Breast cancer is inherited through specific gene mutations passed from parent to child in what’s called an autosomal dominant pattern. This means a parent who carries a harmful mutation in a breast cancer risk gene has a 50 percent chance of passing it to each child, regardless of the child’s sex. That said, inherited mutations account for only about 5% to 10% of all breast cancer cases. The vast majority arise from genetic changes that accumulate over a person’s lifetime rather than ones they were born with.
How the Inheritance Pattern Works
Everyone inherits two copies of every gene, one from each parent. The genes most strongly linked to hereditary breast cancer, BRCA1 and BRCA2, produce proteins that help repair damaged DNA. When one copy carries a harmful mutation, the second normal copy is usually enough to keep cells functioning properly. But over time, the working copy can become damaged or lost, which removes that safety net and allows cancer to develop.
This is why inheriting a mutation doesn’t guarantee cancer. It means you start life with only one functional copy instead of two, so there’s less margin for error as your cells divide over decades. The pattern is dominant because a single mutated copy is enough to raise risk significantly, even though both copies must ultimately fail for a tumor to form.
BRCA1 and BRCA2: The Highest-Risk Genes
BRCA1 and BRCA2 mutations carry the most significant breast cancer risk of any known inherited variants. Women with a BRCA1 mutation face a lifetime breast cancer risk of roughly 55% to 72%, while BRCA2 carriers face about 45% to 69%. For comparison, the average woman’s lifetime risk is about 13%.
These mutations also raise the risk of ovarian and fallopian tube cancer, pancreatic cancer, and in the case of BRCA2, prostate cancer in men. This cluster of risks is sometimes referred to as hereditary breast and ovarian cancer syndrome. Men who carry BRCA mutations can develop breast cancer too, though at much lower rates, and they pass the mutation to their children at the same 50% rate as women. A father who carries a BRCA mutation can pass it to sons or daughters equally.
Other Genes That Raise Risk
BRCA1 and BRCA2 get the most attention, but several other genes contribute to hereditary breast cancer. They vary in how much they increase risk.
PALB2 is the most notable. Women carrying a harmful PALB2 mutation have up to a 55% lifetime risk of breast cancer, putting it in a similar range to BRCA2. Men with PALB2 mutations have up to a 10% lifetime risk. The gene also raises the risk of ovarian cancer (up to 5%) and pancreatic cancer (up to 5%).
Other genes like CHEK2, ATM, and CDH1 carry moderate increases in risk. TP53 mutations cause Li-Fraumeni syndrome, a rare condition that dramatically raises the risk of multiple cancers including breast cancer, often at young ages. Each of these follows the same basic inheritance pattern: one mutated copy from one parent gives a 50% chance of passing it on.
What Family Patterns Suggest Inherited Risk
Certain patterns in a family tree raise the likelihood that a hereditary mutation is at play rather than coincidence. These include multiple relatives on the same side of the family diagnosed with breast cancer, breast cancer diagnosed before age 50, a family member with cancer in both breasts, ovarian cancer in the family, male breast cancer, or a relative with both breast and ovarian cancer. Ashkenazi Jewish ancestry also carries a higher prevalence of specific BRCA mutations.
It’s worth noting that the mutation can come through your father’s side just as easily as your mother’s. Because men with BRCA mutations rarely develop breast cancer themselves, the mutation can silently pass through generations of men before appearing in a woman who develops the disease. A family with no obvious history of breast cancer on the father’s side can still carry a high-risk mutation.
How Genetic Testing Works
Genetic testing for hereditary breast cancer typically involves a blood or saliva sample analyzed for mutations in known risk genes. The approach has shifted in recent years. Older tests focused specifically on BRCA1 and BRCA2, but multigene panel tests that screen dozens of genes at once are now standard. Research from Stanford Medicine found that multigene panels are about twice as likely as BRCA-only tests to identify a disease-associated mutation. They also provide information relevant to other family members who may be unknowing carriers.
Panel testing has trade-offs. It’s more likely to find variants of uncertain significance, meaning a genetic change was detected but scientists don’t yet know whether it actually raises cancer risk. This happens more frequently in people from racial or ethnic minority groups, whose genetic data is underrepresented in research databases. Interpreting panel results also requires genetic counseling expertise that isn’t always immediately available, and panel testing ordered after a cancer diagnosis is sometimes delayed until after surgery, which can limit treatment decisions.
What Carriers Can Do to Reduce Risk
Knowing you carry a mutation opens the door to several risk-reduction strategies. Enhanced screening is the most common starting point. This typically means breast MRIs alternating with mammograms every six months, beginning at a younger age than standard screening guidelines recommend.
For those who want more aggressive prevention, bilateral preventive mastectomy reduces breast cancer risk by at least 95% in women with BRCA1 or BRCA2 mutations. Preventive removal of the ovaries and fallopian tubes is also an option for those at high ovarian cancer risk, and it further reduces breast cancer risk when done before menopause. These are significant decisions that depend on a person’s age, family plans, and individual risk profile.
Preventing Transmission to Children
For carriers who want biological children without passing on the mutation, preimplantation genetic testing is an option. This involves IVF: embryos are created through fertilization outside the body, and each embryo is tested for the specific family mutation before being transferred. Only embryos without the mutation are implanted.
The process is more complex than standard IVF. It requires custom test development for each family’s specific mutation, which can take weeks to months. Genetic counseling is part of the process, and the testing is available for most single-gene conditions, including BRCA1 and BRCA2 mutations. It’s not guaranteed to work in every situation, and it adds cost and time to an already demanding fertility process, but it gives carriers the option of having children who won’t face the same elevated risk.