The risk for a new cancer in the unaffected breast substantially increases in women diagnosed with unilateral, hereditary (non-BRCA) breast cancer, according to a new study.

Published in the March 15, 2006 issue of CANCER, a peer-reviewed journal of the American Cancer Society, the study reveals women under 50 diagnosed with hereditary (non-BRCA) breast cancer are at significantly greater risk for developing cancer in the other breast, also known as contralateral breast cancer (CBC). Adjuvant hormonal therapy, however, reduces CBC risk.

Women with hereditary (non-BRCA) breast cancer are estimated to be at up to six times greater risk of developing a second primary malignancy in the other breast than the general population is of developing primary breast cancer. Young age at first diagnosis, family history of breast cancer, and confirmed BRCA1 or BRCA2 gene mutations are the primary risk factors for CBC. However, the contribution of non-BRCA hereditary cancers to the risk of CBCs is poorly understood.

Led by Katarina Shahedi, M.D. of the Umee University and colleagues at the Karolinska Institute in Stockholm, Sweden, researchers reviewed data from 120 families and 204 women with unilateral breast cancer and a family history of breast cancer but no BRCA mutations to better characterize the CBC risk for these women.

They found that the long term CBC risk was significantly higher in women with hereditary breast cancer compared to the risk of developing a primary breast cancer in the general population. The overall probability for these women was 5.5 percent at 5 years and up to 27.3 percent at 20 years compared to only 1.9 percent at 5 years and 4.9 percent at 20 years for the general population. Further analysis by age group showed clearly that the 15 year probability of developing a CBC was significantly elevated for women under 50 years old compared to women over 50 years old (40 percent and 10 percent, respectively).

Women who took adjuvant hormonal therapy had significantly lowered risk for a CBC compared to those who did not take it. Adjuvant chemotherapy had no apparent effect on risk.

In the first published study to characterize CBC risk in non-BRCA hereditary breast cancers, the authors demonstrate “that women with hereditary/familial non-BRCA1/BRCA2 breast cancer have a very high risk of developing CBC.” The impact of these results is most apparent for premenopausal women, in who 1 in 5 will develop CBC after only 10 years. Consequently, conclude the authors, “it is important to consider and provide information about the risk of CBC.”

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