What Is Genomic Testing in Cancer?

Medically Reviewed by Laura J. Martin, MD on July 23, 2023
3 min read

Genomic testing is one method your doctor can use to predict how your cancer will grow and which treatments might work best against it. It's sometimes called "DNA sequencing." The test looks at all your genes rather than a specific one.

Genes are pieces of DNA that hold the codes for making proteins -- the instructions that make your body run. Your genes are housed along threads called chromosomes inside each of your cells. The genes in your cells -- about 30,000 of them in total -- make up your genome.

Changes to your genes called mutations could make you more likely to get cancer, and help the cancer grow and spread more quickly. Some of these mutations are passed down from your parents to you. Others formed over your lifetime and are only in your cancer.

You may hear your doctor talk about "genetic testing," as well as genomic testing. Although they both involve testing of genes, they don't work exactly the same way.

A genetic test looks for inherited gene mutations from a sample of your saliva, cells, or blood that could affect your cancer risk. Your doctor might use a genetic test to:

  • Help predict your risk of getting cancer
  • Help predict your outlook if you do get cancer
  • Find out whether certain treatments will work against your cancer

For example, if the BRCA1 gene mutation runs in your family, your doctor might recommend that you get a genetic test. If you do test positive, you'll know that you're at higher risk for breast cancer and you may need extra screening.

A genomic test looks more widely at what's called your genome -- your full set of genetic "code" or instructions. It checks for gene mutations in your cancer to predict how it might act. A genomic test could help your doctor tell how fast-growing your cancer might be and how likely it is to spread. Your doctor uses a sample of your blood or tissue removed from your cancer to do this test.

Tumor profiling, also called tumor genomic profiling, is a way to personalize your cancer treatment. It looks at a sample of your cancer cells for unique gene changes that help the cancer grow and spread. Your doctor will do a biopsy to remove the sample of cells needed for this test.

Your doctor can use your test results to figure out which treatments are most likely to work best against your cancer. Matching the therapy to your genes makes your treatment more precise, which might also lower your chances of having side effects.

Some cancers grow and spread more quickly than others. By looking at your DNA, genomic testing can give your doctor an idea of whether your cancer is likely to grow slowly or if it will be more aggressive and spread quickly. 

This information can help your doctor plan out the best treatment strategy for you. A faster-growing cancer will need more aggressive and fast treatment, but a slow-growing cancer may not need treatment right away. Your doctor might monitor you instead. Waiting could also help you avoid the side effects that treatment could cause.

If your doctor recommends genomic testing, ask why they think it's a good idea for you. Find out how your test results will be used to diagnose and treat your cancer, and what that could mean for your outlook.