In our webinar titled “Unlocking Precision Care: Genomic Testing for Breast Cancer Management,” medical oncologist Dr. Tiffany Avery explores how different tests can guide personalized treatment plans for breast cancer patients.
You can watch the full webinar below.
We’ve transcribed some of the key takeaways from this discussion to help guide your treatment decisions.
The following questions and responses have been lightly edited for grammatical purposes.
Q: What’s the difference between germline testing and somatic testing? Why should they both be considered when someone’s diagnosed with breast cancer?
A: This is a great question and absolutely fundamental because there’s a lot of confusion. We know that cancer is a genetic disease. If you start with basic cell biology, cells grow and divide and we have genes that control that process. When genes are working properly, the cells grow, divide, and stop when they’re supposed to.
When the genes don’t work the way they’re supposed to, cells get the ability to grow and divide out of control. They don’t stop when they’re supposed to. In a basic, simple term, that’s how you get a tumor.
When you read cancer as a genetic disease, it means that something has changed those genes. Something led to this tumor forming from a cell growing out of control.
The question before us today is where did that change in the gene come from?
It can be that you were born with it, so you inherited some change in one of these genes that control that process. It was already there when you were born and it makes you more susceptible to developing a tumor sometime in your life. Those are germline mutations. The way I like to think about it or tell people to think about it is with the word ‘line’ and think about the family line.
Germ means sex cells’ reproductive cells. It means mutations are passed down through families, so that’s germline. When you hear of germline testing, it means we’re looking for the changes that happened in those genes by way of inheritance through your family.
When we talk about the other set, a lot of terms can be used to describe it. Somatic is the one you mentioned, which is absolutely correct. You might also hear genetic testing, genomic testing, next-generation testing (NGS), and all of those terms mean the same thing. We want to see what happened in that cancer cell specifically.
We’re taking that cancer cell and we’re looking at the genes in that cell for the mutations. It wasn’t that you were born with certain genetic mutations. Stuff happened along the way, the stuff is what we call carcinogens. When you hear that something is carcinogenic or is a carcinogen, that means it’s something that can cause damage to DNA and lead to changes in the cell.
When we’re looking at genomic testing, we’re looking at that cancer cell to say, “Oh, these are the mutations that happened in these specific genes that cause the cell to grow out of control and become a tumor.”
I hope that sheds some light on it. When you hear germline, we’re talking about your family line, which you were born with. Anything else is what happened to that cell after you were born that caused it to grow out of control and form a tumor.
The other point that I want to make is that when we talk about germline, depending on the study, only 5 to 15% of cancers are inherited. The majority of cancers happen because of genetic mutations that have happened along the way in the course of living your life and are not hereditary. You weren’t born with them.
It’s still important to do germline testing, even though it’s not the majority of cancers, but I just wanted to make that clear from the start.
The reason that becomes important is when you hear about targeted therapies. Targeted therapies are where oncology has been and will continue to go. All that is an understanding of those very particular mutations: what they’ve done in the cell and how they can be targeted specifically to shut the cell down.
Q: What’s the difference between targeted therapies versus chemotherapies?
A: Chemotherapies kill actively dividing cells. So tumor cells are actively dividing, but so are your healthy cells. When you talk about chemotherapy, you get the side effects that come with it: the vomiting, the diarrhea, the hair loss. All of that is because your healthy, normal cells are being killed along with the tumor cells.
When we’re talking about targeted therapies, we’re talking about only zeroing in on what is going on in the cancer cells and leaving the healthy cells out of it. That’s why the targeted therapies are often better tolerated, or there’s a different profile of tolerance between the chemotherapy and the targeted therapy.
Q: How can genomic testing of a tumor help guide a treatment plan? Are there differences when it comes to different stages of breast cancer?
A: Genomic testing does help guide treatment planning when it comes to medical oncology, which is kind of my wheelhouse where you get treatment with medications rather than surgery or radiation, so we’re talking about drugs. How that helps is we’re able to identify certain targets within that cell and see if there are medications approved for that specific target or that pathway.
When it comes to early cancer versus metastatic cancer, I’m going to start with metastatic because it’s more in line with what I just described. With metastatic patients, we want to know what all of our targeted therapy options are. Genomic testing, NGS testing, somatic testing, or any of those things are done on that tumor to identify what targeted therapies could work for this tumor specifically.
Contrast that with early breast cancer, the genomic tests that are used in early breast cancer look for the expression of certain genes to tell who needs chemotherapy and who could safely omit chemotherapy. Those tests include Oncotype DX or MammaPrint, for example.
Those tests look for the expression of certain genes to tell us who needs chemotherapy and who could safely omit chemotherapy. There’s very little benefit based on the genes that the tumor is expressing, so it’s a little bit more nuanced and different when it comes to the applications of genomic testing in early-stage cancers versus late-stage cancers.
View the entirety of Dr. Avery’s Ask the Expert webinar here.