Genomic Testing for Personalized Cancer Treatment

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

No two cancers are the same, even if they are in the same part of the body, such as breast or lung cancer. Tumors have unique genetic properties that make them act and grow in a certain way.

Genomic tests analyze your cancer's genes to treat it more precisely. These tests can help your doctor match you to treatments that are more likely to work against your cancer, and cause fewer side effects than standard cancer treatments like chemotherapy or radiation.

Treating cancer based on your genes is called "personalized medicine" or "precision medicine."

Genes are the directions that tell your cells how to make different proteins. These proteins direct all the functions that make your body run. When a cell's genes change, or mutate, it makes different proteins. The new proteins sometimes make cells divide faster, which is how cancers start.

Targeted cancer treatments are aimed at the gene changes or new proteins that help cancer cells grow. Some of these treatments block the signals that cancer cells use to multiply and spread. Others cause the cancer cells to die.

Genomic tests look for certain genes in your cancer, to help your doctor find the targeted treatment that will work best against it. For example, about half of melanoma skin cancers have a change to the BRAF gene. These cancers make a protein that helps them grow faster. BRAF inhibitors are medicines that attack the BRAF protein to slow or shrink melanoma.

Other examples of targeted therapies are:

  • Human epidermal growth receptor 2 (HER2) inhibitors that treat HER2-positive breast and gastric cancers
  • Tyrosine kinase inhibitors (TKIs) that treat chronic myeloid leukemia (CML) with BCR-ABL gene mutations
  • Epidermal growth factor receptor (EGFR) inhibitors that treat colorectal and lung cancers with EGFR gene mutations


Learning that you're finally cancer-free after treatment can come as a big relief. But it's possible you might have a "recurrence" of your cancer, which means it comes back months or years later. In the past, it was hard for doctors to know whether someone's cancer might return, which led to a lot of uncertainty.

Doctors used to give chemotherapy to most women with breast cancer to lower the chances of a cancer returning. But that meant that some women who didn't need chemotherapy to treat their initial cancer got it anyway and had to deal with its side effects.

Genomic tests have made preventing cancer recurrence much more precise. These tests help your doctor predict whether your cancer is likely to come back. If you're at low risk for a recurrence, you may be able to avoid more treatment. If you're at high risk, your doctor might recommend chemotherapy or other treatments.

One of the most common genomic tests for breast cancer checks a group of 21 genes in a sample of tissue from your cancer. This test can show your doctor how likely your cancer is to come back in the next 10 years, and if chemotherapy might prevent your cancer from returning.

Another genomic test, called the Breast Cancer Index test, checks 11 genes. Both of these tests are for people with hormone-receptor-positive breast cancer. The Breast Cancer Index can help predict whether your cancer might come back in 5 to 10 years. If your cancer is likely to return, staying on hormone therapy for 5 more years might prevent it from coming back.

Cancer treatments like chemotherapy and radiation kill cancer cells and stop them from dividing. But in the process, they also damage healthy cells. That damage can lead to side effects such as hair loss and infections.

Using genomic tests to match you to a cancer therapy makes your treatment more precise. By targeting cancer cells and avoiding healthy ones, targeted therapy might help you prevent or limit side effects.

Some targeted treatments are already approved. Others are being studied in clinical trials. These studies are a way for researchers to learn whether a new treatment is safe and if it works.

A clinical trial could be a way for you to try a new treatment that matches your cancer's genomic profile. Ask your doctor if any clinical trials are a good fit for you.

If your doctor prescribes a targeted cancer treatment based on the results of your genomic tests, ask questions. Find out how this treatment might help you and what side effects it might cause.

You can also meet with a genetic counselor. The counselor will explain the results of your genomic tests and guide you through your treatment options.