*For medical professionals only
According to the latest statistics, in 2022, there were more than 2.3 million new cases of breast cancer and more than 660,000 deaths in women worldwide [1].
For many newly diagnosed breast cancer patients, the biggest issue they face during treatment is the choice of surgery. Due to concerns about the growth of new tumors in the opposite breast, more and more people with unilateral breast cancer are opting for bilateral mastectomy, especially younger patients.
Bilateral mastectomy has been shown to significantly reduce the risk of contralateral breast cancer, but there is no evidence that bilateral mastectomy further reduces breast cancer mortality. Despite this, many patients opt for bilateral mastectomy in the hope that it will reduce breast cancer-related mortality.
Recently, a research team led by Steven Narod of the University of Toronto, Canada, published a blockbuster research result in the top medical journal JAMA Oncology [2], which may allow breast cancer patients to choose breast-conserving surgery or unilateral mastectomy with peace of mind.
Narod's team analyzed 20-year follow-up data from more than 100,000 breast cancer patients and found that those who underwent breast-conserving surgery or unilateral mastectomy had a significantly lower risk of developing contralateral breast cancer than those who underwent breast-conserving surgery or unilateral mastectomy, but there was no difference in the cumulative 20-year risk of death between the three procedures.
In simple terms, bilateral mastectomy did not further reduce the risk of death in breast cancer patients compared to breast-conserving surgery or unilateral mastectomy.
It is understood that this is also the largest and longest follow-up study to date.
▲ Screenshot of the Home of the paper
Bilateral mastectomy has been increasingly used in the last 20 years, but the jury is still out on whether this procedure will provide additional survival benefits.
Although contralateral breast cancer is the most common second primary cancer of primary breast cancer, the incidence of contralateral breast cancer is low. Therefore, previous studies did not observe a greater survival benefit with bilateral mastectomy, which may be related to the small sample size.
To determine the true value of bilateral mastectomy, the Narod team found the United States National Cancer Institute's surveillance, epidemiology, and final results (SEER) database, from which they extracted 661,270 women aged 30 to 80 years who were diagnosed with unilateral orthotopic or invasive breast cancer between 2000 and 2019.
Subsequently, they matched 36,028 breast cancer patients to breast-conserving surgery, unilateral mastectomy, and bilateral mastectomy from all patients in a 1:1:1 ratio, for a total of 108084 patients. The groups were similar in demographic, clinical, treatment variables, and propensity scores.
Specifically, 766 patients in the breast-conserving group developed contralateral invasive breast cancer, with a cumulative incidence of 7.8% in 20 years; In the unilateral mastectomy group, 728 patients developed contralateral invasive breast cancer, with a cumulative incidence of 6.1% in 20 years. Contralateral invasive breast cancer occurred in 97 patients in the bilateral mastectomy group, with a cumulative 20-year incidence of 0.7%. It is not difficult to see that the risk of developing contralateral invasive breast cancer in breast cancer patients is actually very low; However, patients in the bilateral mastectomy group did have an 88% lower risk of developing contralateral invasive breast cancer.
The number of deaths from breast cancer in each group was as follows: 3077 in the breast-conserving group, with a cumulative incidence rate of 16.3% in 20 years; There were 3269 patients in the unilateral mastectomy group, with a cumulative incidence rate of 16.7% in 20 years. There were 3062 patients in the bilateral mastectomy group, with a cumulative incidence rate of 16.7% in 20 years. That is, there was no significant difference between the three groups in terms of long-term mortality.
▲ 20-year cumulative morbidity and mortality
It is worth noting that the Narod team also provided another set of data. In the breast-conserving and unilateral mastectomy groups, the 15-year cumulative breast cancer mortality was 32.1% for those who developed contralateral breast cancer and 14.5% for those who did not develop contralateral breast cancer. This also means that patients who develop contralateral breast cancer have a 300% increased risk of dying from breast cancer compared to those who do not develop contralateral breast cancer (HR=4).
This finding is inconsistent with the previous belief that contralateral breast cancer is generally detected earlier and does not affect survival. Moreover, this conclusion is contrary to the fact that bilateral mastectomy does not reduce mortality, after all, bilateral mastectomy can reduce the risk of contralateral breast cancer, and theoretically, preventing it can prevent death. So why does the data show that it has not decreased?
Narod believes that it is the primary breast cancer that metastasizes to other parts of the world, and we are so confused by the occurrence of contralateral breast cancer that we forget the impact of metastasis of the primary lesion elsewhere. To put it simply, when we are worried about contralateral breast cancer, it is the cancer cells that quietly spread to other parts of the country that need to be worried, and the lethality of contralateral breast cancer is questionable.
Based on these findings, Steven Narod and his colleagues believe that clinicians should inform women with unilateral breast cancer that bilateral mastectomy, while significantly reducing the risk of developing contralateral breast cancer, does not affect long-term mortality.
In fact, current consensus and guidelines do not recommend bilateral mastectomy for average-risk patients. Hopefully, this large-scale study will help women in general understand that there is no difference in survival between breast-conserving surgery, bilateral mastectomy, and bilateral mastectomy.
Bibliography:
[1]. 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
[2]. 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
本文作者丨BioTalker