When to get biomarker testing for cancer

Screening

Routine cancer screening is proactive testing for certain cancers in people who don’t have symptoms. Screening may help find cancer earlier, or it may find changes that could become cancer and should be monitored.

Screening guidelines and recommendations often depend on things like age, the body parts you have (for example, whether you have a cervix), your personal and family health history, and genetic risk factors. If you have symptoms or a new concern, your doctor may recommend diagnostic tests instead of (or in addition to) routine screening.

Cancer screening can involve a variety of test types. Some screening tests look for biomarkers, such as blood tests like Prostate-Specific Antigen (PSA) testing for prostate cancer, or stool tests like Fecal Occult Blood Testing (FOBT) for colorectal cancer. Elevated PSA levels or the presence of hidden ("occult") blood in stool samples can prompt a doctor to perform additional tests to confirm a cancer diagnosis.

An abnormal screening result does not automatically mean cancer. Abnormal results can happen for many reasons. Your doctor may recommend follow‑up testing, such as repeating a PSA test or doing a colonoscopy after an abnormal stool test, to understand what’s causing the result.

At diagnosis

Testing for biomarkers as soon as cancer is suspected or confirmed may be a critical first step in your cancer journey. Early testing gives doctors a clearer picture of your cancer’s unique biology, which helps guide treatment decisions.

Knowing your biomarker status upfront can help identify therapies that are more likely to work and help avoid treatments that may be less effective or cause unnecessary side effects. This helps tailor your care plan to your specific cancer from the very beginning.

Also, if you have a solid tumor and tissue is already being removed – such as during an initial surgery or biopsy – doctors can test it for biomarkers at the same time. This allows valuable information to be gathered without needing an additional biopsy. If surgery isn’t part of your care, a separate biopsy may be needed to collect a tumor sample.

Before treatment starts

Getting test results before treatment begins can help open the path to certain targeted therapies, immunotherapies, or clinical trials that require biomarker information upfront.

For example, lung cancer patients with an EGFR mutation are more likely to respond to targeted EGFR inhibitors. Knowing this before treatment starts helps doctors to match patients with therapies that target that mutation.

Monitoring during and after treatment

Biomarkers can be monitored to see how cancer responds to treatment or changes over time. Because some cancers can shift in their biomarker status, retesting helps doctors make sure that the current treatment still matches the cancer’s biology.
For example, in breast cancer, HER2 status can sometimes change—a tumor that was HER2 positive at diagnosis may later become HER2 negative (or vice versa). Retesting helps identify the most appropriate treatments for the cancer’s current biology.
Biomarker testing is also important if cancer comes back or spreads. A recurrence may have different characteristics than the original tumor. Monitoring biomarkers at these stages helps doctors avoid therapies that may no longer be appropriate.