A biomarker is a molecule or other factor in the body that doctors can measure with blood tests or other methods. Doctors use biomarker testing for cancer for several reasons.

For one, doctors use biomarkers to screen for certain common cancers. A familiar example is the PSA test, which detects a biomarker of prostate cancer.

Another reason doctors use biomarkers is to see if you have an increased risk for a certain type of cancer due to genetic changes. One of the best-known cancer biomarkers is the BRCA1 mutation, which increases the risk for breast cancer.

Finally, if you have cancer, biomarker testing can provide information about your tumor, such as whether it’s aggressive. It can also help determine if you’re a candidate for innovative targeted therapies and immunotherapies, or participation in a clinical trial of a new cancer treatment.