More than a dozen genes are linked to breast cancer risk, ranging from high-risk mutations that dramatically increase lifetime odds to moderate-risk variants that nudge risk modestly above average. The two most well-known, BRCA1 and BRCA2, account for the largest share of hereditary breast cancers, but they’re far from the full picture. Understanding which genes matter, and how much each one changes your risk, can shape decisions about screening, prevention, and family planning.
BRCA1 and BRCA2: The Highest-Risk Genes
BRCA1 and BRCA2 are tumor suppressor genes. They produce proteins that help repair damaged DNA in your cells. When either gene carries a harmful mutation, that repair process breaks down, and cells are more likely to grow out of control. More than 60% of women who inherit a harmful change in BRCA1 or BRCA2 will develop breast cancer during their lifetime, compared to about 13% of women in the general population.
The risk isn’t limited to breast cancer. Women with BRCA1 mutations face a 39% to 58% lifetime risk of ovarian cancer, while BRCA2 carriers face a 13% to 29% risk. Men can carry these mutations too. BRCA2 is the gene most strongly tied to male breast cancer, which is rare overall but significantly more common in male carriers.
BRCA mutations are inherited in an autosomal dominant pattern, meaning you only need one copy from one parent to have elevated risk. They’re found across all ethnic groups but are more common in certain populations, including people of Ashkenazi Jewish descent.
PALB2: A Risk Nearly as High as BRCA
PALB2 (partner and localizer of BRCA2) works closely with BRCA2 to repair DNA. For years it was considered a moderate-risk gene, but newer data tells a different story. The predicted average breast cancer risk by age 80 for a PALB2 mutation carrier is about 50%, which puts it in a similar category to BRCA1 and BRCA2, where average risk reaches around 74% by the same age. Many guidelines now treat PALB2 carriers similarly to BRCA carriers when it comes to screening and prevention recommendations.
ATM and CHEK2: Moderate but Meaningful
ATM and CHEK2 are the most commonly discussed moderate-penetrance genes. Both play roles in detecting and responding to DNA damage. The average breast cancer risk by age 80 is about 28% for ATM carriers and 30% for CHEK2 carriers. That’s roughly two to three times the general population risk.
These numbers represent averages. Your individual risk as a carrier depends on other factors: family history, breast density, reproductive history, and increasingly, your polygenic risk score (more on that below). Some ATM or CHEK2 carriers will have a risk profile close to the general population, while others will fall into a high-risk category that warrants more intensive screening.
CHEK2 mutations are particularly common in people of Northern and Eastern European descent. ATM mutations are best known for causing a rare childhood condition called ataxia-telangiectasia when both copies are affected, but carrying just one mutated copy raises breast cancer risk without causing that syndrome.
BARD1, RAD51C, and RAD51D
These three genes have gained attention more recently. All three help repair DNA through a process called homologous recombination, the same pathway that BRCA1 and BRCA2 support. Estimated lifetime breast cancer risks are 24% for BARD1 carriers, 22% for RAD51C carriers, and 21% for RAD51D carriers. That puts them in the moderate-risk category alongside ATM and CHEK2.
One notable feature of all three genes: carriers tend to develop estrogen-receptor-negative and triple-negative breast cancers at higher rates than the general population. This matters because triple-negative breast cancer is harder to treat and tends to be more aggressive. The connection is especially relevant for younger carriers, where the proportion of these harder-to-treat subtypes is highest.
RAD51C and RAD51D also carry elevated ovarian cancer risk, making them important to identify even though breast cancer risk alone is moderate.
Rare Syndrome-Associated Genes
Several genes raise breast cancer risk as part of broader genetic syndromes. Mutations in these genes are extremely rare in the general breast cancer population, but for individuals and families who carry them, the implications are significant.
- TP53 causes Li-Fraumeni syndrome, which raises the risk of many cancer types starting in childhood. Breast cancer is one of the most common cancers in women with this syndrome, often appearing before age 30. In population studies of breast cancer cases, TP53 mutations are found in roughly 1 in 1,800 patients.
- PTEN causes Cowden syndrome, marked by noncancerous growths and elevated risks of breast, thyroid, and uterine cancers. It’s found in about 1 in 3,750 breast cancer cases.
- CDH1 is most strongly associated with hereditary diffuse gastric cancer but also raises the risk of a specific type of breast cancer called lobular breast cancer. It appears in about 1 in 2,700 breast cancer cases.
- STK11 causes Peutz-Jeghers syndrome, which involves intestinal polyps and moderately elevated breast cancer risk. It’s the rarest of this group, found in roughly 1 in 11,500 breast cancer cases.
Because these mutations are so uncommon, genetic testing for them is typically guided by personal or family history suggesting one of these syndromes, rather than routine breast cancer screening panels.
Triple-Negative Breast Cancer and Genetics
Triple-negative breast cancer (TNBC) lacks the three most common receptors that drive breast cancer growth, which limits treatment options. BRCA1 is the gene most strongly linked to this subtype. Women with BRCA1 mutations develop triple-negative tumors at far higher rates than the general breast cancer population.
BARD1, RAD51C, and RAD51D carriers also develop triple-negative breast cancer more often than expected. The connection between DNA repair gene defects and this aggressive subtype has practical treatment implications: tumors with these underlying genetic features often respond well to a class of drugs called PARP inhibitors, which exploit the cancer cell’s inability to repair its own DNA.
Polygenic Risk: Beyond Single Genes
Most breast cancer is not caused by a single high-impact gene mutation. Instead, hundreds of common genetic variants, each contributing a tiny amount of risk, combine to shift your overall odds. A polygenic risk score (PRS) adds up the effects of these variants into a single number.
Polygenic risk scores work synergistically with single-gene results and traditional risk factors like family history, breast density, and age at first period. A CHEK2 carrier with a high polygenic risk score, for example, may have a risk profile that looks more like a BRCA carrier’s. A BARD1 carrier with a low score might fall close to population-level risk. In one analysis, about a third of BARD1 carriers were reclassified from moderate risk down to near-population risk when polygenic scores were factored in, while about 22% were reclassified upward to high risk.
Polygenic risk scores are increasingly available through genetic testing companies and some clinical programs. They’re most useful as a refinement tool, helping to personalize risk estimates that would otherwise rely on averages.
Screening for High-Risk Gene Carriers
If you carry a BRCA1 or BRCA2 mutation, both the American Cancer Society and the National Comprehensive Cancer Network recommend annual mammograms plus annual breast MRI starting at age 30. The NCCN recommends breast MRI alone from ages 25 to 29, with mammograms added at 30. Many providers stagger the two tests six months apart so you’re being screened every six months rather than getting both tests at once.
If you haven’t been tested yourself but have a first-degree relative (parent, sibling, or child) with a known BRCA mutation, enhanced screening is still recommended, typically starting at age 40 or 10 years before the youngest breast cancer diagnosis in your family, whichever comes first.
For carriers of moderate-risk genes like ATM, CHEK2, and PALB2, screening recommendations vary and are increasingly personalized based on the full risk picture, including family history and polygenic risk scores.
Preventive Options for High-Risk Carriers
Bilateral preventive mastectomy reduces breast cancer risk by at least 95% in women with BRCA1 or BRCA2 mutations and up to 90% in women with strong family histories. It’s the most effective risk-reduction strategy available, but it’s a major decision with permanent physical and emotional consequences.
Preventive removal of the ovaries and fallopian tubes is standard practice for BRCA carriers to reduce ovarian cancer risk. Some studies have suggested it also lowers breast cancer risk, though the evidence on that specific benefit is mixed. Risk-reducing medications, including drugs that block estrogen’s effects on breast tissue, are another option that can lower risk by roughly 30% to 50% depending on the drug and the population studied.
For carriers of moderate-risk genes, the decision calculus is different. Preventive surgery is less commonly recommended unless family history or other factors push overall risk into the high category. Enhanced screening and medication-based risk reduction are more typical starting points.