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BookmarkScienceDaily (May 20, 2008) — With the goal of tailoring cancer treatment for each individual, researchers at Georgetown University Medical Center today presented a study suggesting a simple blood test can help doctors more reliably assess treatment efficacy for patients with metastatic breast cancer.
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"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," says Minetta Liu, M.D., of Georgetown's Lombardi Comprehensive Cancer Center. "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."
Using the FDA-approved CellSearch™ technology, researchers measured the number of circulating tumor cells (CTC) in blood collected from women with metastatic breast cancer. About one tablespoon of blood was collected every three to four weeks. The number of CTCs was correlated with disease response or progression as determined by standard radiology studies performed every 9-12 weeks. The women in the study received various treatments including chemotherapy, endocrine therapy, and combination therapy with a biologic agent.
A CTC count of five was used as the threshold, based on previous studies. There was a highly significant difference in the distribution of progression between two groups of patients defined by their CTC result. Seventy-one percent of patients who had a CTC greater than or equal to five had disease progression, and 66 percent of patients with a CTC count of less than five did not.
"A CTC count of five or greater at the time of restaging was associated with a 5.32 fold increase in a patient's chance of having disease progression compared to CTC counts of less than five," explains Liu. "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."
Liu adds that the CTC assay is a more reliable means of assessing treatment response than the traditional tumor markers currently in use.
"We have a follow-up study underway that evaluates CTC results within the framework of a randomized clinical trial to eliminate potential variability from the treatment administered, "says Liu, the national principal investigator of the new trial. Liu and her colleagues believe a study with the same therapies would offer even stronger evidence for routine use of CTC in patients with metastatic breast cancer.
"We have many treatment options for advanced breast cancer. The key is to find the most effective therapy for each patient. It shouldn't take months to figure that out," she concludes.
The study was funded by Veridex, LLC, makers of CellSearch. Liu reports receiving limited compensation for research-related speaking engagements on behalf of Veridex.
Liu's preliminary results were released online in advance of the American Society of Clinical Oncology annual meeting. The complete data will be presented during the poster discussion of this study at the annual meeting place in Chicago May 30-June 3.
