Women who undergo mastectomy of both breasts as a measure to prevent breast cancer have an exaggerated perception of their breast cancer risk before surgery, according to researchers at the Center for Research in Women's Health in Toronto, Ontario, Canada.

Prophylactic bilateral mastectomy (removal of both breasts) is a preventive option sometimes chosen by women at a high risk of developing breast cancer. Researchers compared the perceptions of breast cancer risk among women who had previously undergone prophylactic bilateral mastectomy with objective estimates of their breast cancer risk.

Researchers asked 75 women in Ontario, Canada who had undergone prophylactic bilateral mastectomy between 1991 and 2000 to provide a complete family history of the cancers that had occurred by the time of their surgery and to indicate their BRCA1 and BRCA2 gene mutation status.

Using this information, estimates were compiled of each woman's risk for breast cancer using several breast cancer risk models. Sixty of the women also provided their own estimates of their lifetime risks of developing breast cancer before and after they had prophylactic mastectomy.

The women estimated that their lifetime risk of developing breast cancer before surgery, was, on average, 76 percent and after surgery was 11.4 percent. The average estimated absolute risk reduction the women attributed to prophylactic mastectomy was 64.8 percent.

The average computer-generated risk estimates were 59 percent for the 14 women who reported that they carried a BRCA1 or BRCA2 gene mutation and 17 percent for the other women (43 had a strong family history of breast cancer and 18 had a limited family history). Breast cancer risk was statistically significantly overestimated by all women except for the known BRCA1 and BRCA2 gene mutation holders.

"Formal genetic counseling and genetic testing may result in more accurate risk perceptions to guide women in choosing other preventive options," the researchers advised.

Other sources: Journal of the National Cancer Institute