What Is Genetic Testing for Cancer?

Genetic tests can determine whether you are at risk of developing cancer by identifying mutations in a person’s genes. The risk of developing cancer increases if you have a genetic predisposition or susceptibility to cancer. Approximately 5% to 10% of all cancers are related to an inherited gene mutation. Finding a mutation may help provide an early diagnosis and peace of mind. However, genetic testing can't detect all gene mutations, may provide false negative results, and can result in increased anxiety and high medical costs.

Inherited vs. Acquired Mutations

Most cancers start because of acquired gene mutations that happen during a person’s lifetime. Sometimes these gene changes have an outside cause, such as exposure to sunlight or tobacco, but gene mutations can also be random events that happen inside a cell without a clear reason.

Acquired mutations only affect cells that grow from the mutated cell. They do not affect all the cells in a person’s body. All the cancer cells will have the mutations, but normal cells in the body will not. Because of this, these mutations are not passed on to a person’s children. This is very different from inherited mutations, which are in every cell in the body, including the cells without cancer.  

oral DNA swab

Peter Dazeley / Getty Images

What Is a Genetic Predisposition to Cancer?

Genetic predisposition is an increased chance of developing cancer due to gene mutations in specific genes. These variations are frequently inherited from a parent. While inheriting these genetic mutations increases the risk of cancer, it doesn’t mean someone with inherited gene mutations will necessarily develop cancer. In other words, cancer is not inherited, but someone can inherit a gene that increases their risk of cancer. That predisposition can be large or small, depending on the particular gene and other risk factors.

What Are Genetic Tests for Cancer?

Two types of tests are used to identify a genetic predisposition:

  • Germline testing - when normal cells in the body (such as blood or cells from a cheek swab) are tested for genetic mutations that may be inherited and increase the risk of cancer
  • Somatic tumor testing - when cells from a known cancer are tested for mutations that may affect prognosis or determine treatment

Multifactorial Disorders

Researchers are learning that almost all diseases have a genetic element, including cancer. Some conditions are caused by mutations in a gene like cystic fibrosis and sickle cell disease. However, some diseases like heart disease or type 2 diabetes are likely caused by changes in multiple genes combined with lifestyle and environmental conditions. Conditions caused by many contributing factors are called multifactorial or complex disorders.

Although multifactorial disorders are normally found in families, it’s difficult to pinpoint a clear pattern of inheritance, which makes it hard to assess the risk of inheriting the condition.

Should I Get Tested?

If you are concerned about your family’s medical history related to cancer, you may want to consult a genetic counselor and get tested.

You may want to get genetic testing for cancer predisposition if you have any of the following:

  • Several first-degree relatives (mother, father, sisters, brothers, children) with cancer
  • Many relatives on one side of the family who have had the same type of cancer
  • A cluster of cancers in your family that are known to be linked to a single gene mutation (such as breast, ovarian, and pancreatic cancers)
  • A family member with more than one type of cancer 
  • Family members who had cancer under age 50
  • Close relatives with cancers that are linked to rare hereditary cancer syndromes
  • A family member with a rare cancer, such as breast cancer in a man
  • Ashkenazi Jewish ancestry
  • A physical finding that’s linked to an inherited cancer, such as having many colon polyps
  • A known genetic mutation in one or more family members who have already had genetic testing

Genetic testing cannot determine the risk of all types of cancers.

The Downside of Genetic Testing

Getting screened for cancer can help, but there is no question that it comes with some stressors, including: 

  • Limited answers: Testing doesn’t provide a definitive answer whether you will get cancer. It only tells you that you have a gene mutation. A negative result also doesn’t exclude the possibility of developing the disease
  • Family matters: Having to deal with the prospect that you may have inherited a cancer-related gene and other family members may have died from the disease or can have the mutation may make you feel guilty and angry
  • More testing: If a gene mutation is found for a specific cancer, more tests to follow up may be recommended. The added time and expense can lead to more stress
  • Costs: Genetic testing comes with a hefty price tag. You will also have to deal with your insurance company to learn whether they will pay for the screening
  • Privacy issues: Questions of how your information is used by medical and pharmaceutical researchers, insurers, and even employers can cause anxiety

Speak with a genetic testing counselor to discuss any of these concerns.

How Is Genetic Testing Done?

Prior to a genetic test, you'll meet with a genetic counselor, who will go through the procedure and answer any question you may have. They will talk about the testing procedure, as well as the test’s benefits, limitations, and the significance of your test results

A sampling of blood, hair, skin, amniotic fluid, or other tissues is taken and sent to a lab where technicians examine changes in DNA, chromosomes, and proteins. Results are sent in writing to your genetic counselor, doctor, or, if requested, directly to you.

Now you also have the option of conducting a genetic test at home.

Home Testing

The only cancer risk home test approved by the U.S. Food and Drug Administration (FDA) is the Genetic Health Risk Report for BRCA1/BRCA2 by the genetic testing company 23andMe. The test looks for three specific variations in the BRCA1 and BRCA2 genes that are associated with an increased risk of breast cancer, ovarian cancer, and potentially other forms of cancer in people of Ashkenazi (Eastern European) Jewish ancestry.

This test requires you to collect a saliva sample in a test tube. Afterwards, you will have to ship it to the lab. Test results are posted on a secure website for your review. The test can detect genetic markers that indicate increased risk of cancer, but that doesn’t necessarily mean that you will definitely develop cancer. 

More than 1,000 variations in each of the BRCA1 and BRCA2 genes have been associated with an increased risk of cancer. The FDA-approved direct-to-consumer genetic test analyzes only three of these variations, however. Also, the variations included in the test are much more common in people of Ashkenazi Jewish background than in people of other ethnicities, so the results may not be useful to you if you are of a different ethnic background.

The FDA warns that consumers and healthcare professionals should not use the test results to determine any treatments. Instead, these decisions require confirmatory testing and genetic counseling. 

Types of Tests Available

Genetic testing is available for the following types of cancers: 

  • Breast and ovarian cancer: Genetic tests look for mutations in the BRCA1 and BRCA2 genes. Your doctor may recommend other tests using a multigene panel that examines mutations in several genes. If you are of Ashkenazi Jewish or Eastern European ancestry, your doctor may recommend other tests for three specific BRCA1 and BRCA2 mutations, called founder mutations
  • Colon cancer: Colorectal cancer, in some instances, can be caused by Lynch syndrome, or hereditary nonpolyposis colorectal cancer (HNPCC). Approximately 3% of colorectal cancer cases are caused by Lynch syndrome. If you have been diagnosed with Lynch syndrome, you’re more likely to develop colorectal cancer, especially at a young age. Women diagnosed with Lynch syndrome are more likely to get endometrial (uterine) cancer and ovarian cancer. Both men and women with Lynch syndrome are at higher risk for stomach, liver, kidney, brain, and skin cancer.
  • Thyroid cancer: There’s a genomic test available that assesses 112 genes linked to thyroid cancer. The test looks at mutations, gene fusions, changes in copy number, and gene expression
  • Prostate cancer: About 5% to 10% of prostate cancers are hereditary. The BRCA1 and BRACA2 genes are also associated with prostate cancer. Other mutated genes that can cause prostate cancer, including HOXB13, ATM, and genes known as DNA mismatch repair genes, which are linked to Lynch syndrome 
  • Pancreatic cancer: About 3% to 5% of pancreatic cancers are caused by inherited genetic syndromes, while 5% to 10% are familial pancreatic cancer (a family history of the disease). However, a specific mutation that increases the risk for cancer has not been identified. If you have family members with Peutz-Jeghers syndrome, an inherited cancer predisposition disorder associated with the STK11 gene that can lead to gastrointestinal polyps and skin freckling, you are at an increased risk of other cancers.
  • Melanoma: A small number of melanomas are inherited, but some families have high rates of the disorder with mutations in the CDKN2A gene
  • Sarcoma: Many inherited cancer syndromes that are linked to the development of sarcoma appear in childhood with a mutation in the retinoblastoma (RB) gene RB1
  • Kidney cancer: Inherited DNA changes can cause kidney cancer such as a mutation in the VHL gene, which is a tumor suppressor gene. Other suppressor genes like the FH gene (associated with leiomyomas), the FLCN gene (Birt-Hogg-Dube Syndrome), and the SDHB and SDHD genes (familial renal cancer) may lead to an increased risk of kidney cancer
  • Stomach cancer: Nearly 1% to 3% of stomach cancers are caused by a CDH1 gene mutation. This mutation is an inherited cancer syndrome that can increase the risk of both stomach and lobular breast cancer. Individuals who inherit this gene mutation are at high risk of getting stomach cancer when they're young

What Do Test Results Mean?

Your genetic test results could be:

  • Positive: The laboratory found a genetic variant that is associated with an inherited cancer susceptibility syndrome. For a person who has cancer, this confirms that the cancer was likely due to an inherited genetic variant. This result also indicates that there is an increased risk of developing cancer in the future
  • Negative: The laboratory did not find the specific variant that the test was designed to detect. This result is most useful when a specific disease-causing variant is known to be present in a family. A negative result can show that the tested family member has not inherited the variant and that this person does not have inherited cancer susceptibility syndrome. This is called a true negative. It does not mean that there is no cancer risk, but that the risk is probably the same as the cancer risk in the general population
  • Variant of uncertain significance: The testing indicates a variant that hasn't been linked to cancer. Your doctor may interpret the result as uncertain. This result offers no certainty related to risk and is not taken into consideration when making a healthcare decision
  • Benign variant: This result indicates a genetic modification detected isn't unusual. Benign variants are not linked to an increased risk in cancer

A Word From Verywell

Genetic testing is an important tool that can give you peace of mind. For individuals who have a family history of cancer, it can also be a lifesaver and alert them to monitor any changes to their health so their cancers can be diagnosed and treated early. It's important to remember, though, that genetic tests for cancer cannot detect risk of all types of cancers.

If you plan to take a genetic test to determine if you have a higher risk of cancer, you should undergo genetic counseling so all your questions can be answered. Keep in mind that if your family is predisposed to cancer, that doesn’t necessarily mean you will develop the disease. 

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Cancer Society. Understanding genetic testing for cancer. Updated April 10, 2017.

  2. National Cancer Institute. Genetic testing fact sheet. Updated March 15, 2019.

  3. MedlinePlus Genetics. What are complex or multifactorial disorders? Updated September 18, 2020.

  4. American Cancer Society. Should I Get Genetic Testing for Cancer Risk? May 23, 2016.

  5. MedlinePlus Genetics. How is Genetic Testing Done? Updated September 18, 2020.

  6. MedlinePlus. Can a direct-to-consumer genetic test tell me whether I will develop cancer? Updated September 28, 2020.

  7. Harvard Health. Should you try a home genetic test kit? August 2017.

  8. U.S. Food and Drug Administration. FDA authorizes, with special controls, direct-to-consumer test that reports three mutations in the BRCA breast cancer genes. Published March 6, 2018.

  9. Centers for Disease Control and Prevention. Genetic Testing for Hereditary Breast and Ovarian Cancer. Updated June 10, 2019.

  10. American Cancer Society. Genetic testing, screening, and prevention for people with a strong family history of colorectal cancer. Updated June 29, 2020.

  11. National Cancer Institute. Genomic Test Helps Identify Thyroid Nodules That Don’t Require Surgery.  November 30, 2018.

  12. Urology Care Foundation. Genetic Testing for Prostate Cancer: What You Should Know. Fall 2018.

  13. Lab Tests Online. Screening for Pancreatic Cancer in People with Genetic Risk. Updated July 10, 2020.

  14. American Cancer Society. Genetic Counseling for People at High Risk of Melonoma. Updated August 14, 2019.

  15. American Cancer Society. What Causes Kidney Cancer? Updated February 1, 2020.

  16. Johns Hopkins Medicine. Hereditary Diffuse Gastric Cancer(HDGC).

  17. National Cancer Institute. Genetic Testing for Inherited Cancer Susceptibility Syndrome. Updated March 15, 2019.