Some cancers are inherited, but most are not
Cancer is not usually genetic in the way you might think. About 5 to 10 percent of cancers are caused by inherited gene mutations—changes in DNA that run through families. The other 90 to 95 percent develop because of things that happen during a person's lifetime: smoking, sun exposure, infections, age, or random cellular damage that accumulates over time.
The confusion comes from the word "genetic." People often use it to mean "runs in families," but that is not what geneticists mean. A genetic mutation is a change in your DNA code. An inherited mutation is one you were born with, passed down from a parent. Most cancers are genetic in the sense that they involve mutations—but those mutations happened in the cancer cells themselves, not in your body from birth.
If cancer runs in your family, that does not automatically mean you inherited a cancer-causing mutation. It can mean your relatives were exposed to the same risk factors (like smoking in the same household), or it can be coincidence. Families are small groups, and cancer is common, so clusters happen by chance.
Key Takeaways
- Only 5 to 10 percent of cancers are caused by inherited mutations; the rest develop from exposures and aging.
- Having a family history of cancer does not mean you inherited a mutation or that you will definitely get cancer.
- Specific patterns—like cancer before age 50, multiple relatives with cancer, or certain cancer types—suggest inherited mutations are more likely.
- Genetic testing can tell you whether you carry a mutation, but only a doctor or genetic counselor can interpret what it means for your health.
- Knowing your family history is the first step; talking to your doctor about it is how you figure out what to do next.
Which cancers are more likely to be inherited
Certain cancers show up in families more often than others. Breast cancer, ovarian cancer, and colon cancer are the most common inherited forms. Pancreatic cancer, melanoma, and stomach cancer can also run in families, though less frequently.
The genes most often involved are called BRCA1 and BRCA2. If you inherit a mutation in one of these genes, your risk of breast cancer rises to 45 to 87 percent by age 80, depending on which gene and which mutation. Your risk of ovarian cancer also rises. Other inherited mutations affect genes like MLH1, MSH2, and MSH6, which increase colon cancer risk.
But even if you carry one of these mutations, cancer is not certain. A mutation raises your risk, sometimes dramatically, but it does not may provide you will get sick. Some people with BRCA mutations never develop cancer. Others do. The difference depends on other genes you carry, your environment, your choices, and chance.
Red flags that suggest inherited mutations might be in your family
Certain patterns make inherited mutations more likely. If cancer showed up in your family before age 50, that is a flag—most cancers happen later in life, so early onset suggests a genetic cause. If multiple relatives on the same side of the family had cancer, especially the same type, that is another sign. If a relative had two different cancers, or if a man in your family had breast cancer, those are strong indicators.
Ancestry also matters. People of Ashkenazi Jewish descent have higher rates of BRCA mutations. Certain populations have higher rates of other inherited mutations. If you know your family came from a region where genetic testing has identified common mutations, that information is worth mentioning to your doctor.
If none of these patterns fit your family, inherited mutations are still possible but less likely. The absence of a clear pattern does not rule them out—it just means the odds are lower.
How genetic testing works and what it can tell you
Genetic testing involves a blood or saliva sample sent to a lab. The lab looks for known mutations in specific genes. The test can come back three ways: positive (you carry a mutation), negative (you do not carry the mutations tested for), or uncertain (the lab found something but does not know what it means yet).
A positive result means you have a mutation that raises your cancer risk. It does not mean you have cancer or will definitely get it. A negative result is more reassuring but not absolute—there are mutations scientists have not yet identified, and the test only looks for known ones. An uncertain result is frustrating; it usually means the lab needs more information or more people to study before they can say whether the mutation matters.
Testing is not something you do on your own. You need a doctor or genetic counselor to order it, explain what it means, and help you decide what to do with the information. Genetic counselors are specially trained to discuss family history, explain test results, and talk through the emotional and practical weight of knowing you carry a mutation. Many insurance plans cover genetic counseling if your doctor refers you.
What to do if you have a family history of cancer
Start by talking to your doctor about your family history. Write down what you know: which relatives had cancer, what type, and how old they were. If you do not know details, ask other family members. The more specific you are, the better your doctor can assess your risk.
Your doctor may refer you to a genetic counselor or a cancer specialist. They may recommend more frequent screening (like earlier or more often mammograms if breast cancer runs in your family), or they may suggest genetic testing. They may also discuss ways to lower your risk through lifestyle changes or, in some cases, preventive surgery or medication.
If genetic testing is recommended and you decide to do it, understand that the result affects not just you but potentially your relatives. Some people find that information valuable; others find it burdensome. It is okay to take time deciding whether testing is right for you.
The difference between risk and destiny
Carrying a mutation that raises cancer risk is not the same as having a death sentence. People with inherited mutations live long, healthy lives. Some get cancer; many do not. The mutation is one piece of a much larger picture that includes your other genes, your environment, your health habits, and random chance.
Knowing you carry a mutation can actually be useful. It lets you make informed choices: whether to screen more often, whether to take preventive medication, whether to have preventive surgery, or whether to focus on modifiable risk factors like not smoking or limiting alcohol. It also means your relatives can make informed choices about their own testing and screening.
The goal of understanding your genetic risk is not to live in fear. It is to know what you are dealing with so you can make decisions that fit your values and your life.
Frequently Asked Questions
If my mother had breast cancer, will I definitely get it?
No. Even if your mother had breast cancer, you may never develop it. If she had an inherited mutation, your risk is higher than average, but most women with inherited mutations do not get cancer. Your actual risk depends on which gene is involved, your other genes, your lifestyle, and chance. A genetic counselor can give you a more specific estimate based on your family details.
Can I get genetic testing without a family history of cancer?
Yes, though it is less common. Some people get tested because they had cancer themselves at a young age, or because they belong to a population with higher mutation rates. Your doctor can discuss whether testing makes sense for your situation. Testing is not routine for people with no personal or family history of cancer.
If I test negative for a mutation, does that mean I will not get cancer?
No. A negative test means you do not carry the specific mutations the test looked for, which lowers your risk compared to someone with a mutation. But it does not eliminate your risk. Most cancers are not caused by inherited mutations, so you still have the same baseline risk as anyone else from age, environment, and lifestyle factors.
Should I tell my family if I have a genetic mutation?
That is your choice, but many people do tell relatives because the information can help them make decisions about their own screening and testing. Some families find it helpful; others find it stressful. A genetic counselor can help you think through how and when to share the information.
Does having a genetic mutation mean I should have preventive surgery?
Not necessarily. Preventive surgery (like removing breasts or ovaries before cancer develops) is one option some people with mutations choose, but it is not the only option. Others choose frequent screening, preventive medication, or lifestyle changes. The right choice depends on your risk level, your values, your age, and your personal circumstances. This is a decision to make with your doctor.