Understanding the Genes That Influence Breast Cancer Risk

If you have a family history of breast cancer, you may wonder how much of your risk is inherited. Modern genetic research provides clear answers.

Scientists have identified mutations in two genes—BRCA1 and BRCA2—as the primary hereditary drivers of breast cancer. While not every breast‑cancer case is genetic, carrying a harmful mutation in either gene markedly raises a woman’s lifetime risk.

Below we explain how these mutations work, who should consider genetic testing, and what other hereditary genes may be involved.

How Gene Mutations Lead to Cancer

Genes encode proteins that regulate cell growth and repair DNA damage. When a mutation disrupts this function, cells can grow abnormally and eventually become cancerous. Some mutations are inherited (present at birth), while others arise later due to environmental factors.

Current estimates suggest that 5–10 % of breast cancers are hereditary.

BRCA1 and BRCA2: The Core Breast‑Cancer Genes

Both BRCA1 and BRCA2 produce proteins that help fix DNA breaks, especially in breast and ovarian tissue. A harmful mutation impairs this repair mechanism, allowing atypical cells to proliferate.

According to the Centers for Disease Control and Prevention (CDC), roughly 50 % of women who inherit a BRCA mutation will develop breast cancer by age 70.

Individuals with these mutations also face elevated risks for other cancers, such as ovarian, pancreatic, prostate, and, in men, male breast cancer.

Who is More Likely to Carry a BRCA Mutation?

• Multiple close relatives with breast cancer
• Breast cancer diagnosed before age 50 in a family member
• Any family history of ovarian cancer
• A male relative with breast cancer
• Families with both breast and ovarian cancers
• Known BRCA mutation in the family

Other Hereditary Breast‑Cancer Genes

Beyond BRCA1/2, several additional genes can increase risk when mutated:

• CHEK2: 20–40 % lifetime breast‑cancer risk; also linked to colorectal cancer and male breast cancer.
• CDH1: Raises risk of lobular breast cancer and hereditary diffuse gastric cancer.
• PALB2: Partners with BRCA proteins; carriers face a 40–60 % lifetime risk versus 12.5 % in the general population.
• PTEN: Causes Cowden syndrome, which predisposes to benign and malignant breast tumors.
• TP53: Leads to Li‑Fraumeni syndrome, a condition associated with breast, brain, and other cancers.

Genetic Testing: What to Expect

If you meet any of the risk criteria above, genetic testing may be advisable. Testing for BRCA1/2 typically involves a simple blood draw or saliva sample sent to a certified laboratory. Results are interpreted by a genetic counselor or physician.

Direct‑to‑consumer kits usually screen only for BRCA1/2 and cannot assess the full spectrum of hereditary risk.

The National Comprehensive Cancer Network (NCCN) outlines specific guidelines for who should be offered testing. Insurance coverage varies, and testing is not routinely recommended for the general population.

When Testing Is Recommended

• A known BRCA1 or BRCA2 mutation in the family
• Strong family history of breast or ovarian cancer
• Moderate family history plus Ashkenazi Jewish or Eastern European ancestry
• Personal history of ovarian, fallopian‑tube, or peritoneal cancer
• Diagnosis of certain high‑risk breast‑cancer subtypes

Testing is generally not advised for children under 18, as preventive options are limited at that age.

Key Takeaways

• Everyone carries BRCA1 and BRCA2; only mutations raise cancer risk.
• A mutation does not guarantee cancer, but it does increase probability.
• Understanding your genetic risk can guide surveillance and risk‑reduction strategies.

If you have a family history of breast cancer, discuss the benefits and limitations of genetic testing with a qualified healthcare professional.