Why Does Bilateral Mastectomy Not Further Reduce Breast Cancer Mortality?
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Why Does Bilateral Mastectomy Not Further Reduce Breast Cancer Mortality?
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Why Does Bilateral Mastectomy Not Further Reduce Breast Cancer Mortality?
Recent statistics indicate that in 2022, there were over 2.3 million new cases of breast cancer among women globally, with more than 660,000 deaths attributed to the disease .
For many newly diagnosed breast cancer patients, the most significant decision during treatment is the choice of surgical procedure. Increasingly, women diagnosed with unilateral breast cancer opt for bilateral mastectomy due to concerns about developing new tumors in the opposite breast, especially among younger patients.
Extensive research has confirmed that bilateral mastectomy significantly reduces the risk of developing cancer in the opposite breast. However, there is no evidence to suggest that this procedure further reduces breast cancer mortality. Despite this, many patients choose bilateral mastectomy in the hope that it will decrease breast cancer-related deaths.
Recently, a study led by Steven Narod’s research team from the University of Toronto, published in the prestigious medical journal JAMA Oncology , may provide reassurance for breast cancer patients considering breast-conserving surgery or unilateral mastectomy.
Narod’s team analyzed over 100,000 breast cancer patients with follow-up data spanning 20 years. They found that although patients who underwent bilateral mastectomy had a significantly lower risk of developing cancer in the opposite breast compared to those who had breast-conserving surgery or unilateral mastectomy, the 20-year cumulative mortality risk was similar across all three surgical groups.
In summary, compared to breast-conserving surgery or unilateral mastectomy, bilateral mastectomy does not further reduce the mortality risk for breast cancer patients.
This study, the largest and longest follow-up of its kind to date, sheds light on this critical issue.
Over the past two decades, the use of bilateral mastectomy has increased. However, its potential to offer more significant survival benefits remains unproven.
Although contralateral breast cancer is the most common secondary primary cancer among breast cancer patients, its incidence is very low. Previous studies may not have observed survival benefits from bilateral mastectomy due to small sample sizes.
To determine the true value of bilateral mastectomy, Narod’s team accessed the SEER (Surveillance, Epidemiology, and End Results) database from the U.S. National Cancer Institute. They extracted data for 661,270 women aged 30 to 80 who were diagnosed with unilateral in situ or invasive breast cancer between 2000 and 2019.
The researchers matched 36,028 breast cancer patients for each surgical procedure (breast-conserving surgery, unilateral mastectomy, and bilateral mastectomy), resulting in a total of 108,084 patients. The groups were similar in demographics, clinical variables, treatment variables, and propensity scores.
Specifically, in the breast-conserving surgery group, 766 patients developed contralateral invasive breast cancer, with a 20-year cumulative incidence of 7.8%. In the unilateral mastectomy group, 728 patients developed contralateral invasive breast cancer, with a 20-year cumulative incidence of 6.1%. In the bilateral mastectomy group, only 97 patients developed contralateral invasive breast cancer, with a 20-year cumulative incidence of 0.7%. This indicates that the risk of developing contralateral invasive breast cancer is indeed very low for breast cancer patients, but the risk reduction in the bilateral mastectomy group was significant—an 88% reduction.
The 20-year cumulative mortality rates were as follows: 16.3% in the breast-conserving surgery group (3,077 deaths), 16.7% in the unilateral mastectomy group (3,269 deaths), and 16.7% in the bilateral mastectomy group (3,062 deaths). This shows no significant difference in long-term mortality among the three groups.
Notably, Narod’s team also provided another set of data. Among patients who developed contralateral breast cancer, the 15-year cumulative breast cancer mortality rate was 32.1%, compared to 14.5% for those who did not develop contralateral breast cancer. This suggests that patients with contralateral breast cancer have a 300% increased risk of dying from breast cancer compared to those without it (HR=4).
This finding contradicts the previous belief that contralateral breast cancer, usually detected early, does not impact survival. It also challenges the notion that bilateral mastectomy reduces mortality since, theoretically, preventing the occurrence of contralateral breast cancer should prevent deaths. Why, then, do the data show no reduction in mortality?
Narod suggests that the issue lies in the spread of the primary breast cancer to other parts of the body, and the occurrence of contralateral breast cancer may distract from this more critical concern. In other words, while worrying about contralateral breast cancer, it is the silent spread of the primary tumor that needs attention.
Based on these findings, Steven Narod and his colleagues believe that clinicians should inform women with unilateral breast cancer that although bilateral mastectomy significantly reduces the risk of contralateral breast cancer, it does not impact long-term mortality.
Current consensus and guidelines do not recommend bilateral mastectomy for patients with average risk. This large-scale study may help women understand that there is no difference in survival rates between breast-conserving surgery, unilateral mastectomy, and bilateral mastectomy.
Why Does Bilateral Mastectomy Not Further Reduce Breast Cancer Mortality?
References:
- Bray F, Laversanne M, Sung H, et al. Global cancer statistics 2022: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin. 2024;74(3):229-263. doi:10.3322/caac.21834
- Giannakeas V, Lim DW, Narod SA. Bilateral Mastectomy and Breast Cancer Mortality. JAMA Oncol. Published online July 25, 2024. doi:10.1001/jamaoncol.2024.2212
(source:internet, reference only)
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