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FRIDAY, May 16 (HealthDay News) -- A simple blood test to check levels of circulating tumor cells can help doctors more accurately assess how well treatments are working in women with metastatic breast cancer, according to a Georgetown University Medical Center study.

"It can take several weeks, and sometimes months, to determine if a particular cancer treatment is working, because it can take that long to observe any significant radiographic changes in tumor size or appearance," principal investigator Dr. Minetta Liu, of Georgetown's Lombardi Comprehensive Cancer Center, said in a prepared statement.

"Right now, we have to rely on radiology studies such as CT scans, ultrasound, and the like to determine whether or not there is disease progression. With this new blood test, we have another reliable tool that may allow us to determine much sooner if a therapy is ineffective, so that we can change therapy earlier and potentially make more significant improvements in survival," Liu explained.

In this study, Liu and colleagues measured the number of circulating tumor cells (CTC) in blood samples collected from metastatic breast cancer patients every three to four weeks. The women were receiving various treatments, including chemotherapy, endocrine therapy, and combination therapy with a biologic agent.

The researchers found that 71 percent of patients with a CTC count of five or greater had disease progression, compared with 66 percent of patients with a CTC count of less than five.

"A CTC count of five or greater at the time of restaging was associated with a 5.32-fold increase in a patient's chances of having disease progression compared to CTC counts of less than five," Liu said. "CTC assessments should be used as a surrogate marker for treatment efficacy and disease responsiveness. Changes in CTC results from less than five to greater than or equal to five over time may herald disease progression."

The findings were released online May 15 in advance of the annual meeting of the American Society of Clinical Oncology, in Chicago.

The study was funded by Veridex, LLC, which makes the technology used in this study to measure CTC levels. Liu has received payments from Veridex for speaking engagements.

More information

The U.S. National Cancer Institute has more about breast cancer treatment.