From the Guidelines
The annual incidence of contralateral breast cancer is approximately 0.5-1% per year for women with a history of breast cancer. This risk is based on the most recent and highest quality study available, which reported that the risk for contralateral cancer is 0.5% to 1% per year during the 10 years after diagnosis 1. The risk varies based on several factors including age at first diagnosis, genetic predisposition, family history, and original tumor characteristics. For example, women diagnosed with breast cancer at a young age, particularly those with BRCA1 or BRCA2 mutations, have a higher risk of developing contralateral breast cancer.
Some key factors that influence the risk of contralateral breast cancer include:
- Age at first diagnosis: younger women have a higher risk
- Genetic predisposition: particularly BRCA1/2 mutation carriers who have a 2-3% annual risk
- Family history: women with a strong family history of breast cancer are at higher risk
- Original tumor characteristics: such as hormone receptor status and tumor grade
Hormonal therapies like tamoxifen and aromatase inhibitors can reduce the risk of contralateral breast cancer by approximately 50% in women with hormone receptor-positive disease 1. Regular surveillance with mammography of the contralateral breast is important for early detection, and some high-risk patients may benefit from MRI screening. Understanding this risk is important for breast cancer survivors' long-term follow-up care planning.
It's worth noting that the risk of contralateral breast cancer is cumulative over time, so after 10 years, approximately 5-10% of breast cancer survivors may develop contralateral breast cancer. However, with proper surveillance and risk reduction strategies, the risk of contralateral breast cancer can be minimized, and breast cancer survivors can reduce their risk of morbidity and mortality, and improve their quality of life.
From the FDA Drug Label
The proportional reductions in the incidence of contralateral breast cancer among women receiving tamoxifen were 13% (NS), 26% (2p = 0.004) and 47% (2p < 0.00001), with a significant trend favoring longer tamoxifen duration (2p = 0. 008). Treatment with about 5 years of tamoxifen reduced the annual incidence rate of contralateral breast cancer from 7.6 per 1,000 patients in the control group compared with 3. 9 per 1,000 patients in the tamoxifen group. In NSABP B-14, the annual rate of contralateral breast cancer was 8.0 per 1,000 patients in the placebo group compared with 5. 0 per 1,000 patients in the tamoxifen group, at 10 years after first randomization.
The annual incidence of contralateral breast cancer is:
- 7.6 per 1,000 patients in the control group
- 3.9 per 1,000 patients in the tamoxifen group (with 5 years of treatment)
- 8.0 per 1,000 patients in the placebo group
- 5.0 per 1,000 patients in the tamoxifen group (in the NSABP B-14 trial) 2
From the Research
Annual Incidence of Contralateral Breast Cancer
The annual incidence of contralateral breast cancer is a significant concern for women who have been diagnosed with unilateral breast cancer. Several studies have investigated this issue, providing valuable insights into the risk factors and incidence rates.
- The annual risk of contralateral breast cancer is approximately 0.5% on average, but it increases to 3% in carriers of BRCA1 or BRCA2 mutations 3.
- A study published in 2012 found that the risk of contralateral breast cancer is approximately 0.5% per year 4.
- Another study published in 2011 reported a decline in the incidence of contralateral breast cancer in the United States from 1975 to 2006, with an estimated annual percent change of -3.07% per year 5.
- A more recent study published in 2021 estimated that breast cancer patients have approximately twice the risk of developing cancer in the contralateral breast compared to the general population, with a standardized incidence ratio of 2.21 6.
- A study published in 2006 found that the annual risk of developing any contralateral breast cancer remained constant at approximately 0.75% per year after treatment with breast-conserving treatment and radiation 7.
Risk Factors for Contralateral Breast Cancer
Several risk factors have been identified for contralateral breast cancer, including:
- Young age at first diagnosis of breast cancer 3, 6
- Family history of breast cancer 3
- Carriers of BRCA1 or BRCA2 mutations 3
- Estrogen receptor status of the first breast cancer 5, 6
Detection and Surveillance
Regular surveillance is essential for detecting contralateral breast cancer, and mammography is a commonly used method for detection 4, 7. However, the sensitivity of mammography may be lower in younger women, and other imaging modalities may be necessary in this setting 4.