Genetic Testing for Patients With Breast Cancer: Jacqueline Mersch, Genetic Counselor

Jacqueline Mersch, MS, CGC.

This interview has been conducted in partnership with the National Breast Cancer Foundation (NBCF). Recognized as one of the leading breast cancer organizations in the world, NBCF is Helping Women Now® by providing early detection, education, and support services to those affected by breast cancer. A recipient of Charity Navigator’s highest 4-star rating for 14 years, NBCF provides support through their National Mammography Program, Patient Navigation, breast health education, and patient support programs. For more information, please visit

Jacqueline Mersch, MS, CGC, is a genetic counselor and manager at UT Southwestern Simmons Comprehensive Cancer Center. Today she will be discussing genetic testing for patients with breast cancer.

Oncology Data Advisor: Welcome to Oncology Data Advisor. Thank you for being with us today, Jacqueline.

Jacqueline Mersch, MS, CGC: Of course. Thank you for having me.

Oncology Data Advisor: Can you tell us a little bit about what you do as a genetic counselor?

Ms. Mersch: First, it may be helpful to understand what kind of training I have as a genetic counselor. After I completed my master’s degree in genetic counseling, I sat for our board exams. I’m certified to perform genetic counseling across a variety of different specialties, but I’ve chosen to specialize specifically in oncology and cancer genetics.

Typically, in an oncology setting, when I’m meeting with patients for their genetic counseling appointment, we’re collecting their personal and family histories of cancer in order to perform a risk assessment for that patient’s chances of hereditary cancer. Then we use this information to educate patients on cancer genetics, which leads to a discussion on decision making with regards to genetic testing.

We discuss the risks, the benefits, and the limitations of genetic testing, to help the patient make the decision that’s right for them. For the patients that go forward with genetic testing, we help them interpret those results when they’re available, particularly with regards to future cancer risks for themselves, management recommendations, as well as the implications for their at-risk family members.

Oncology Data Advisor: What are some of the recent advances in genetic testing for breast cancer?

Ms. Mersch: The world of genetics is rapidly evolving for breast cancer, as well as all cancer types. It’s been many years since the BRCA1 and BRCA2 genes were first discovered in the 1990s. Within the last five to 10 years, the availability of different cancer genes for clinical testing has really expanded. We can frequently order panels when we do genetic testing that include over 80 different genes related not only to breast cancer, but also to a variety of different hereditary cancers and tumors. We’re able to get a comprehensive overview of patients’ risks for developing hereditary breast and other types of cancers.

Along those same lines, with the advancement of larger panels, the overall cost of genetic testing has decreased. We’ll hear patients, either through their providers or during the appointment, expect that genetic testing is going to cost them thousands of dollars. An important part of discussing genetic testing with the patient is the cost of testing. In our experience, insurance typically covers appropriate, clinically indicated testing. Additionally, if patients want to pursue testing, either outside of insurance, or perhaps if they’re underinsured or uninsured, there are discounted rates available through many labs, as well as financial assistance programs that genetic counselors are well-versed with getting patients plugged into.

Now from a more technical standpoint, one of the more exciting clinical developments when it comes to hereditary cancers, including breast cancers, has to do with RNA testing. Typically, when we’ve done genetic testing, we’re looking at the DNA sequence, that genetic code for specific genes that we know are related to a predisposition of breast and other types of cancer. But more recently, labs have been able to provide clinical analysis through RNA testing.

RNA is the downstream product of DNA. By looking at that RNA, the labs are able to actually analyze larger regions of the genetic code, different areas that were not previously accessible through DNA testing, which has helped to uncover rare mutations or pathogenic variants that just previously were not able to be identified, thereby helping the diagnostic yield of the genetic testing.

Additionally, this RNA testing can help clarify some previously found uncertain results. Oftentimes, through genetic testing, we’ll find something called a variant of uncertain significance. Depending on where that variant is located, for example, right at a border of an intron and an exon, RNA testing can be used to determine if that variant actually leads to a disease-causing error in the genetic code, thereby becoming a positive result, versus just being a benign variation or a negative result. This RNA technology can help to clarify some of the uncertainty that comes up when we do certain genetic testing. It’s exciting to have more options available with our standard genetic testing.

Oncology Data Advisor: What are some of the factors that go into determining which individuals at risk for breast cancer should undergo genetic testing?

Ms. Mersch: A great question. It’s something that’s particularly at top of mind when we’re going into Breast Cancer Awareness Month, but also something that is part of a lot of people’s considerations, both in clinics and just on a personal level. The first risk factor would be a personal diagnosis of cancer, now even within breast cancer—we’re looking at the type of breast cancer. Is it ductal versus lobular? Is it a triple-negative? Is it estrogen-positive? Or even is it metastatic? All different types of breast cancer can factor into the risks for a hereditary cause.

We’re also keeping things in mind, like age. Typically, when we see cancer happening at younger ages, under the age of 50, for example, we know that there could be the potential for a hereditary or a genetic etiology compared with cancers that are diagnosed closer to the average age, in the 60s.

Additionally, when we’re thinking about risk factors for a hereditary cause, we’re thinking genetics, so family history of cancers is important.

There are a couple common misconceptions that I’d like to address in thinking about family history. We have to make sure to include both sides of the family, the maternal side and the paternal side, because we inherit our cancer genes from both sides of the family. A woman could inherit a hereditary risk for breast cancer from her dad’s side of the family. We also have to keep in mind that it’s not just a family history of breast cancer that could lead to a hereditary risk. This goes back to the different cancer genes that can predispose to breast cancer also often predisposing to other types of cancer. If we were to see a family history that includes pancreatic cancer, ovarian cancer, prostate cancer, or even colon cancer, those could also be signs that there may be an underlying hereditary risk that could include the chances for breast cancer.

Oncology Data Advisor: What are some of the most common questions you encounter from individuals undergoing genetic testing, and how do you counsel them?

Ms. Mersch: That’s a great question and something that we get frequently. Patients who have already been diagnosed with cancer may wonder, “What would be the point of this, I’ve already had cancer? What is genetic testing going to help me with?” To them I’d say, “The genetic testing could help us understand potentially the reason why.” I think that’s a very common question patients have after a diagnosis, which is “Why did this happen?” Genetics could help answer that question or reduce the chances of a hereditary cause.

Also, genetic testing may help with treatment decisions for that diagnosis. If genetic testing reveals that there would be a higher risk for a second primary breast cancer, for example, different options may be considered when deciding on a breast cancer surgery to mitigate that future risk. The patient may also qualify for different therapy options if there’s an underlying genetic cause for that cancer.

Additionally, we like to make sure that patients understand that even if they’ve been diagnosed with a cancer, there could be a higher risk for another cancer in a different part of the body. If we have that information now, we can oftentimes take steps to be proactive in managing that elevated risk.

Then finally, another important outcome with genetic testing is the information that we can give to a patient to share with their family members. Typically, if we find a cancer gene mutation in a patient, it did not start as a brand new mutation, also known as a de novo mutation, in that patient; it would have been inherited from a parent who inherited it from a parent, and so on and so on. There can be other individuals in that family who are also at risk for hereditary cancer that could benefit from this patient’s genetic testing process.

About Jacqueline Mersch

Jacqueline Mersch, MS, CGC, is a certified genetic counselor at UT Southwestern Simmons Comprehensive Cancer Center. She also counsels patients at Moncrief Cancer Institute. Ms. Mersch manages the UT Southwestern Cancer Genetics Program in Fort Worth, Texas, and sees patients at UT Southwestern clinics. Her research has been published in several journals, including JAMA and Cancer.

Transcript edited for clarity. Any views expressed above are the speaker’s own and do not necessarily reflect those of Oncology Data Advisor. 

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