Bilateral Mastectomy Lowers Risk of Contralateral Breast Cancer But Not Mortality

Women with unilateral breast cancer (BC) treated with bilateral mastectomy have a significantly reduced risk of contralateral BC (CBC) compared with unilateral mastectomy or lumpectomy, but not mortality, according to researchers from Women’s College Hospital in Toronto. Their findings challenge the existing belief that bilateral mastectomy provides a survival advantage for women with unilateral BC.

While bilateral mastectomy significantly reduces the risk of CBC, it does not improve overall survival compared with lumpectomy or unilateral mastectomy. Image Credit: © Gorodenkoff - stock.adobe.com

BC survivors have an increased risk of developing second breast, contralateral, and other cancers, emphasizing the necessity for continued monitoring and risk reduction to prevent onset of disease. CBC accounts for approximately 0.5% of women with breast cancer per year, with mutation status, race and ethnicity, age, and menopausal status significantly influencing risk.¹

Prior studies have supported the benefit of bilateral mastectomy for treatment of unilateral BC but lacked distinct analysis of the effect on mortality. The researchers conducted a cohort study of 661,270 women (mean [SD] age, 58.7 [11.3] years) with stage 0 to stage 3 unilateral BC to investigate the 20-year cumulative risk of BC mortality. The Surveillance, Epidemiology, and End Results Program registry database to identify women with unilateral BC who were diagnosed from 2000 to 2019. The participants were divided into 3 equally sized cohorts (n= 36,028) based on the surgery type, which included lumpectomy, unilateral mastectomy, or bilateral mastectomy. The data were analyzed from October 2023 to February 2024.^2,3

According to their observations, once diagnosed with CBC, a patient’s risk of mortality increases 4-fold and prevention through preemptive surgery may not reduce risk of mortality over time. At the 20-year follow-up, there were 766, 728, and 97 CBC diagnoses in the lumpectomy, unilateral mastectomy, and bilateral mastectomy cohorts, respectively. Additionally, the risk of developing CBC was 6.9% (95% CI, 6.1%-7.9%) in the lumpectomy-unilateral mastectomy group.^2,3

The cumulative mortality rate across the 3 cohorts was 32.1% at 15 years after developing a contralateral cancer and was 14.5% for those who did not develop a contralateral cancer (hazard ratio, 4.00; 95% CI, 3.52-4.54, using contralateral breast cancer as a time-dependent covariate). The researchers observed no significant difference in overall mortality across the cohorts. Deaths from BC amounted to 8.54% of women in the lumpectomy group, 9.07% in the unilateral mastectomy group, and 8.50% in the bilateral mastectomy group. Further, after CBC diagnosis, mortality rates were 3.89% (95% CI 3.36-4.49) in the first 5 years, 4.12% (95% CI 3.24-5.23) in 5 to 10 years, and 4.48% (95% CI 2.73-7.35) in 10 to 15 years.^2,3

While bilateral mastectomy significantly reduces the risk of CBC, it does not improve overall survival compared with lumpectomy or unilateral mastectomy. This challenges the longstanding belief that aggressive surgical intervention translates to better long-term outcomes. The findings underscore a crucial shift in understanding the benefits of bilateral mastectomy and emphasize the importance of continued monitoring and personalized risk assessment for breast cancer survivors.

References

1. Yadav S, Boddicker N, Na J, et al. Contralateral breast cancer risk among carriers of germline pathogenic variant in atm, brca1, brca2, chek2, and palb2. J Clin Oncol. January 9, 2023. doi:10.1200/JCO.22.01239

2. Giannakeas V, Lim DW, Narod SA. Bilateral mastectomy and breast cancer mortality. JAMA Oncol. July 25, 2024. doi:10.1001/jamaoncol.2024.2212

3. Bilateral mastectomy reduces contralateral breast cancer risk, but not mortality. MedPage Today. July 29, 2024. Accessed July 31, 2024. https://www.medpagetoday.com/hematologyoncology/breastcancer/111287#:~:text=Across%20the%20three%20groups%2C%20there,lumpectomy%20and%20bilateral%20mastectomy%20groups