SAN DIEGO--In a groundbreaking study, researchers at the Mayo Clinic have documented that prophylactic mastecto-mies may dramatically reduce the risk of breast cancer in high-risk women. The risk reduction was measured as high as 91%, lead investigator Lynn Hartmann, MD, said at the 88th annual meeting of the American Association for Cancer Research (AACR).
The researchers examined the medical records of approximately 2,500 women who had undergone a prophylactic unilateral or bilateral mastectomy from 1960 to 1993 at the Mayo Clinic.
Among these women, roughly 950 had opted for a prophylactic bilateral mastec-tomy. These women had a mean age of 43 years. They elected the surgery for a variety of reasons: family history, troubling prior breast biopsies, or nodular breasts that made accurate mammograms difficult to obtain.
The remaining 1,500 or so women had a unilateral prophylactic mastectomy after previously undergoing a mastectomy for cancer in the other breast.
Among the women who had bilateral mastectomy, 76 would have been expected to develop breast cancer over the 17 years of the study. However, only seven women actually did receive a diagnosis of breast cancer, a 91% reduction in risk.
The researchers arrived at the predicted figure by using the Gail model, which predicts the likelihood that a given woman will develop breast cancer based on various risk factors, including family history, age at menarche, age at first birth, and prior breast biopsies.
"The reduction in risk is seen in all family history groups," Dr. Hartmann said. "Those with no family history, those with some family history, and those with a very significant family history."
Two thirds of these women had some family history of breast cancer, most with a significant family history. The remaining third had no family history but had had numerous prior breast biopsies, sometimes with worrisome findings.
Researchers documented a similar phenomenon among women who underwent unilateral mastectomy. Of this group of roughly 1,500 women, only nine breast cancer cases have occurred so far. Dr. Hartmann noted that there is no comparable predictor to the Gail model for this group, but the numbers appear to be similar.
"Our findings of reduced breast cancer risk with prophylactic mastectomy are significant; however, they should not be taken as a universal recommendation for having this procedure," Dr. Hartmann said. "Rather, these data should contribute to a balanced discussion of the benefits and risks of various management strategies for individual women at high risk for breast cancer."
The Mayo study for the first time provides women and their physicians with definitive data about the effectiveness of this extreme surgery in high-risk cases. The report represents initial findings for the study, which is ongoing.
Other data are being collected on such aspects as the women's primary reasons for having the procedure, their expectations of their risk of breast cancer before and after the procedure, and the impact of the surgery on their self-esteem and body image.
Genetic testing, as it improves, should help physicians target women likely to benefit from this type of extreme intervention, if they choose it, Dr. Hartmann said. She also emphasized that genetic counseling is essential before this type of surgery can be contemplated.
"If a woman elects to proceed with the surgery, at least now we can give her some information about how effective it appears to be," she said. "But we recognize it is not a simple decision."