Genes are written in a genetic code that is made up of many, many DNA (deoxyribonucleic acid) “letters” which provide instructions that make you you. They determine your hair color, eye color, adult height, and many, many other things.
In some cases, though, genetic makeup can raise your risk of developing certain medical conditions such as cancer. Genes that are considered “cancer genes” are quite helpful and important because they help to prevent us from developing cancer. But, when someone has a spelling error, or a mutation, in one of those protective genes, it can lead to the development of cancer. If someone is born with one of those gene mutations because it is inherited from a parent, having that abnormal gene can increase that person’s chance to develop certain types of cancer. The cancer itself is not inherited, but the gene that increases the risk to develop the cancer is inherited.
Knowing whether you have a higher genetic chance to develop a certain type of cancer can arm you with information to protect your health.
Up to 1 in 10 Cancers Have Hereditary Causes
The American Cancer Society estimates nearly 1.9 million new cases of cancer will be diagnosed in 2022. About 5-10% of all cancers have a hereditary genetic component.
If you have a family history of cancer, your doctor or a genetic counselor may recommend you undergo genetic testing for hereditary cancer. This type of testing investigates some of your genes, looking for specific variants in those genes that might increase your risk of developing cancer. These variants, also called mutations, are referred to as cancer susceptibility variants. Inheriting one makes you more likely to develop specific types of cancer but inheriting the variant does not mean you will get cancer.
When Should Genetic Testing for Cancer Be Done?
Your doctor might recommend genetic counseling and testing if you:
- Have a strong family history of specific types of cancer. Genetic testing, in this instance, would be to determine whether you have inherited a genetic mutation that could increase your risk for certain types of cancers.
- Have been diagnosed with cancer. Genetic testing in someone who has cancer can be used to help guide the treatment process and is more likely to be recommended if you also have other factors, such as a family history of the same cancer or related cancers (like multiple people with breast cancer, or combination of breast and ovarian cancers), a diagnosis at a young age (like breast cancer at age 45 or younger), or a diagnosis of a rare type of cancer (like ovarian or pancreatic cancer).
- Have a known family history of a gene mutation. Genetic testing would help identify whether you have the gene mutation. The results can guide health care decisions that might reduce your risks.
How do doctors tell if you have a strong family history of cancer? They will look for certain factors in both your mother’s side of the family and your father’s side of the family, including whether you have:
- Multiple relatives with the same type of cancer
- Family members with a cluster of related cancers
- Family members with rare types of cancers
- A family member with multiple types of cancer
- A family member diagnosed with a specific cancer at a younger-than-normal age
Genetic testing is available for breast cancer, ovarian cancer, colorectal cancer, prostate cancer, melanoma, pancreatic cancer, kidney cancer, and many other types.
If You Choose Genetic Testing
If you decide to have genetic testing for cancer, there are two main types. Somatic testing is done on a sample of a tumor that has already been detected; this can help provide information to doctors on how to treat that tumor. In germline testing, a saliva or blood sample is analyzed to look for inherited mutations.
Depending on your personal and family histories, your doctor or a genetic counselor will help you decide what test is best for you. Most testing that is done is some form of multigene panel, which examines many genes at once. Testing panels can be focused on just genes related to breast cancer, or cast a wide net and look at genes related to multiple cancer types like breast, colon, ovarian, etc. Panels can test only genes with known management guidelines or can include genes that have a newer and less understood link to cancer. If there is a known gene mutation in the family history, then typically only site-specific or targeted testing is needed to look for just the specific family mutation. When you meet with a genetic counselor, he or she will take a detailed family history, discuss testing options, and review the different types of results that could come back, all to help you to come to the best testing decision for you.
Genetic testing can give 3 possible results: positive, negative, and uncertain. A positive result indicates a gene mutation was found that can cause an increased chance to develop some cancers, which might result in earlier or increased screening or other preventative measures for you. A negative result indicates no problematic spelling variant was found. This does not completely rule out the possibility of a hereditary cause, and your genetic counselor would recommend you continue to follow your doctors regarding treatment for your cancer, and/or screening based on your family history. A variant of uncertain significance (VUS) means a gene variant was found in the gene, but its potential impact on cancer is unknown at this time. These uncertain variants are non-actionable, so treatment and/or screening would be based on personal and family histories just like a negative result.
Benefits of Genetic Testing for Cancer
If genetic testing shows you have a mutation in a hereditary cancer susceptibility gene, this can be beneficial by giving you information about increased chances to develop certain types of cancer. This information can then help you and your doctor(s) guide your health care decisions and work together to determine the best possible steps to reduce your risk, including:
- Earlier and/or more frequent screenings. Begin routine screenings before the recommended age and at closer intervals than recommended for people of average cancer risk.
- Lifestyle changes. Opt for a healthy diet and daily exercise.
- Medications. Take medications as prescribed by your physician.
- Prophylactic surgery. Consider surgery to remove tissue that is at significantly increased cancer risk. One example is actor and filmmaker Angelina Jolie. She chose to have a preventive double mastectomy (breast removal) and a salpingo-oophorectomy (removal of fallopian tubes and ovaries) after learning she had the BRCA1 genetic mutation and a significantly increased risk of developing breast and ovarian cancer. This increased risk was due to the gene defect and a family history of cancer deaths, including her mother, aunt and grandmother.
In addition to helping you manage your own health, a positive genetic testing result can also provide valuable information for your family. Since these are hereditary gene changes, this means parents, siblings, and children of a person with a hereditary gene mutation also may carry the same genetic mutation. The exact chances for your family members to also test positive depend on the gene.
If you are a parent of a young child, knowing you have an inherited cancer can also help guide your child’s health care. You can talk with a doctor about when your child should consider genetic testing and whether your child also needs to take preventive action. Adult children should be provided with your test results so that they can discuss the information with their own doctors.
If you have been diagnosed with cancer and undergo genetic testing, the results can help your medical team determine the best treatment strategy. This may mean changing your surgery plans to a different type of surgery or taking different medications to target the cancer.
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