One way or another, cancer affects us all. Virtually everyone has had a family member, a friend or colleague who has been diagnosed with cancer. Maybe you have had cancer yourself. And sadly, we probably know someone who has lost their life because of cancer.
If you could take a genetic test to better understand your risk for certain types of cancer, would you? That’s a key question many patients consider at some point.
For some people, the answer is yes. A genetic test may provide new insights into your health – and shape the decisions you and your doctor will make together. But there are limitations to what these tests can tell you, and they may not be for everyone. Let’s take a look the pros and cons of genetic testing.
Screening for Cancer vs. Screening for Genetic Traits
“The first thing to know about cancer-related genetic testing is that it is not a test that will tell you if you have cancer,” explains Dr. Andrew Hoover, a family medicine doctor in Rhome. “It simply tells us whether or not you have certain genetic traits that increase your risk of getting cancer.”
That’s why everyone – whether you have had a genetic test or not – must still get regular, recommended cancer screenings, such as a mammogram and colonoscopy. Even if you have had a genetic test that shows you do not have specific cancer-related genes, you still need to get your regular cancer screenings.
Genetics 101
Before diving into genetic testing, let’s jump back in time to high school biology class on the day we learned about DNA, genes and chromosomes.
Deoxyribonucleic acid (DNA), present in all living entities on earth, is the material that provides genetic instructions for each being. DNA looks like a twisting ladder – a double helix – and contains four different bases. The order or sequence of these four bases determines genetic makeup.
A gene is part of the DNA responsible for making proteins. We get one copy of each gene from our mother and one from our father. This is how we get inherited traits, such as looks, eye color and build. Genes that have abnormal changes, or mutations, can increase the likelihood of certain diseases.
DNA is packaged into chromosomes, each of which contain a long strand of DNA with many different genes. Every cell in the human body contains 23 such chromosome pairs. Twenty-two of them are numbered chromosomes, while the 23rd is known as either an XX or XY chromosome—this is, of course, the chromosome pair that determines our gender. Each pair of chromosomes is made up of one chromosome from the mother and one from the father.
Genetic Testing in Health Care
In health care, there are several ways genetic testing is used:
- Newborn screening: This is the most common type of genetic testing. Newborns are screened to detect the presence of genetic and metabolic abnormalities that could lead to conditions such as congenital hypothyroidism or sickle cell disease. In the event the screening detects worrisome abnormalities, treatment can begin immediately.
- Diagnostic testing: For patients who are experiencing certain symptoms, a genetic test may be part of the diagnostic process. For example, genetic testing may be able to confirm a suspected case of cystic fibrosis.
- Carrier Testing: This may be done to detect recessive or hidden genes for certain hereditary diseases. The abnormal genes can be passed silently from generation to generation without detection. This testing can be done for persons considering pregnancy. If both partners of a pregnancy carry the same abnormal gene, there is a 25% chance the fetus can have the disease.
- Pharmacogenetics: This type of testing can help determine what medication may be most effective to treat specific conditions.
- Prenatal testing: Prenatal testing can determine if there are specific mutations in a baby’s genes, such as the ones that cause Down syndrome.
- Preimplantation testing: For people trying to become pregnant through in vitro fertilization, the embryos may be screened for genetic abnormalities before they are implanted in the uterus.
How is Genetic Testing Done?
A genetic test is done by taking a sample of blood, hair or skin. Some of the most common testing procedures include:
- Blood sample: Similar to getting blood drawn for a cholesterol screening, a needle is inserted into the vein and a tube of blood is taken. For newborn screenings, the baby’s heel is pricked and a small sample of blood is taken.
- Cheek swab: This simply involves taking a cotton swab and rubbing it on the inside of the cheek to get a biological sample.
- Amniocentesis: For prenatal testing, the doctor inserts a thin needle through the abdominal wall to retrieve a small amount of amniotic fluid (the fluid that surrounds the fetus) for testing. This test may also be conducted by taking a tissue sample from the placenta.
For any of these tests, the tissue or fluid sample is analyzed in a lab, where technicians look for abnormalities in chromosomes, proteins or DNA.
Predictive Genetic Testing
Genetic screening for cancer is a type of predictive testing, also called pre-symptomatic testing. A genetic cancer screening detects certain mutations that increase cancer risk. These mutations cause between 5% and 12% of all cancers.
Cancers Sometimes Caused by Genetic Mutations
Several cancers may be caused by specific genetic mutations in the BRCA1 or BRCA2 genes. These are known as the breast (BR) cancer (CA) genes, but they are also linked to increased risk of ovarian, pancreatic and prostate cancers, as well as melanoma (a type of skin cancer).
Breast and Ovarian Cancers
Mutations of the BRCA1 and BRCA2 genes are known to substantially increase risk for both breast and ovarian cancers. When working as intended, both genes produce proteins that repair damaged DNA – this is why they are known as “tumor suppressor” genes. Certain types of mutations to either the BRCA1 or BRCA2 genes may limit your body’s self-defense against damaged cells. This increases the risk of cancer.
We have two of each of these genes: one from each parent. A genetic mutation can be passed down from the father or mother. If a parent has a mutation, each of their children has a 50% chance of inheriting it.
While there is no guarantee that someone with a BRCA1 or BRCA2 mutation will develop cancer, there is no question that the odds are significantly increased, according to data from the National Cancer Institute.
Among all women, about 13% will get breast cancer at some point. For women who have a mutation in a BRCA1 gene, 55% – 72% will develop breast cancer by ages 70 – 80. Among women with a variant in a BRCA2 gene, 45% – 69% will develop cancer.
Similarly, ovarian cancer impacts 1.2% of all women. But for women with a variant in the BRCA1 gene, risk goes up substantially: 39% – 44% will develop ovarian cancer. BRCA2 variations also elevate risk, with 11% – 17% eventually getting ovarian cancer.
“Any woman can be tested for a BRCA gene mutation if they choose,” says Dr. Hoover. “Women whose families have a history of breast or ovarian cancer are definitely candidates for genetic testing and they should discuss it with their doctor.”
Men can also be tested for this genetic mutation. While male breast cancer is quite rare, a BRCA gene mutation increases risk. It can also increase risk of prostate cancer.
Lastly, BRCA gene mutations increase risk of pancreatic cancer and melanoma, a type of skin cancer.
Other Cancers
Lynch Syndrome is an inherited condition that occurs when one of the genes responsible for repairing DNA mutates. This genetic trait has been shown to increase risk of colorectal cancer.
Genetic mutations can increase likelihood of several additional cancers, including uterine, stomach, thyroid and kidney.
Of course, usually these cancers are caused by something other than genetics. In addition, it is possible to have a genetic mutation yet never actually get cancer.
Pros & Cons of Genetic Testing
There are several advantages to genetic screening for cancer. If the screening does not reveal any hereditary mutations, this may lead to additional peace of mind and reduce stress.
If the test does reveal a genetic mutation linked to cancer, the patient, in coordination with medical care teams, can modify health care screenings. For example, if there are mutations in the BRCA1 or BRCA2 genes, this may be a reason to begin mammography screening sooner and do it more frequently.
Similarly, an indication of Lynch syndrome would suggest colonoscopies should begin before age 45.
In addition, health care providers may recommend considering more aggressive steps to protect the patient’s health. This could include medications or even risk-mitigation surgery, such as a breast reduction or mastectomy, to further reduce risk of a future cancer diagnosis.
Drawbacks of Genetic Testing
There are downsides to genetic testing, as well. A screening that does not reveal a hereditary predisposition to cancer may create a false sense of security, especially when so many other factors can cause cancer.
Conversely, screening that reveals a genetic mutation may lead to over-treatment. The presence of a mutation does not automatically mean that a cancer diagnosis is inevitable. A positive result on a screening may lead to unnecessary treatments and added stress and worry.
Where to Test
While there are at-home genetic testing options, it’s probably best to test through your doctor’s office, for a few different reasons.
First, a decision to undergo genetic testing for cancer indicators should be a decision you make after discussion with your doctor.
When you get your results, you want to have your doctor analyze them and review them with you.
In some cases, insurance will cover the cost of testing when done through your physician – that likely won’t be the case when ordering a home-based test.
And while some home-based genetic tests are U.S. Food & Drug Administration-approved, there are plenty out there that are not. You don’t have to worry about quality and accuracy in the lab your doctor uses – and you can also be assured that patient privacy is respected at every step of the process.
Talk to Your Doctor About Testing
The ability to test for genetic traits that inform us about our health is one of many remarkable medical and scientific advancements we are fortunate to have available.
“Genetic testing is a valuable tool that we can use to help some patients, says Dr. Hoover. “But like any tool, it’s not appropriate in every situation – some patients simply don’t need to undergo genetic testing. Your doctor is here to talk through the pros and cons so you can make the best decision for your health.”
This article has been reviewed and approved by a panel of Privia Medical Group North Texas physicians.
This article contains information sourced from:
The U.S. Centers for Disease Control & Prevention
The National Human Genome Research Institute, National Institutes of Health
