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Some biomarker tests might find gene changes that increase your risk of cancer or other diseases. If you were born with these changes, they are often called inherited or germline mutations.

For example, people with colorectal cancer or endometrial cancer are typically tested for genetic changes such as microsatellite instability (MSI) and defective mismatch repair genes (dMMR).

If such a change is found, the health care team might recommend speaking with a genetic counselor about genetic testing for Lynch syndrome, an inherited condition in which people are at higher risk for several types of cancer. People with this syndrome might benefit from screening for other cancers.

Exposure to viruses

Certain viruses, such as human papillomavirus (HPV) and hepatitis C (HCV), can cause cancer. Testing for viral biomarkers can show if people are at increased risk for developing certain cancers or if the cancer was caused by the virus.

It might also give insight into:

• Treatment options, such as immunotherapy
• Treatment response
• Whether cancer has recurred

Some biomarkers can be used to help find cancer early in people without symptoms or to help diagnose cancer in people who already have signs or symptoms. Although most often, a biopsy is needed to know for sure.

For example,

• Prostate-specific antigen (PSA) is a protein that can often be found at higher levels in the blood of people with prostate cancer. It can help screen for prostate cancer, especially in older men without any symptoms.
• Multi-cancer detection tests check blood or other body fluids for signs of cancer, such as abnormal pieces of DNA, RNA, or proteins.

are often designed to attack cancer cells that have certain gene or protein changes. Biomarker testing before treatment can help show whether these drugs are likely to be helpful.

For example, biomarker testing for EGFR gene changes can show if targeted drugs known as EGFR inhibitors might be helpful in treating the cancer.

Immunotherapy drugs called immune checkpoint inhibitors can often help the body’s immune system attack cancer cells. They can be helpful in treating some cancers, but they don’t work against others.

Some biomarker tests can look for signs that can help predict whether these drugs will be helpful, such as the cancer cells having a high tumor mutational burden (TMB) or damaged DNA mismatch repair (MMR) genes.

Biomarker testing can sometimes be used to see how well treatment is working. These tests may be repeated before, during, and after treatment to see how a cancer is responding to treatment or to watch for early signs of recurrence. 

For example,

• Testing for a gene variant called BCR-ABL in people with chronic myeloid leukemia (CML) shows how many CML cells are present. This can be measured before treatment starts and then be repeated later to see how well the treatment is working.
• A carcinoembryonic antigen (CEA) test in people with colon cancer, might be done prior to and throughout treatment to see if the number declines. This can help show whether the treatment is working.

Some biomarker tests can be used after treatment to look for possible signs of the cancer coming back. Both the PSA blood test in prostate cancer and testing for the BCR-ABL gene in CML are examples of tests that can be used to look for signs of cancer recurrence, often before the person has any symptoms. This might allow treatment of the recurrence to start earlier.

Testing for certain biomarkers may be needed to see if someone is eligible for a clinical trial.

Some biomarker tests can help show if a person might benefit from more treatment, but they don’t specify if a particular treatment would be helpful.

For example, some tests look at patterns of genes or proteins in cancer cells to see if the cancer is more likely to return after the initial treatment. If it is, then further longer or more intense treatment might be useful. If not, a person could avoid more treatment and its possible side effects.