top of page

What is Genetic Testing in Cancer?

Understanding and knowing how it can help with screening and treatment planning.

“Using computational reconstruction methods, we were able to estimate the order and timing of genetic events that lead to cancer. We found that these genetic events often occur many years before the tumor is detected.”— Ignaty Leshchiner, Broad Institute. The ICGC/TCGA Pan-Cancer Analysis of Whole Genomes Consortium Nature 578, 82-93 (2020)

Nearly 10% of all cancers are hereditary and therefore access to genetic testing and

counseling both before and at the time of diagnosis is important.

The identification of patients before a diagnosis of cancer allows for optimal surveillance and early detection and prevention of cancer.

Genetic testing can provide relevant information that can help decide future steps for the patient as well as close relatives but the information must be interpreted by a trained professional.

Research shows that the incidence of germline mutations that cause hereditary cancer ranges from 5% to 10% among  breast, colorectal, endometrial, pancreatic, and prostate cancer, and as high as 18% among those with ovarian cancer.

In other words, when it comes to inherited pathogenic mutations that lead to cancer,

new data shows that there is significant variability in gene expression, and a higher incidence

than previously recognized among individuals diagnosed with cancer.

Therefore, there is an increased need for access to genetic counseling and testing. Lack of awareness of the relevance of genetic testing as well as reluctance on how to initiate these types of discussions has led to about 1.2–1.3 million women in the United States who qualified for breast cancer genetic testing but did not receive it! It is important to understand that cancer genetic testing is different from some other types of testing because a positive test result does not always mean that you will get cancer. If you test positive for a variation in a cancer gene, it means you are more likely to get cancer. Several factors influence whether a given person with the mutation will actually develop cancer.

Two common factors that influence cancer development are:

1. Penetrance 

2. Expressivity

When not all people who carry a mutation go on to develop the disease associated with

that mutation, it is said to have incomplete or reduced penetrance. Hereditary cancer syndromes can also vary in their expressivity, which means people who inherit the mutation may vary in the extent to which they show signs and symptoms of the syndrome, including the development of associated cancers. Other factors that can influence development of cancer include lifestyle factors and environmental risks, for example smoking, asbestos exposure etc.

The results of genetic testing is often more informative if it can begin in a family member with a previous or current cancer diagnosis. 

 If a person in the family has already been found to have an inherited cancer

susceptibility syndrome, then any family members who could have inherited the variant should consider genetic testing, even if they have not had cancer since knowing about their risk may help them to prevent future cancer. Using a blood or saliva sample, the genetic test analyzes genes to see if there are any  mutations that may increase your risk of cancer.

Genetic Testing & Counseling

It is not just important to have the testing done; it is equally important that you

understand what the reports can mean. A trained genetic counselor can appropriately explain much of the uncertainty about whether you should have testing, which test to order, and what the test results mean for you and your family. This is the most reliable way to obtain up-to-date information and to formulate a plan.  Traditional counseling models include a pre-counseling session to review a multigenerational pedigree, review of the implications of the testing for patients and family members, and selection of the genes that should be included in the testing. Post-test counseling includes disclosure of the results within the appropriate framework of patient history and further recommendations for cancer monitoring, local therapy options, and identification of family members who may benefit from testing. The counseling session will include evaluation of your family health history and about risks for inherited cancer, as well as screening and management for those in your family who are at increased risk. If genetic testing is available, the counselor will tell you about the tests and help you decide if testing would be useful to you.

Here is a checklist of questions that can help you prepare for your counseling


  • How likely is it that I have a BRCA 1, BRCA 2 mutation, Lynch syndrome or another cancer-related mutation?

  • What is the testing process like and how long does it take to get answers?

  • Does the test provide information about my risk for other diseases besides cancer?

  • If I haven’t been diagnosed but I test positive for a cancer-related mutation, does that mean I am going to be diagnosed with cancer? 

  • If I haven’t been diagnosed with cancer and I test negative for a cancer-related mutation, does that mean my cancer risk isn’t higher than average? 

  • Is it possible for my results to be uncertain or indeterminate? What does that mean? 

  • If I’ve already been diagnosed with a certain type of cancer, can genetic testing help predict whether the cancer comes back? 

  • How does knowing my cancer risk help my family members? How should I advise them? 

  • Will you also talk to my family members about their risk based on my results?

  • Does health insurance pay for the test? Can my insurance company increase my rates if I test positive?

  • If I get genetic testing now, do I need to get tested again in future? 

  • Are there support groups for my type of genetic risk that I can join?

  • Will the counseling include risks that the mutation may have to my fertility?

Genetic testing for risk of hereditary cancer can help patients make important decisions

about screening, prevention or early detection. Speak to your doctor or healthcare team for what is the best route for you.

12 views0 comments

Reason to Hope

There is new research from Brigham and Women’s Hospital that indicates a Western-style diet that is rich in red and processed meat, sugar and refined grains/carbohydrates is tied to higher risk of colorectal cancer through the intestinal microbiota.  Gastroenterology, 2022;DOI:10.1053/j.gastro.2022.06.054 

bottom of page