Genetics significantly affects about 5% to 10% of breast cancers. Having a sister or mother with breast cancer roughly doubles your risk, but most people who get breast cancer don’t have a close relative with it.
This article discusses the role of genetics in breast cancer, key genes, testing, and nongenetic risk factors.
Gene Mutations: A Risk for Breast Cancer
Genes are made from DNA (deoxyribonucleic acid), the heritable information you get from your parents. Inheriting certain (mutated) versions of specific genes, such as the BRCA1 gene (breast cancer susceptibility 1 gene), may increase your risk of breast cancer.
High-Penetrance Genes
High-penetrance genes increase your risk of breast cancer more than other types of genes. People with these genes are more likely to get cancer earlier than those with nongenetic breast cancer. They are also more likely to have cancer in both breasts and to have other cancers, such as ovarian cancer.
BRCA Genes
BRCA1 and BRCA2 genes are among the most important in assessing breast cancer risk. Females carrying one of these genes have a 50% to 85% chance of getting breast cancer in their lifetime. Additionally, they have a 10% to 40% risk of ovarian cancer and an elevated risk of other cancers. Men with BRCA mutations might be more likely to have prostate or pancreatic cancer.
You can inherit a mutated BRCA gene from either parent, and having only one BRCA gene still significantly increases your risk. While having a BRCA mutation gives you a genetic predisposition for breast cancer, it does not mean you will certainly get it.
Other Moderate to High-Penetrant Genes
Scientists have studied other, less common genes thought to increase cancer risk, but much less so than BRCA genes.
Many other genes also occur as part of broader medical conditions. They might increase your risk of breast cancer and multiple other medical problems, including different types of cancer. Some of these genes are:
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Low-Penetrance Genes
Low-penetrance genes have less of an impact on breast cancer risk than high-penetrance genes. Some of these genes may only increase risk if you’ve received a mutated version from both your parents rather than one, while others may only increase risk when triggered by environmental factors in a specific way.
These genes are not a standard part of genetic testing. Scientists are still researching these genes. It’s believed that more low-penetrance genes are yet to be identified based on the number of family-linked breast cancer cases. However, it could also be due to other shared risk factors within a family.
Assessing Genetic Risk
Having a family history of breast cancer increases your risk, but the specifics of this can vary.
For example, a history of breast cancer in a parent or full sibling (first-degree relatives) increases your risk more than breast cancer in further-removed relatives such as a cousin, aunt, or grandmother.
Not surprisingly, having two first-degree relatives with breast cancer increases your risk even more. Having one first-degree relative with breast cancer doubles your risk, while having two almost triples it.
Family History That Increases Your Genetic Risk
Having family members with the following history might also put you at an increased risk for breast cancer:
Breast cancer at a younger age (under 45) Multiple family members with breast cancer Breast cancer in a male relative Breast cancer occurring in both breasts Breast cancer occurring with other cancers (e. g. , ovarian)
Other Risk Factors
Factors other than genetics and family history that may influence your breast cancer risk include:
Being female (identified as female at birth) Increased age Extended reproductive history (starting menses (first period) before age 12 or menopause after age 55 ) Having dense breasts Other breast diseases (e. g. , fibroadenoma) Never being pregnant, having a first pregnancy after age 30, or not breastfeeding Using certain forms of hormonal contraceptives (e. g. , certain types of birth control pills) Receiving hormone replacement therapy after menopause
Certain lifestyle choices can also affect your risk for breast cancer, including increased alcohol consumption, smoking, and lack of physical activity (especially after menopause). You may be able to prevent additional breast cancer risk by limiting or abstaining from alcohol and tobacco and staying active.
Breast Cancer Genetic Tests
Genetic testing is an important part of assessing breast cancer risk. These tests often look for the BRCA1 or BRCA2 mutations, but other genes might be tested in certain circumstances.
Testing is typically recommended for those predisposed to a BRCA1 or BRCA2 mutation. Your healthcare provider may suggest testing if:
Someone in your family has tested positive for one of the BRCA mutations. Your medical history or your family history of breast cancer is more consistent with BRCA-related cancer (e. g. , breast cancer before age 45, cancers in the ovary or fallopian tube, or cancer in more than one breast). You have breast cancer in your family and are of Ashkenazi Jewish descent.
Summary
About 5% to 10% of breast cancer is genetic, often from the inheritance of a BRCA mutated gene. While the BRCA mutation puts you at a genetic predisposition and increases your risk for breast cancer, it doesn’t mean you will get it.
Your medical history, family history, and lifestyle factors play a role in breast cancer risk. If you’re concerned about your risk for breast cancer, speak to your healthcare provider about genetic testing, most likely for the BRCA gene.
A Word From Verywell
If someone in your family has had breast cancer, it’s only natural to wonder about your own risk. Unfortunately, clear-cut answers aren’t always available. Speak with your healthcare provider about your questions and concerns. Together, you can decide on the best ways to manage your risk.
