37.6 percent of women in the study experienced a new cancer in the untreated breast.

Results from a prospective study are published in the January 1, 2005, issue of CANCER, a peer-reviewed journal of the American Cancer Society.

Conflicting Data

Breast conserving therapy (BCT), consisting of lumpectomy and radiation, has been demonstrated to be a safe, effective treatment for non-hereditary or sporadic forms of early breast cancer.

However, for hereditary breast cancers -- i.e., mutations in BRCA1 and BRCA2 genes -- the use of BCT is controversial due to conflicting data about increased risk of recurrence in the treated breast and development of new tumors in the untreated breast.

This leaves women with BRCA mutations at a disadvantage when choosing between BCT and bilateral mastectomy.

Mark Robson, M.D., and his colleagues from Memorial Sloan-Kettering Cancer Center in New York City followed 87 women diagnosed with breast cancer and BRCA mutations who were treated with BCT to evaluate their long-term cancer risks.

Untreated Breast More Vulnerable

The investigators found no increase in the risk of cancer recurrence in the treated breast, compared to young women without mutations. Ten years after their initial diagnosis, 13.6 percent of the women with a genetic mutation had experienced a recurrence similar to previously published recurrence rates for women with non-hereditary breast cancers treated with BCT.

However, the researchers note that more than half the women suffered a cancer-related event (recurrence or second primary cancer) within ten years of their initial diagnosis, including 37.6 percent who experienced a new cancer in the untreated breast. No clinical risk factors were linked to an increased risk of cancer.

"Breast conserving treatment," conclude the authors, "is a reasonable option for [women with BRCA mutations], and the indications for unilateral mastectomy should be the same for both hereditary and non-hereditary breast cancer." They caution, however, "discussion of bilateral mastectomy is warranted by the significant contralateral breast cancer risk."