Family History and Genetic Testing for Cancer: When to Test

The headline number is smaller than most people expect. NCI puts it at about 5% to 10% of all cancers. Those are the ones thought to come from a harmful gene change inherited from a parent.

That leaves a lot of cancer that clusters in families for other reasons. NCI names one directly. A shared setting or habit, such as tobacco use, can cause similar cancers in relatives. No inherited gene change is needed.

So the question is not whether cancer appears twice in a family tree. It is whether the pattern fits.

NCI lists specific features that raise the possibility of a hereditary cancer syndrome:

• A family member with a known inherited harmful gene change.
• Cancer diagnosed at a young age, for example colon cancer before age 50.
• Several different types of cancer in the same person.
• Cancer in several family members, especially several first-degree relatives with the same type. A first-degree relative is a parent, sibling, or child.
• Breast and ovarian cancer appearing in the same family.
• Colon and endometrial cancer appearing in the same family.
• Cancer in both organs of a pair, such as both breasts or both kidneys.
• A rare cancer type, such as male breast cancer.
• Birth defects known to go with inherited cancer syndromes.
• Membership in a racial or ethnic group with known raised risk of a particular syndrome, together with one or more of the features above.

Notice that several of these are about combinations, not counts. Breast plus ovarian in one family means more than four relatives with unrelated cancers. The same goes for colon plus endometrial.

Some diagnoses trigger testing on their own. NCI states that clinical practice guidelines recommend genetic testing for anyone diagnosed with:

• Triple-negative breast cancer.
• Ovarian cancer.
• Pancreatic cancer.
• Colorectal cancer before age 50.
• Metastatic prostate cancer.
• Male breast cancer.

The reason is practical, not about family trees. For these cancers, an inherited change can point to the best treatment. It also matters for blood relatives.

This is the point most often missed, and it saves money and confusion.

NCI's guidance is clear. When possible, counseling and testing should begin with a family member who has had cancer.

The logic is simple. Say a relative with cancer tests negative. Testing a healthy relative then adds little. Now say that relative tests positive. Everyone else can be tested for that one change. That is faster and cheaper than a broad panel.

A genetic counselor, doctor, or other provider usually orders the test. They do that after reviewing personal and family medical history and spotting a possible pattern.

The sample is small. It is usually blood. Sometimes it is saliva, cells from inside the cheek, or skin cells. It goes to a genetic testing laboratory. Results usually come back in about 2 to 3 weeks.

On cost, NCI is specific. Health insurance typically covers counseling and tests judged medically necessary. People without insurance can find affordable testing through subsidized programs. NCI's Cancer Information Service can help locate them. Settle costs and coverage with the provider and the insurer before testing.

The standard approach now uses multigene tests, also called panel tests. They check many genes at once. They are used when no gene change is already known in a family.

Then comes a choice. One option is a focused panel, aimed at genes tied to one cancer type. The other is a broad panel, covering genes linked to many common cancers. NCI says the choice depends on personal and family history. It also depends on how much information a person wants.

When a variant is already known in the family, testing narrows. Sometimes the whole gene is read. Sometimes only the one known variant is checked.

There are more than two possible answers, and the differences matter.

Positive. The lab found a change tied to higher cancer risk. Such changes are called pathogenic or likely pathogenic variants. For someone with cancer, this may explain the diagnosis and guide treatment. For future risk, NCI lists what it can change. Screening can start younger or happen more often. Medicines or surgery can lower risk. Habits such as smoking can be addressed. And it can guide decisions about fertility and pregnancy.

True negative. A specific variant was known in the family, and this person did not inherit it. Risk is probably about the same as the general population.

Uninformative negative. The family history is strong, but no harmful change was found in anyone. An undetected variant may still exist. NCI notes that some people here may still benefit from more frequent checkups.

Variant of uncertain significance. There is not enough data to classify the change. Most are later reclassified as harmless. So a VUS is typically not used for health decisions. Stay in contact with the testing provider, because classifications do change.

Genetic makeup does not change, so a specific test rarely needs repeating. NCI names the exceptions:

• After an uninformative negative, since new genes are discovered regularly and technology improves.
• Occasionally on a second tissue type, such as a skin biopsy, to confirm an inconclusive blood or saliva result.
• When a new cancer or clinical feature appears that suggests a different syndrome.

Testing for inherited cancer risk is not the same as tumor testing. Tumor genetic testing, also called tumor DNA sequencing, somatic testing, or biomarker testing, looks for changes that happened during a person's lifetime in the cancer itself.

Tumor testing can sometimes pick up an inherited change. But NCI is clear that it does not replace testing for inherited risk. So watch for one mix-up. If a tumor panel report is being used to answer a family question, say so.

For related reading, see our overview of cancer prevention and our page on early-onset cancer in young adults.

• National Cancer Institute, Genetic Testing for Inherited Cancer Risk, accessed August 6, 2026
• National Cancer Institute, BRCA Gene Changes: Cancer Risk and Genetic Testing, accessed August 6, 2026