Circulating tumor cell (CTC) tests

Circulating tumor cell tests look for proteins or cells that break away from a breast cancer tumor and enter the bloodstream.

The amount of circulating tumor cells (CTCs) in your blood can suggest cancer spread. CTCs can also be a sign that cancer isn’t responding to treatment.

CTCs are biomarkers, or biological markers: signs of disease or changes in the body that can be tested in blood or tissue.

How CTC tests work

CTC tests are a type of liquid biopsy. Liquid biopsies look for cancer cells in a blood sample, rather than in a tumor tissue sample.

For a CTC test, you’ll go to a lab to have a blood sample taken by needle from a vein in your arm. The vein is usually on the inside of your elbow, but sometimes a vein on the wrist or back of the hand is used.

Healthcare professionals can also take a blood sample through a chemotherapy port if you have one. This is a small device placed under the chest skin near a vein so chemo can be delivered.

CTC tests measure the amount of tumor cells in your blood to predict:

• Whether cancer is spreading to another part of the body
• How well a treatment is working to control the cancer

CTC tests are not the same as ctDNA tests:

• CTC tests look for cancer cells that broke away from a tumor.
• ctDNA tests look for pieces of cancer cell DNA, which can confirm genetic mutations that medicines might be able to target.

Who gets CTC tests?

Right now, CTC tests are only available to people with metastatic breast, prostate, or colon cancer. They may also be used if you participate in a clinical trial.

Why are CTC tests important?

CTC tests are useful in monitoring metastatic breast cancer. They help predict when treatments aren’t working well, and if cancer cells are spreading from one site to another.

CTC tests are fairly new to patients. Only one, CellSearch, is FDA-cleared to use outside of research in breast cancer.

Because these tests are so new, experts recommend that doctors use them in combination with other tests to diagnose and monitor metastatic breast cancer. The hope is that the tests will get better as more people use them.

To learn about other tests used in breast cancer, visit the Testing page.