Genetic Testing and Genomic Testing: What’s the Difference?

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If you’re dealing with a cancer diagnosis, genetic testing and genomic testing are two important concepts to understand. They sound somewhat similar, but refer to the gathering of two different types of important information about the biology of a person’s cancer.

Both of these forms of cancer testing figure into “personalized medicine”, or matching treatment to the specific biological characteristics of a person’s cancer.

In this post, we’ll take a look at genetic testing vs. genomic testing, why both are important and how they figure into a cancer care plan.

What is Genetic Testing?

Genetic testing looks for specific inherited changes in a person’s genes that can increase their risk of developing cancer. Genetic testing is typically done on a sample of saliva or blood.

It’s estimated that inherited genetic changes are a contributing factor in 5-10% of all cancers.

There are different kinds of genetic tests. Some look for inherited variants in individual genes. Examples are variants in the BRCA1 and BRCA2 genes that increase risk for breast cancer and variants in the PALB2 gene that are associated with increased risks for breast and pancreatic cancers.

There are also tests that look for changes that could be indicative of an inherited cancer syndrome where patterns of certain types of cancer may be seen within families. Examples are Lynch syndrome and Li-Fraumeni syndrome. And there are panel genetic tests, which check for changes across a wide range of genes.

Why Consider Genetic Testing?

If you’ve already been diagnosed with cancer, genetic testing may be worth considering because it can give you information about your risk of being diagnosed with a new cancer down the road. That information can help with screening choices and other possible interventions.

In addition, genetic testing can sometimes help with treatment choices. And it can also provide information that may be pertinent for family members.

Individuals diagnosed with breast cancer at a relatively young age are one group that is generally advised to consider genetic testing. For these individuals, genetic testing would look for changes in the BRCA genes, as well as a number of other genes that are known to increase risk for breast cancer, although to a lesser extent than BRCA mutations.

I was diagnosed with breast cancer at age 35. At the time I was diagnosed (in 1993) testing for BRCA mutations was not yet available. I also did not have any family history of breast cancer. Over the years, having followed developments in genetic testing, I eventually decided to be tested. I’ve written about my experience with genetic testing in this post.

What is Genomic Testing?

Genomic testing–also referred to as genomic profiling or biomarker testing–looks for certain genetic changes that have occurred within the tumor tissue itself. These kinds of changes are specific to the tumor and are not inherited.

The information obtained through genomic testing can help determine whether an available targeted treatment is likely to be beneficial. Or it could help in matching an individual to a clinical trial that is relevant for their particular cancer.

Genomic testing is typically done on a sample of tumor cells after a biopsy or surgery. In some situations, it may be done through a blood draw.

How is Genomic Testing Used in Cancer Care?

Genomic testing is being used now in a variety of ways to match treatment more closely to the specific biological traits of a person’s cancer.

With targeted therapies, the idea is that the treatment should be both more effective and have a fewer side effects in comparison with chemotherapy because it targets the cancer directly.

There are now numerous cancer therapies, including targeted treatments and immunotherapies, that are matched to the presence of a biomarker. There are also lots of ongoing clinical trials of these kinds of therapies.

An example of a targeted therapy that is matched to the presence of a biomarker is the immunotherapy drug Keytruda (pembrolizumab). Keytruda has been approved for treatment of many types of cancer including skin cancer, lung cancer, bladder cancer and breast cancer. I’ve written about immunotherapy for breast cancer in this post.

Part of matching treatment to the biology of a person’s cancer is knowing when to avoid treatments that have toxicities and will not be beneficial. The Oncotype DX genomic test has now become standard for individuals with early stage hormone receptor-positive breast cancer. This test is enabling many in this group to avoid unnecessary chemotherapy treatment. I wrote about Oncotype DX in this post.

Although they are supposed to have fewer side effects, targeted treatments are not without toxicities. Some targeted treatments, including some immunotherapies, have significant side effects, and those receiving them need to be monitored closely.

Financial toxicity is part of the picture too. Genomic testing can be costly, and is not always covered by insurance. And targeted therapies are often extremely expensive, although the cost of an investigational therapy received in a clinical trial is normally covered by the trial sponsor.

For More Information

The NCI’s Biomarker Testing for Cancer Treatment is a helpful overview and includes information on stages and types of cancer in which genomic or biomarker testing is done, as well as a discussion of cost and insurance coverage.

The Cancer.Net podcast, “What is somatic genomic testing and how is it used in cancer care?” is a discussion of what individuals dealing with metastatic or advanced cancer need to know about genomic testing.

And in a blog post, also on Cancer.Net, a woman dealing with metastatic breast cancer shares her story of how identifying the mutations present in her cancer led to a treatment plan.

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