Some cancers are hereditary, but most are not—and having a family history does not mean you will get cancer

About 5 to 10 percent of cancers are hereditary, meaning they result from an inherited gene mutation passed down through a family. The remaining 90 to 95 percent develop from a combination of age, lifestyle, and random cellular changes that happen during a person's lifetime. If multiple relatives have had cancer, or if someone was diagnosed young, hereditary cancer is more likely—but family history alone does not determine your risk. Understanding the difference between inherited mutations and sporadic cancer helps you know whether genetic testing makes sense for your situation.

Key Takeaways

  • Hereditary cancers account for only 5 to 10 percent of all cancers and result from specific gene mutations inherited from a parent.
  • Having a family member with cancer does not automatically mean you inherited a cancer-causing mutation or that you will develop cancer.
  • Certain patterns—multiple relatives with cancer, diagnosis before age 50, or specific cancer types like ovarian or pancreatic—suggest hereditary cancer may be present in your family.
  • Genetic testing can identify inherited mutations, but only a genetic counselor or doctor can determine whether testing is appropriate for you based on your family history.
  • Knowing your hereditary risk allows you to pursue screening, prevention, and surveillance strategies that may reduce your cancer risk.

How hereditary cancer differs from sporadic cancer

Hereditary cancer results from a germline mutation—a change in DNA that a person inherits from a parent and carries in every cell of their body from birth. If you inherit a hereditary cancer mutation, you have a significantly higher lifetime risk of developing that cancer, though inheritance does not may provide you will develop it. Common hereditary cancer genes include BRCA1 and BRCA2 (linked to breast, ovarian, and pancreatic cancers), Lynch syndrome genes (linked to colorectal and endometrial cancers), and RB1 (linked to retinoblastoma).

Sporadic cancer, which accounts for the vast majority of cases, develops when mutations accumulate in cells over time due to aging, sun exposure, smoking, alcohol use, or random chance. These mutations are not inherited and cannot be passed to children. A person can have a family member with sporadic cancer and have no increased risk themselves.

Red flags that suggest hereditary cancer in your family

Certain patterns in a family's cancer history raise the likelihood that a hereditary mutation is present. These include cancer diagnosed before age 50, multiple relatives with the same or related cancers (such as breast and ovarian cancer), cancer in both breasts, male breast cancer, or specific cancer types like ovarian, pancreatic, or gastric cancer that are less common overall but more common in hereditary syndromes. Ashkenazi Jewish ancestry also increases the likelihood of carrying BRCA1 or BRCA2 mutations.

However, even one of these patterns does not confirm hereditary cancer. A single early diagnosis could be coincidence. Multiple relatives with cancer could reflect shared lifestyle factors—smoking, for example—rather than a shared mutation. A genetic counselor reviews your full family history to assess whether the pattern suggests hereditary cancer or is more consistent with sporadic cases.

How genetic testing works and who should consider it

Genetic testing involves a blood or saliva sample that a laboratory analyzes for known cancer-causing mutations. The test itself is straightforward, but deciding whether to test requires careful thought. Testing is most useful when your family history suggests a hereditary mutation is present—not when you simply want to know your cancer risk in general. Testing a family member who has had cancer is often more informative than testing someone who has not, because a positive result in that person confirms the mutation exists in your family.

A genetic counselor—a healthcare professional trained in hereditary cancer—helps you understand your family history, explains what a positive or negative result would mean for you, and discusses the emotional and practical implications. Some people find that knowing their status helps them make informed decisions about screening and prevention. Others find the uncertainty of a negative result (which does not rule out all hereditary cancer risk) or the burden of a positive result difficult to manage. Genetic counseling before testing helps you decide whether testing aligns with your values and circumstances.

What a positive genetic test result means for your health

If you test positive for a hereditary cancer mutation, it means you carry that mutation in your cells and have an elevated lifetime risk of developing certain cancers. The exact risk depends on which gene is mutated. For example, women who carry a BRCA1 mutation have roughly a 45 to 87 percent lifetime risk of breast cancer and a 17 to 44 percent risk of ovarian cancer, depending on the specific mutation and other factors. These are significantly higher than the general population risk, but they are not certainties.

A positive result opens options for managing your risk: more frequent screening (such as MRI in addition to mammography for breast cancer), preventive surgery (such as prophylactic mastectomy or oophorectomy), chemoprevention with medications like tamoxifen, and lifestyle changes. Your doctor can discuss which strategies fit your situation. A positive result also means your blood relatives may carry the same mutation, and some may want to pursue testing themselves.

What a negative genetic test result means

A negative result means you did not inherit the specific mutation the test looked for. However, a negative result does not eliminate your cancer risk. You still have the same baseline cancer risk as anyone in the general population, which increases with age. Additionally, if your family history strongly suggests hereditary cancer but testing is negative, a mutation may exist that current tests do not detect, or the cancer in your family may result from a combination of common genetic variants and lifestyle factors rather than a single inherited mutation.

A negative result is most reassuring when a close relative with cancer tested positive for a mutation and you tested negative—that result means you did not inherit that particular mutation. If no one in your family has tested positive, a negative result in you is less conclusive about whether hereditary cancer is present in your family.

Lifestyle and screening strategies regardless of hereditary risk

Whether or not you have a family history of cancer, certain behaviors reduce cancer risk across the board. These include not smoking, limiting alcohol, maintaining a healthy weight, exercising regularly, eating a diet rich in vegetables and whole grains, protecting your skin from sun exposure, and staying up to date with recommended cancer screenings (mammography, colonoscopy, cervical cancer screening). For people with a known hereditary cancer mutation, these steps become even more important because they address the portion of cancer risk that is not genetic.

If you have a family history of cancer but have not pursued genetic testing, screening recommendations may still change based on your family history alone. For example, someone with a mother and sister who had breast cancer before age 50 might begin mammography earlier than standard guidelines recommend, even without genetic testing. Your doctor can discuss what screening makes sense for your specific situation.

Frequently Asked Questions

If my parent had cancer, will I definitely get cancer?

No. Even if your parent had hereditary cancer and passed a mutation to you, inheriting the mutation does not may provide you will develop cancer. Penetrance—the likelihood that someone with a mutation will develop cancer—varies by gene and by individual. Some people with hereditary cancer mutations never develop cancer in their lifetime. Lifestyle factors, other genetic variations, and chance all play a role.

Can I have hereditary cancer without any family history?

Yes, though it is less common. A hereditary mutation can appear in a family for the first time if a parent developed a new mutation that was not inherited from their parents. Additionally, if relatives with cancer are unknown or estranged, you may not know your full family history. Genetic testing can reveal hereditary mutations even when family history seems unremarkable.

Does a negative genetic test mean I will not get cancer?

No. A negative test means you did not inherit the specific mutation tested for, but everyone has some baseline cancer risk that increases with age. You still need to follow general cancer prevention strategies and recommended screenings. If your family history is very suggestive of hereditary cancer, a negative result may mean a mutation exists that the test did not detect.

How much does genetic testing cost?

Cost varies widely depending on which genes are tested, whether insurance covers it, and which laboratory performs the test. Many insurance plans cover genetic testing when a doctor orders it based on family history, though you may have a copay or coinsurance. Some laboratories offer testing at reduced cost or free if you meet certain criteria. Ask your doctor or genetic counselor about cost before proceeding.

Should I tell my relatives if I test positive for a hereditary cancer mutation?

That is a personal decision. A positive result means your blood relatives may carry the same mutation and could benefit from knowing that information. However, sharing genetic information is sensitive, and some relatives may not want to know. A genetic counselor can help you think through how and whether to share this information with family members.