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.

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

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.

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, healthcare provider, 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 healthcare provider 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 practitioner 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-Dubé 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 healthcare provider 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.