Obviously, contralateral prophylactic mastectomy (CPM)-removal of the noncancerous breast-reduces the risk of contralateral breast cancer, yet little evidence exists regarding its effect on life expectancy. Nevertheless, more American women with breast cancer are electing to undergo the procedure than ever before. Authors of a recent study suggest this may be attributable to women's overestimation of both their risk of developing contralateral breast cancer-a tumor in the opposite breast diagnosed more than six months after the first tumor-and the efficacy of CPM. To help women and their physicians make more informed decisions, the authors developed a statistical probability algorithm to predict the impact of CPM on 20-year survival outcomes in women with unilateral stage I or II breast cancer but without a BRCA mutation. They used public cancer databases and registries to form patient cohorts based on age, estrogen-receptor status (positive or negative), and cancer stage (I or II).

They found that in women who underwent CPM, the lower the cancer stage, the greater the life expectancy-an extension of as long as seven months in 40-year-olds and of less than two months in 60-year-olds. Women with estrogen receptor-negative breast cancer did slightly better with CPM than their positive counterparts. Both of these findings, the authors suggest, mirror baseline risk probabilities in these groups: the life expectancy of older women is generally shorter than that of younger women; stage I breast cancer has a better prognosis, generally, than stage II; and estrogen receptor-negative breast cancer confers a higher risk of contralateral breast cancer development than does estrogen receptor-positive cancer. The authors admit that the results may reflect a selection bias-women who underwent CPM tend to be younger, white, have a higher education level, and have private insurance-but also say this suggests that the impact of CPM may be even lower than their research shows.

The most important takeaway, the one that should help inform decisions about CPM, is that none of the groups, regardless of age, estrogen receptor status, or breast cancer stage "had a greater than 1% absolute [increase in] survival at 20 years."-Sibyl Shalo Wilmont, BSN, RN

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