with a higher risk of premenopausal breast cancer, but only for leaner women with body mass index less than 25. In other words, premenopausal women whose breasts are large primarily because they are overweight do not have a higher risk of breast cancer (and therefore would not be expected to benefit as much from breast reduction surgery).

Breast reduction surgery for cancer patients or high risk women

Breast reduction surgery can make sense for large-breasted women who are diagnosed with early stage breast cancer. Rather than opting for breast conserving surgery such as lumpectomy, such women can elect to have breast reduction surgery, thereby removing the tumor and reducing their risk of new tumors in subsequent years, as well as eliminating the discomfort associated with having large breasts. Breast reduction surgery has also been proposed as an alternative to prophylactic bilateral mastectomy for high risk BRCA1 or BRCA2 breast cancer gene mutation carriers.