What is Genetic Testing for Cancer?

With the rise of mainstream at-home genetic tests, many are curious about how their genetic makeup influences their risk for diseases like cancer. However, understanding genetic risk requires more expertise and precision than these kits currently offer. 

Genetic testing, coupled with genetic counseling, can identify patients’ hereditary risk for developing certain cancers, empowering them to make more informed decisions about their health and future. We spoke with Herbert Irving Comprehensive Cancer Center (HICCC) genetic counselors Elana Levinson, MS, MPH, CGC and Kimberly Hilfrank, MS, MPH, CGC, about why genetic testing and counseling is so important for cancer prevention, the types of tests offered, what to do with your results from a genetic test, and more.  

What exactly is genetic testing in relation to cancer? What can it tell someone? 

Only about 10% of cancers happen because someone is born with a hereditary predisposition due to a family history of cancer. Sometimes, there are “clues” in someone’s medical or family history, like a cancer diagnosis before age 50, that make us more suspicious of a hereditary predisposition being present. When we do genetic testing focused on cancer, we’re analyzing genes associated with hereditary risks of cancer. These are typically well-known genes that have specific guidelines in terms of cancer risks and screening.    

Most people know about the BRCA gene. What about other lesser-known genetic variants? 

There are a small number of genes we all have that, when working properly, protect us from developing cancer or fix issues that may occur in our DNA (tumor suppressor genes, mismatch repair genes, etc.) A mutation in one of these genes prevents it from doing its job so we test these to evaluate cancer risk. Lynch syndrome is actually more common than the well-known BRCA gene, about 1 in 300 people are carriers. This gene increases risk for various cancers including colon, endometrial, ovarian, and others as well. 

The testing you do is more comprehensive and precise compared to at home genetic tests. How does your sample collection process differ?  

Testing can be done via blood or saliva sample, though blood tends to have less of a failure rate because it’s easier to extract the DNA. It's a simple, minimally invasive blood draw, and we typically only need a small amount, usually just one tube. 

What can someone expect from a genetic testing and counseling visit?  

Usually, appointments last about an hour. A genetic counselor will spend the first 45 minutes with the patient asking questions about their medical history, previous cancer diagnoses and treatment, and any other cancer surveillance (mammography, colonoscopy, etc.) or chronic illnesses they’ve had in the past. We also get a three-generation pedigree, meaning we ask about their children, siblings, aunts, uncles, parents and grandparents. This gives us a good sense of patterns that could suggest hereditary causes of cancer, allowing us to then do a risk assessment. The risk assessment involves talking about which genes we could test or cancer syndromes we may be suspicious of, along with the benefits and risks of genetics.  

We also do psychosocial counseling to understand their support and what the potential results may mean for themselves and their family members. Sometimes patients opt out of genetic testing because it may not be needed after receiving genetic counseling on their risks 

If someone does decide to move forward with genetic testing, what are their next steps?  

We call the patient once we receive the results, which can be positive, negative, or uncertain. If the results are positive, the patient is offered a follow-up appointment to speak about the mutation in more detail. They also receive a letter that explains the results and includes recommendations for surveillance based on family history or genetic mutation. We help place referrals to other providers for positive test results as well, where they can then have more in-depth conversations with a specialist about their specific needs.  

What does an “uncertain” test result mean?  

It means that the lab found a genetic change, but they do not have enough data because it has not been seen in enough people yet. We can’t say if the genetic mutation is 100% harmful or benign. Medical management is not usually altered for an uncertain test result, patients would just continue their current screening surveillance based on their own clinical findings or family history. If the variant ever gets reclassified to harmful or benign because enough data has been obtained, we notify the counselor and patient. About 80% of variants get classified to be benign.  

How do I know if I should be considering genetic testing and/or counseling?  

Genetic testing and counseling should be considered if you have a history of cancer yourself and have never received genetic testing, or if you had genetic testing done years prior. It is also something to consider if you have a parent who had a cancer diagnosis, particularly at a young age, or if you have multiple family members that had the same type of cancer. In the past, guidelines and criteria about who can get testing were stricter. This has changed, and genetic testing is happening more. We’re happy to meet with anyone concerned about their own hereditary risk. It’s also important to emphasize that coming to a genetic counseling session doesn’t mean that testing is required. It’s a shared conversation with the patient and we really try to support how the patient wants to move forward after counseling.