If a patient is diagnosed with breast cancer, that patient’s risk of developing cancer in the other breast (which doctors refer to as contralateral breast cancer) may increase 3-4 times. The risk of contralateral breast cancer is different from the risk of recurrence of the primary breast cancer. This risk is also higher than the risk of first-time breast cancer in the average woman.
A study from the Netherlands showed that if a patient carries the abnormal BRCA1 or BRCA2 gene and has been diagnosed with breast cancer, the patient’s risk of developing contralateral breast cancer is 16-40%, about 3-6 times higher than women who do not carry the abnormal BRCA1 or BRCA2 gene. The study was published in the Journal of Clinical Oncology on December 23, 2015.
Physicians would like to have a more accurate contralateral breast cancer risk assessment for women diagnosed with breast cancer who carry the abnormal BRCA1 or BRCA2 gene; this assessment would help physicians develop appropriate screening and treatment plans based on each patient’s individual circumstances and respective contralateral breast cancer risk.
This study has already found that women who carry the abnormal BRCA1 or BRCA2 gene and are first diagnosed with breast cancer before the age of 41 have twice the risk of contralateral breast cancer than those who are first diagnosed with breast cancer between the ages of 41 and 49.
The Dutch have a universal health care system, so all researchers had access to information on every case of women diagnosed with breast cancer.
In this study, the researchers identified 6,294 women with invasive breast cancer diagnosed at age ≤49 years. These women were treated from 1970-2003. The researchers also tested tissue or blood samples from these patients to clarify whether the patients carried the abnormal BRCA1 or BRCA2 gene. The results found that 3.2 percent of the patients carried the abnormal BRCA1 gene (200 women) and 1.1 percent carried the abnormal BRCA2 gene (71 women). The researchers did not indicate how many women carried both of these abnormal genes.
Gene mutation status and risk of contralateral breast cancer
After approximately 12.5 years of follow-up, 578 contralateral breast cancers were diagnosed.
521 contralateral breast cancers occurred in women who did not carry the abnormal gene
45 contralateral breast cancers occurred in women carrying the abnormal BRCA1 gene
12 contralateral breast cancers occurred in women with the abnormal BRCA2 gene
The risk of patients being diagnosed with contralateral breast cancer 10 years after the first breast cancer diagnosis were
5.1% risk for women who did not carry the abnormal gene
21.1% risk for women carrying the abnormal BRCA1 gene
10.8% for women carrying the abnormal BRCA2 gene
The risk of contralateral breast cancer differed significantly between women carrying the abnormal BRCA1 or BRCA2 gene and those not carrying the abnormal gene. In other words, contralateral breast cancer may arise not only as an incidental event but also due to abnormal genes.
Age at first breast cancer diagnosis and risk of contralateral breast cancer
The researchers then examined the effect of age at first diagnosis of breast cancer on the risk of contralateral breast cancer in women carrying the abnormal BRCA1 or BRCA2 genes.
Ten years after the first diagnosis of breast cancer, the risk of contralateral breast cancer was diagnosed as follows, respectively
23.9% risk for women aged ≤41 years at first diagnosis
Risk for women aged 41-49 years at first diagnosis was 12.6%
In women who do not carry the abnormal gene, there is no increased risk of contralateral breast cancer in patients with age at first diagnosis <41 years.
Screening and treatment strategies
If a patient has been diagnosed with breast cancer and is clearly carrying the abnormal BRCA1 or BRCA2 gene themselves, the patient and the patient’s physician need to carefully consider the patient’s risk of developing a new cancer and patient preferences when developing a treatment plan. This study provides more detailed information for patients to assess their risk.
Depending on the patient’s risk, patients may choose more aggressive measures to make the risk as low as possible, such as
Hormone therapy to block the effects of estrogen on breast tissue or to lower the body’s estrogen levels
Surgical removal of the contralateral breast and/or ovary (prophylactic mastectomy and/or prophylactic oophorectomy)
Patients can also reduce their risk by making lifestyle changes, such as avoiding alcohol and tobacco, maintaining a healthy weight and exercising regularly.
Each case is unique for each woman. Overall, patients and their physicians can assess the patient’s risk and find the best way to manage it.