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Your doctor may order a test for circulating tumor cells (CTCs) to help guide your cancer care.
What Are CTCs?
One of the major challenges in treating cancer is getting “all” of the cancer, including the parts we cannot see. Even if surgery, chemotherapy, or radiation removes all traces of known cancer, there is still a risk of the cancer returning, often in a distant location in the body. This may occur as a result of CTCs.
Circulating tumor cells were first found in the blood under the microscope nearly 150 years ago. They are cancer cells from the primary tumor that escaped into the bloodstream to circulate around the body. As a result, these cells can serve as seeds for new areas of cancer to grow in distant organs. This is known as metastasis.
Not all CTCs have the ability to land and establish a new metastasis in a distant organ; some may remain dormant (inactive) or be controlled by the immune system for years, sometimes forever.
The Challenge of Finding CTCs
Research and clinical applications for CTCs have grown over the past couple of decades. When CTCs are present in the blood, their concentration is very low: as few as 1 CTC per 1 billion red blood cells. A new technique developed in the last few years allows for CTCs to be bound by surface receptors on the cancer cell to antibodies attached to magnetic nanoparticles that can then be separated, counted, and studied further.
Why Is It Important to Find and Measure CTCs?
Detection of CTCs can help doctors decide which patients are most likely to benefit from additional cancer treatments. The presence of CTCs at concentrations above specific levels using a specific test called Cellsearch (Janssen Diagnostics LLC) is associated with poorer outcomes in patients with colon, breast, and prostate cancer.
The concentration of CTCs in blood may change over the course of treatment. This may serve as a marker of how well a patient is responding to treatment, in addition to (or instead of) using imaging techniques. A declining CTC count during treatment means the treatment is working well, while a rising CTC count may lead to a decision to change to a different treatment.
Measuring CTCs may also provide a liquid biopsy, a way to sample tumor cells without needing to perform a more invasive needle biopsy. This may be especially useful for cancers that are harder to reach and sample safely. A sampling of CTCs may also include a range of cancer cells, while a needle biopsy can only get a single area of a specific tumor.
Current Use and Future Directions
At this time, CTCs are not widely measured in clinical practice. It is still challenging to reliably detect CTCs. However, as cancer treatment becomes more focused on finding specific mutations in cancer cells for targeted therapies, and on noting changes in these mutations over time, it will be very valuable to have a noninvasive way of collecting cancer cells by looking in the blood.
Global Resource for Advancing Cancer Educationhttp://cancergrace.org/cancer-101/tag/circulating-tumor-cells/
To find this and other JAMA Oncology Patient Pages, go to the Patient Page link on the JAMA Oncology website at http://www.jamaoncology.com.
Published Online: May 21, 2015. doi:10.1001/jamaoncol.2015.0711.
Conflict of Interest Disclosures: None reported.
Source: Ashworth TR. A case of cancer in which cells similar to those in the tumors were seen in the blood after death. Austral Med J. 1869;14:146-147.
West H, Jin JO. Circulating Tumor Cells. JAMA Oncol. 2015;1(3):394. doi:10.1001/jamaoncol.2015.0711
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