Most inherited cases of breast cancer are associated with one of two abnormal genes: BRCA1 (BReast CAncer gene one) or BRCA2 (BReast CAncer gene two).
Everyone has BRCA1 and BRCA2 genes. The function of the BRCA genes is to repair cell damage and keep breast cells growing normally. But when these genes contain abnormalities or mutations that are passed from generation to generation, the genes don't function normally and breast cancer risk increases. Abnormal BRCA1 and BRCA2 genes may account for up to 10% of all breast cancers, or 1 out of every 10 cases.
Women with a BRCA1 or BRCA2 genetic mutation:
- have up to a 72% lifetime risk of developing breast cancer
- have a much higher-than-average lifetime risk of ovarian cancer; estimates range from 17% to 44%
- have a much higher-than-average risk of developing a new, second breast cancer after an initial diagnosis
A small Canadian study suggests that women with an abnormal BRCA1 or BRCA2 gene who develop breast cancer in one breast are 50% more likely to survive breast cancer if they have a double mastectomy (have both breasts removed).
The study was published online on Feb. 11, 2014 by the British Medical Journal. Read “Contralateral mastectomy and survival after breast cancer in carriers of BRCA1 and BRCA2 mutations: retrospective analysis.”
This study was a retrospective study, which means the researchers analyzed information that was collected before the study was designed. The results of retrospective studies aren’t considered as strong as results from studies that are designed first and then collect new information specifically for that study.
The researchers looked at the medical records of 390 women with an abnormal BRCA1 or BRCA2 gene who were diagnosed with stage I or stage II breast cancer. The women were first treated with either a single or double mastectomy. Overall, 181 women had a double mastectomy and 209 had single mastectomy. The women were followed for 20 years after they were diagnosed. The researchers found:
- women who had a double mastectomy were 48% more likely to survive breast cancer compared to women who had a single mastectomy
- women who had a single mastectomy and developed breast cancer in the other breast were twice as likely to die from breast cancer
- 20 years after diagnosis, survival rates were 88% for women who had a double mastectomy and 66% for women who had a single mastectomy
While these results suggest that having both breasts removed is the best option for women who have an abnormal BRCA1 or BRCA2 gene and are diagnosed with early stage breast cancer, the study does have some weaknesses:
- The study was small -- the records of only 390 women were analyzed.
- The study wasn’t randomized; this means that the women weren’t randomly assigned to have either single mastectomy or double mastectomy. It could be that other factors also affected survival rates.
If you have an abnormal BRCA1 or BRCA2 gene and have been diagnosed with breast cancer, you and your doctor will carefully consider your risk of developing a new cancer as well as your preferences as you develop your treatment plan. Choosing to have the opposite healthy breast removed is one option you may consider. You also may consider having your ovaries preventively removed. Taking tamoxifen, a type of hormonal therapy medicine, is another option. There are also lifestyle steps you can take, including maintaining a healthy weight, avoiding alcohol, and exercising regularly.
Each woman’s situation is unique. Talk to your doctor about your level of risk and ways to manage it that are best for you.
For more information on steps you can take to reduce your risk of being diagnosed with a first or second breast cancer if you have an abnormal BRCA1 or BRCA2 gene, visit the Genetics page in the Breastcancer.org Lower Your Risk section.
Editor’s Note: This article was updated on Jan. 24, 2019, with updated information on cancer risk associated with BRCA mutations.