A certified genetic counselor discusses the role of genetic testing in gastrointestinal cancers.
In oncology, genetic testing continues to become more popular as it can have major treatment implications for patients with gastrointestinal (GI) cancers. However, the results are not always easy for nurses and other healthcare providers to decipher, especially as researchers are still building databases of what genetic variations are “normal” for certain groups of people, and which could potentially be disease-causing.
OncLive®, a sister publication of Oncology Nursing News®, sat down with Jennifer Geurts, MS, CGC, a certified genetic counselor at the Medical College of Wisconsin, to discuss these issues and unanswered questions.
Can you provide an overview on the role of genetic testing in GI cancers?
There are 2 different types of genetic testing. Germline genetic testing [is] where we’re evaluating to see if the patient has a hereditary predisposition to cancer—something they would have inherited from either their mother or their father's side of the family, typically. That is contrasted with somatic testing, or molecular profiling, where we’re doing genetic testing in a tumor.
A couple of different methodologies are used, either next-generation sequencing, RNA sequencing, or proteomics, to analyze the changes that have occurred in the tumor and what treatments may be most effective in fighting that cancer.
Is genetic testing done within the healthcare facility or sent to a lab?
Most of the testing, whether it’s germline genetic testing or molecular profiling on a somatic tissue, is typically sent out. There are a small handful of laboratories in the nation that specialize in doing this sort of testing. It’s rather involved and can be costly. [Testing] can range anywhere from a couple hundred dollars to a couple thousand dollars, depending on the test that’s pursued. So most of these tests are sent out to specialty laboratories.
What is the status of genetic testing? How common is it, and how do you see its role evolving?
When it comes to germline genetic testing, there are several reasons that we pursue [it]. One is if we can better care for the patient and if the genetic test is going to impact their management. Sometimes genetic testing may help to inform what kind of surgery a patient should have or what kind of medications they need to be taking if they’re newly diagnosed with cancer.
For patients who don’t have cancer, genetic testing can also be valuable to help inform us what sort of screening we should be doing to detect cancer early or even discuss prevention options so we can possibly do something to prevent that cancer from happening altogether. An example of that would be when we’re doing breast cancer gene testing for families that have a history of breast and ovarian cancer. Typically, what we’re trying to do is identify people who may be at a higher risk for cancer in the family. In the example of ovarian cancer, if a woman is done having children and getting closer to menopause, we can remove the ovaries and [fallopian] tubes to prevent ovarian cancer from happening in those gene mutation carriers.
How can providers interpret the results of genetic testing? Do you think this could be made clearer?
Interpretation of genetic test results is challenging. Our understanding of genetics and genomics evolves, so we learn more every year as more people are tested, and we have more of an appreciation of the complexities of genetics both in the germline and the somatic cells. In interpreting testing, the one thing we have to appreciate is that there is a lot of variation in DNA, and not all variation is bad. We really have to rely on the laboratories where the genetic testing is being performed to make sure that there is a quality in the interpretation of the variants so that we can understand which variants are going to be classified as pathogenic that cause disease, and then which variants are benign, also called polymorphisms, that don’t cause disease and are tolerated.
That complexity is there. We need more data analysis and more understanding of reference sequence in the general population, different ancestries, and ethnic populations to know what normal variation looks like so we can help interpret when we do have a variant, if that truly is leading to cancer or not.