Pharmacogenomics in Cancer Treatment
Before starting treatment for cancer, doctors can test for certain gene and protein changes to help determine which treatments are likely to work best. One way to do this is through pharmacogenomic testing. It is part of an approach to care known as precision or personalized medicine.
- What is pharmacogenomic testing?
- Why inherited gene changes matter in cancer treatment
- How is pharmacogenetic testing done?
- How accurate is pharmacogenomic testing?
- Is pharmacogenomic testing the same as biomarker testing?
- Is pharmacogenomic testing the same as pharmacogenetic testing?
- Questions to ask your doctor about pharmacogenomic testing
What is pharmacogenomic testing?
Pharmacogenomic or PGx testing looks at specific genes in a person’s DNA to help predict how well a treatment might work for them.
It works by looking at a person’s inherited genes, not gene changes in the cancer itself. It helps show how a person's body breaks down, absorbs, and uses medicines. This information can help doctors understand how well a medicine or cancer treatment might work in a person’s body and how they might react or respond to a cancer treatment.
By helping match people with cancer to the right treatment, and the right dose at the right time, pharmacogenomic testing can guide cancer treatments for better outcomes.
What are genes?
Genes are pieces of DNA inside each cell in your body. Genes tell the cell how to make the proteins it needs to function. Each gene contains the code (instructions) to make a certain protein, and each protein has a specific job in the cell. Learn more in Genes and Cancer.
Why inherited gene changes matter in cancer treatment
Some inherited gene changes can affect how your body metabolizes, or processes, medicines. For example, certain gene changes can affect:
- How fast or slow your body processes a medicine. If your body breaks it down too slowly, the medicine can build up and cause side effects. If it breaks it down too fast, the medicine might not work well.
- How your body responds to the medicine. This helps to know how well it may or may not work for you.
- How the medicine is absorbed by the body. This includes how it is carried through the blood and how the leftover waste is removed from your body. This might affect the amount or dose of a medicine that is safest to give.
- How likely you are to have side effects from specific medicines. Sometimes this can affect how much of a treatment should be given. Or it can help know what side effects to expect so they can be prevented and managed, if possible.
Pharmacogenomic testing looks for these gene changes to help choose the best treatment plan for each person.
How is pharmacogenetic testing done?
The procedure for pharmacogenomic testing is usually non-invasive and fairly simple.
First, a member of your health care team will collect your DNA in one of these ways:
- By rubbing a cotton swab on the inside of the cheek to collect cells
- By having you spit into a tube for a saliva sample
- By drawing blood
Next, your health care team will send the sample (specimen) to a genetic testing lab for analysis by specially trained experts. Your DNA is pulled out (extracted) and looked at under a microscope for certain gene changes. Examples of gene changes looked for in pharmacogenomic testing are CYP2D6, CYP2C19, DPYD, and TPMT.
Finally, a doctor or pharmacist trained in genetics, or a genetic counselor, will interpret the results of the testing. They will generate a report that shows if and how your genes might affect your response to certain medicines or treatments. For example, the results might say:
- Whether your body processes (metabolizes) medicines faster or slower than normal
- If you need a lower or higher dose than usual
- Whether you are at higher risk for side effects from certain treatments
How accurate is pharmacogenomic testing?
Research shows that pharmacogenomic testing is generally very accurate. Studies report these tests can correctly detect specific gene variants with over 99% accuracy in many certified labs. And because a person’s DNA doesn’t change, pharmacogenomic testing doesn’t need to be repeated.
However, pharmacogenomic testing isn’t useful for all diseases, including some cancer types. It also may miss rare or newly discovered gene variants, and variants that are more common in certain ethnic groups.
More research is still needed to understand more about how each gene variant affects different treatments.
Is pharmacogenomic testing the same as biomarker testing?
Pharmacogenomic testing and biomarker (molecular) testing are not the same, though both are used to help match people with the most effective and safest treatments for them.
The main difference is what is being tested:
- Pharmacogenomic testing looks at a person’s inherited genes, using healthy cells. It helps show how the body processes certain medicines.
- Biomarker testing looks for gene changes in cancer cells. These changes can help show which treatments may work best.
Biomarker testing is usually done at the time of diagnosis, using samples collected during a biopsy or surgery. It can help your doctor learn more about the cancer itself and whether it might respond to certain targeted therapies or immunotherapies.
For people with cancer, both biomarker and pharmacogenomic testing can guide decision-making by providing a more personalized treatment plan.
Is pharmacogenomic testing the same as pharmacogenetic testing?
Pharmacogenomic testing and pharmacogenetic testing are not the same, though they are closely related. Both can help predict how a person might respond to certain medicines.
The main difference is the scope of the testing:
- Pharmacogenomic testing looks at many genes at once and how they work together to affect drug response.
- Pharmacogenetic testing focuses on a single gene and how it might interact with a specific medicine.
Pharmacogenetic tests are often less expensive and results come back fairly quickly, so doctors may use them when they need to check for a specific gene that might interact with a certain medicine.
To guide decisions about cancer treatment, pharmacogenomic testing is more often done. Its broader focus looks at the target of the medicine (such as a tumor), how the medicine gets to the target, and how your whole body might respond to the treatment.
Questions to ask your doctor about pharmacogenomic testing
Not everyone with cancer needs pharmacogenomic testing. Your doctor might recommend it if your treatment options could be affected by how your body metabolizes certain medicines. Here are some questions to ask:
- Do I need pharmacogenomic testing done to find the best treatment for me?
- Have you done this testing already on me? If not, will you do it and when?
- What information will the tests help you find out?
- Will the results of this testing mean I will need more tests?
- How is my information kept private?
- How much will the tests cost? Will my insurance cover them?
- Will these tests help us choose which treatments are best for me?
- If testing shows a specific treatment might be best for me, how much would this treatment cost? Will my insurance cover it?
Learn more about what questions to ask in Understanding Your Options and Making Treatment Decisions.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: July 18, 2025
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