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February 23, 2004

Double Mastectomies Significantly Lower Risk of Breast Cancer in Women
Who Are Genetically at Risk, Penn Study Shows
PROSE (Prevention and Observation of Surgical Endpoints) is First Study to Quantify
Risk Reduction for BRCA1 and BRCA2 Gene Mutation Carriers

(Philadelphia, PA) - An international study led by researchers from the Abramson Cancer Center of the University of Pennsylvania has found that a prophylactic double mastectomy - surgical removal of both breasts to prevent a cancer before it occurs - can lower the risk of developing breast cancer by 90 percent in women genetically pre-disposed to the disease. This is the first study to quantify the risk reduction for this procedure and its impact on hundreds of thousands of women in the United States who carry mutations in one or both of the two genes - BRCA1 and BRCA2 - strongly linked to breast and ovarian cancer. Their findings appear in the March 15th edition of the Journal of Clinical Oncology.

“Women are still at risk for breast cancer after any kind of mastectomy as some breast tissue remains in the body after surgery,” said lead author Timothy R. Rebbeck, PhD, Co-Program Leader of the Center’s Cancer Epidemiology and Risk Reduction Program and an Associate Professor of Epidemiology at Penn’s School of Medicine. “Now that we have quantified the benefit of a double mastectomy for reducing the chances of breast cancer, women in this high-risk group can make a better-informed decision about having breast surgery in addition to other forms of prevention, such as regular screening and/or other preventive surgeries, including ovary removal.”

The study, called PROSE (Prevention and Observation of Surgical Endpoints), followed 483 at-risk women from 11 sites in the United States, Canada, United Kingdom and the Netherlands for over six years. Most of the North American women chose not to have preventive, or prophylactic, double mastectomies. Multiple study controls were used to guard against research bias. Women who chose to have prophylactic mastectomies were paired with women in a control group based on type of mutation, treatment center and year of birth within five years. In addition, none of the participants had any previous or current diagnosis of cancer upon entering the study.

Breast cancer was diagnosed in two of 105 women (1.9 percent) who had double mastectomies. The occurrence of breast cancer was much greater in the control group, with 184 of 378 women (48.7 percent) developing breast cancer.

“The goal of future research is to refine these estimates for women in specific situations: according to the type of BRCA mutation; type of mastectomy - different procedures remove varying amounts of breast tissue; and the age and timing of surgery - many women past their child-bearing years also choose removal of their ovaries at the same time as their breast surgery,” said Rebbeck. “The decision to undergo genetic testing or have prophylactic breast surgery is a highly personal one that should be discussed with a clinician trained in counseling patients about the risks and benefits of each preventive option.”

Study results also confirmed a large risk reduction for breast cancer (95 percent) for women who also had their ovaries removed.

“Genetically pre-disposed women should also consider this procedure when evaluating their options for reducing their risk of breast cancer,” said Rebbeck.

Funding for this study was provided through a research grant from the National Institute on Health, Penn’s Abramson Cancer Center, the Breast Cancer Research Foundation, the Dana-Farber Women’s Cancers Program, the US Department of Defense Breast Cancer Research Program, the Utah Cancer Registry, the Falk Medical Research Trust, the Utah State Department of Health, and the Nebraska State Cancer and Smoking-Related Diseases Research Program.

Close to 200,000 cases of breast cancer were diagnosed in the US in 2001. The lifetime risk of any particular woman getting breast cancer is about one in eight.

Between three and 10 percent of breast cancers may be related to mutations in the genes BRCA1 and BRCA2. Women can inherit these mutations from their parents, and it may be worth testing for either mutation if a woman has a particularly strong family history of breast cancer. If a woman is found to carry either mutation, she has a greatly increased chance of getting breast cancer before age 70.

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The Abramson Cancer Center of the University of Pennsylvania was established in 1973 as a center of excellence in cancer research, patient care, education and outreach. Today, the Abramson Cancer Center ranks as one of the nation’s best in cancer care, according to US News and World Report, and is one of the top five in National Cancer Institute (NCI) funding. It is one of only 39 NCI-designated comprehensive cancer centers in the United States. Home to one of the largest clinical and research programs in the world, the Abramson Cancer Center of the University of Pennsylvania has 275 active cancer researchers and 250 Penn physicians involved in cancer prevention, diagnosis and treatment. More information about the Abramson Cancer Center is available at: www.pennhealth.com/cancer

Release available online at http://www.uphs.upenn.edu/news/News_Releases/feb04/mastectomies.htm