With recent advances in molecular technology, in the future your doctor may order a blood test for Circulating Tumor Cells (CTCs) to aid cancer care and cancer treatments.
What are CTCs?
Circulating tumor cells are cancer cells that detach from a primary tumor (for example breast cancer) and travel in the bloodstream to circulate around the body. Some of these cells have the potential to deposit and grow cancer in other organs (for example the liver), known as metastases. Fortunately not all CTCs have this ability and may remain inactive (dormant), or be suppressed by the immune systems to prevent a cancer returning (1).
Why are CTC’s considered important?
CTC are considered important because one of the challenges of treating cancer is that despite using surgery, chemotherapy and radiation to remove all known traces, there is still a risk of the cancer returning which may be a result of CTC’s.
Detection and specific numbers of CTC’s can then help doctors decide which patients are more at risk of recurrence of cancer and more likely to benefit from additional cancer treatments.
(In multiple clinical trials, the number of CTCs was a significant independent predictor of prognosis in patients with metastatic breast (2, 3), colorectal (4), or prostate (5) cancer).
CTCs concentrations may also serve as a marker of how well the patient is responding to treatment, and in the future may also provide a ‘liquid biopsy’, or way to sample tumor cells without needing to form a more invasive needle biopsy. This would be highly useful, especially for cancers that are hard to reach, or that may pose a risk to the patient’s safety such as a liver biopsy that may result in internal bleeding.
CTC Testing. Interestingly, circulating tumour cells were seen and documented in blood samples under the microscope in Australia in 1869 (6). Today, the most widely used cytometric CTC technology currently in clinical testing is the CellSearch™ system (Veridex LLC, Huntingdon Valley, PA, USA) and is the only technology to have received FDA approval for the enumeration of CTC in whole blood for specific groups of cancer patients. The major advantage of this system is its proven reproducibility, reliability, sensitivity, and accuracy(7,8), which are features crucial to any biomarker technology to ensure validity of results in clinical testing.
Although this test is not intended to replace imaging or cancer markers currently used in treatment, recent research has shown that CTC testing may predict treatment responses earlier than when compared with imaging (in patients with metastatic breast cancer(2,9), and earlier than with measuring prostate specific antigen (PSA) levels used to evaluate metastatic prostate cancer (5).
For whom can the test be currently used?
At this time, CTCs are not widely measured in clinical practice, however in the future appears promising to be used for diagnosis and prediction of metastatic cancers, follow-up after curative treatment, stratification for adjuvant therapies, and detection of response to treatment. And, as cancer treatment becomes more focused on targeted detection and therapies, it will be highly valuable to have a way of doing this by looking in the blood.
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Feature Image by Penny and Annie