Over the last decade, the medical community has made significant strides in detecting and treating breast cancer, but mortality rates for the disease remain high. It is still the second leading cause of death in U.S. women. Consequently, doctors are constantly looking for new tools that can help them better manage the disease and prolong patients’ lives. A new test that measures circulating tumor cells (CTCs) can potentially help doctors do this by allowing them to more accurately predict both progression-free survival and overall survival in women with metastatic breast cancer. Being able to predict survival not only helps doctors choose the best course of therapy, but also keeps patients better informed about their progress in fighting the disease.

CTCs—cancer cells that have detached from solid tumors and have entered the bloodstream—are a mechanism through which cancer spreads to other parts of the body. Once in the blood, CTCs may take root in another tissue or organ, enabling what was once a localized cancer to spread. Rare in healthy individuals and patients with nonmalignant diseases, CTCs have been shown to be present not only in breast cancer patients, but in individuals with a variety of metastatic cancers. Clinical trial data submitted to the FDA, however, focused on the CTC test’s use in predicting survival in metastatic breast cancer patients, and therefore, the test is currently only approved for that purpose

Laboratories perform the CTC test by taking a blood sample from a patient and mixing it with iron particles that are coated with an antibody that attaches to cells like those found in breast tissue. These particles target CTCs and allow them to be captured with a powerful magnetic field so they can be easily identified and counted. A CTC count of 5 or more has been shown to be predictive of shorter progression-free survival and overall survival in metastatic breast cancer patients at baseline (before starting a new therapy) and first follow-up. However, if a patient’s CTC count is more than 5 at baseline and decreases to less than 5 at first follow-up, survival rates are similar to those who initially had CTC rates less than 5. Consequently, doctors can potentially use the CTC test to set therapeutic goals for patients or to determine earlier if certain therapies are not working.

Currently, the test is indicated for use in patients with metastatic breast cancer, prior to a new course of therapy and at follow-up, but is not recommended as a screening test for any type of cancer. Since the CTC test is new to the market, more studies are needed to help define the test’s limitations and possibilities, and patients should consult their doctors to find out if the test is appropriate for them.

Sources
2004 Breast Cancer Statistics from the American Cancer Society

Cristofanilli M, Budd T, Ellis M, et al. Circulating tumor cells, disease progression, and survival in metastatic breast cancer. N Engl J Med. August 19, 2004;351:781-791. Abstract available online

Cellsearch Test Information from Veridex