Prophylactic mastectomy of women at high risk of developing breast cancer has been available as one method of prevention for many years. However, little data have documented the effectiveness of this aggressive approach. Hartmann and colleagues at the Mayo Clinic conducted a retrospective analysis of women who had undergone prophylactic mastectomy at their institution over a 33-year period.

The medical records for women who had undergone prophylactic mastectomy from 1960 to 1993 were identified from the surgical index recording system at the Mayo Clinic. The starting date of 1960 was selected because it was soon after this time that breast implants became available, allowing for postmastectomy reconstruction. A total of 1,065 women underwent mastectomy during this period, and 639 of these women had a documented family history of breast cancer. This cohort of women was then divided into high-risk and moderate-risk groups. High-risk criteria included features suggestive of an autosomal dominant predisposition to breast cancer. These criteria included: two or more first-degree relatives with breast cancer; one first-degree relative plus two or more second- or third-degree relatives with breast cancer; one first-degree relative with breast cancer before age 45 and one other relative with breast cancer; one first-degree relative with bilateral breast cancer; or three or more second- or third-degree relatives with breast cancer. Three other “high-risk” groups included the criteria of ovarian cancer because of the established relationship between these two diseases.

The authors used the Gail model to predict the expected incidence of breast cancer in these women. This model is based on data from 243,221 white women who underwent annual screening for breast cancer for five years. The calculations with the Gail model include specific clinical information such as age at menarche, age of first live birth, number of previous breast biopsies and presence of a first-degree relative with breast cancer.

The women with a family history of breast cancer included 214 women in the high-risk group and 425 women in the moderate-risk group. The median age of mastectomy in all women was 42 years, with a range of 18 to 79 years. The median length of follow-up was 14 years, and the minimum follow-up was two years. Of these women, 609 (95 percent) were alive at the time the data were reviewed. Six women were found to have an incidental breast cancer at the time of prophylactic surgery. Breast cancer occurred in seven women after the surgery, with six cases confined to the chest wall at diagnosis. Among the moderate-risk group, the predicted number of breast cancers over a 14-year period was 37 cases, while the actual incidence was only four. The calculated incidence of expected number of deaths in the moderate-risk group was 10.4 cases, and the actual number was zero. In the high-risk group, the predicted incidence of death ranged from 10.5 to 30.6, depending on how the calculations were performed. The actual number of deaths in the high-risk group was only two.

The authors conclude that prophylactic mastectomy lowers the risk of breast cancer and the risk of dying from the disease. The decision to undergo this surgical procedure must be weighed against other factors, including the need for breast reconstruction, the effect on a woman's body image, the irreversibility of the procedure and the knowledge that breast cancer may never develop.