Using Genetic Testing to Help Prevent Colon Cancer

March 27, 2017

In this interview we discuss the role of genetic testing in patients with colon cancer.

In this interview with Elena M. Stoffel, MD, MPH, of the University of Michigan Comprehensive Cancer Center, we discuss the role of genetic testing in patients with colon cancer.

 -Interviewed by Ian Ingram

Cancer Network:Walk us through the value of genetic testing in patients with colon cancer, how can the results of these tests inform the clinician?

Dr. Stoffel: One of our best approaches at preventing colon cancer is actually being able to identify people who are at increased risk, and when we think about how we generally identify people at risk, we usually go by their age and their family history. Genetic testing offers us an opportunity to go beyond that and identify that small group of patients who has a cancer risk that is orders of magnitude higher than the rest of the population. How do we best identify those patients? Where we are right now is we usually start with patients who have a colon cancer diagnosis, and if we identify patients with a colon cancer diagnosis that meet certain high-risk criteria, we can offer genetic testing to those individuals. Once we identify a genetic predisposition syndrome, then we can test other family members who may not have cancer yet in order to be able to prevent their cancer diagnosis in the future.

Cancer Network:For family members who are tested and are found to have similar genetic predisposition syndromes, what would be the recommendations to help prevent them from getting a cancer diagnosis?

Dr. Stoffel: What is interesting is that in certain hereditary cancer syndromes, we know very well what we need to do differently. For instance, in Lynch syndrome-one of the most common hereditary cancer syndromes-these patients have a very high risk for developing cancer over the course of their lifetime. We know that if we start doing colonoscopies between the ages of 20 and 25, and repeat them every 1 to 2 years, we can dramatically decrease cancer incidence almost back to the general population levels.

Cancer Network:For the patient that already has colon cancer, what other information might be gleaned from a genetic test that can inform treatment decisions?

Dr. Stoffel: One thing that’s important to recognize is that we can do genetic testing on either tumor DNA or an individual’s germline or constitutional DNA. Tumor testing is now becoming pretty mainstream. We commonly send off tumors to look at the mutational profiles. The tumor mutational profiles can also sometimes tell us what’s going on in the germline. For instance, if an individual has a germline mutation associated with defective mismatch repair, the tumors can demonstrate that by looking hypermutated, and so often looking at the tumors can give us a clue as to what’s going on in the germline. I think right now as we do testing very separately, for the tumor and for the germline, it’s important to recognize that they can inform each other and help us take better care of our patients.

Cancer Network:Is that something that is being worked on, the marrying of those two?

Dr. Stoffel: Right now a lot of companies that do tumor testing do only the tumor and not the germline, but other groups now are starting to recognize the value of sequencing the tumor paired with the germline because when you find something in the tumor and you see it in the germline, then you can actually make that genetic diagnosis.

Cancer Network:Is there anything else you would like to add?

Dr. Stoffel: Often when we are taking care of a patient with cancer, we are focused solely on that person’s cancer and on treating that cancer. But it’s so important to take a step back and look at the rest of the picture, look at the family history, look at the patient’s history, and see if we can find clues as to what may have led to that cancer development, which can help us prevent future cancers in that person or their family members.