According to the study from researchers at the Mayo Clinic and the University of Dublin, prophylactic mastectomy reduced the incidence of breast cancer in high-risk women by at least 90 percent. The findings are reported in the January 14, 1999, issue of the New England Journal of Medicine.

In this study, Lynn C. Hartmann, MD, and colleagues from the Mayo Clinic, identified 639 women with a family history of breast cancer who had undergone bilateral prophylactic mastectomy between 1960 and 1993, and compared a subset of the women with a control group of their sisters who had not had a prophylactic mastectomy. The median age at prophylactic mastectomy was 42 and the median length of follow-up was 14 years.

On the basis of family history, the researchers determined that 425 women had a moderate risk of breast cancer and 214 had a relatively high risk. Prophylactic mastectomy reduced the risk of breast cancer to 89.5 percent among the moderate-risk women and 90 to 94 percent among the women at high risk.

The reduction in risk of death from breast cancer among high-risk women ranged from 81 to 94 percent; the reduction in the risk of death in the moderate-risk women was 100 percent.

"These findings are important for women who have already undergone prophylactic mastectomy, they can now feel confident the surgery greatly reduced their risk of developing and dying from breast cancer,"says Debbie Saslow, PhD, director of breast and cervical cancer for the American Cancer Society.

"It also allows clinicians who counsel high-risk women to provide information about risk that is based on data rather than expert opinion. However, many of the women described in this study are not considered to be at high risk," she said. "It is essential that women with a family history of breast and/or ovarian cancer receive counseling from a trained professional who can help them understand their cancer risk and assess whether this drastic surgery is an option worth considering."

In an accompanying editorial, Andrea Eisen, MD, and Barbara Weber, MD, both of the University of Pennsylvania, comment on how the new report represents a major advance in our knowledge about the capability of prophylactic mastectomy to prevent breast cancer. However, they say it is ironic that the data supporting the effectiveness of bilateral mastectomy for prevention should appear in an era in which the goal of surgical treatments for breast cancer is breast conservation. The editorialists conclude that recent advances in chemoprevention, coupled with even more narrowly targeted strategies in the future, should replace prophylactic mastectomy as an option for women who are at increased risk for breast cancer.

The reasons for considering this type of surgery may include one and usually even more of the following risk factors: mutated BRCA genes found by genetic testing, previous cancer in one breast, strong family history (breast cancer in several close relatives), and biopsies showing lobular carcinoma in situ (LCIS).

This operation removes nearly all of the breast tissue, but a small amount remains. So, although this operation reduces the risk of breast cancer, it does not guarantee a cancer will not develop in the amount of breast tissue that remains after surgery.

Second opinions are strongly recommended before any woman decides to have this surgery. The American Cancer Society Board of Directors has stated, "only very strong clinical and/or pathologic indications warrant doing this type of 'preventive' operation."

Breast Cancer