“The efficacy of prophylactic mastectomy in reducing the incidence of breast cancer is well established,” Dr. Isabelle Bedrosian and co-authors, from the M.D. Anderson Cancer Center, Houston, note. However, “the potential benefit of contralateral prophylactic mastectomy in reducing breast cancer mortality has not been adequately studied.”
To investigate, the researchers analyzed data from the Surveillance, Epidemiology, and End Results database on 107,106 women who had mastectomies between 1998 and 2003. This cohort included 8902 women who had the contralateral breast removed as well, according to the report in the February 25th online issue of the Journal of the National Cancer Institute.
On initial analysis, contralateral prophylactic mastectomy was associated with a 37% reduced risk of death from breast cancer (p < 0.001). Further investigation showed that this was driven by a reduction in breast cancer–specific mortality in the subset of 4854 women aged 18 to 49 years with stage I/II ER-negative cancer (hazard ratio, 0.69).
Without mastectomy of the other breast, 5-year adjusted breast cancer-specific survival was 83.7%; with contralateral mastectomy, the rate climbed slightly to 88.5%.
In the women with early stage disease who did have the second breast removed, rates of metachronous primary cancer in the contralateral breast did not differ significantly by ER status.
Without a contralateral prophylactic mastectomy, however, 44 of 4854 (0.90%) young women with ER-negative tumors developed a cancer in the second breast at a median follow-up of 47 months, compared to 53 of the 11,585 young women (0.46%) with ER-positive tumors (p < 0.001).
There was no indication that contralateral prophylactic mastectomy improved the survival of patients over 60 years of age, regardless of disease stage and ER status. “Breast cancer patients over the age of 60 can be reassured that they will not benefit from CPM,” Dr. Bedrosian said in a statement.
“However, there are other populations—such as women between the age of 50 and 60—where the findings about the procedure remain less clear,” she said. Similarly, the benefit of CPM for young women with early stage, ER-positive breast cancer who receive tamoxifen for only 5 years needs to be clarified.
J Natl Cancer Inst 2010.