Detecting breast cancer with just a blood sample is the goal of several new tests hitting the market, but experts say it's too early to tell whether using such tests could make a difference in terms of patients' treatment and survival.
One new test, called ClearID Breast Cancer, is marketed for detecting breast-cancer recurrence in women whose cancer is in remission, and also for detecting breast cancer in women at high risk of the disease.
ClearID, manufactured by the cancer-diagnostics company Cynvenio Biosystems, looks for tumor cells circulating in the blood, which the company says could possibly indicate cancer present in the body before it becomes visible on a scan. If the level of these "circulating tumor cells" is above a certain threshold, further tests are done. [6 Foods That May Affect Breast Cancer Risk]
While other tests use levels of circulating tumor cells to monitor breast cancer in some patients already known to have metastatic disease (that has spread to other organs), the makers of ClearID say that their test is more sensitive, and may benefit women who have no symptoms of cancer. But so far, there is no evidence to support this claim.
Experts say the science is exciting, but further studies are needed.
"I see promise in this type of work, but I don't see the evidence of how much difference it really makes," said Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society. It would be premature to say that the test has value in terms of improving patient outcomes, he added.
Breast-cancer blood test
Breast-cancer survivors (women in remission) are typically monitored with a physical exam and a check for symptoms, as well as mammograms every six months to a year. Tests such as CT scans and blood tests for tumor markers (similar to ClearID) are not recommended for women who don't have any symptoms, said Dr. Charles Shapiro, director of breast medical oncology at Ohio State University Comprehensive Cancer Center.
"The issue is whether early detection of these cells makes a difference," Shapiro said, referring to circulating tumor cells. "And I don't know whether it does or not."
Dr. Lee Schwartzberg, a scientific adviser at Cynvenio Biosystems, acknowledged that the company does not yet have evidence of whether the company's test is helpful for asymptomatic patients — studies of that question need to be completed. Instead the test is marketed as a way to provide peace of mind for patients.
"For people who are interested in monitoring, this represents an opportunity to look for [cancer recurrence]," Schwartzberg said. "But the formal tests to prove that the long-term outcome is better are being conducted now."
A negative result on ClearID does not mean that a patient is cancer-free, according to the company's website. Instead, if levels of circulating tumor cells remain low, "it likely indicates a lack of tumor progression, or response to therapy."
Previous studies have found that patients with metastatic disease who have more circulating tumor cells after a round of chemotherapy tend to do worse than patients with fewer circulating tumor cells, Shapiro said. And a study published last year found that women with nonmetastatic breast cancer who had higher levels of circulating tumor cells were more likely to progress to the metastatic stage, and to die from the disease over an eight-year period.
But studies still need to be conducted to see whether treating women after detecting circulating tumor cells improves their survival, Shapiro said.
Another company, called Matrix-Bio, is also working on blood tests for breast cancer. One test for cancer recurrence, called VeraMarker, looks for small molecules, or biomarkers, in the blood. It has been licensed to Quest Diagnostics but is not currently available to physicians or patients.
Matrix-Bio is currently working on studies to demonstrate that the test works, and is pursuing approval from the U.S. Food and Drug Administration (FDA), according to Matrix-Bio's website. The company also has other tests in its pipeline, aimed at detecting breast cancer in its early stages, or its recurrence.
ClearID does not have FDA approval, but it doesn't need it. While the FDA regulates drugs and test kits, it does not have oversight over tests performed only in a single laboratory, as ClearID is, Lichtenfeld said. Although the lab is certified, this certification indicates only that the lab practices are up to standards, not that the claims of the test are valid, Lichtenfeld said.
"They can make claims that the test does something, and it has to be taken at face value," Lichtenfeld said.
While ClearID and VeraMarker still need more scientific study, experts say the idea of monitoring cancer with just a blood test is what scientists hope to do in the future.
"In medicine, it's the direction in which we're trying to go," said Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York. "We need to be able to detect cancers…at a point when they would, hopefully, be theoretically curable," Bernik said.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.