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
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
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
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."