And it's far from clear that this simple blood test would be a good replacement for imaging to track the progress of the cancer, he added.
Nor do CTCs tell you which treatment may be best, like certain other markers, including HER2/neu and estrogen-receptor status, added Armstrong, although he said it might indicate the need for a more aggressive approach.
Still, Armstrong said, "these CTCs are likely to become very important because they're not just a protein. They're the actual cancer cell, so if you can isolate them and measure things that have gone wrong inside the cancer cell, you could eventually use them to guide therapy for an individual. [And] you could monitor it over time especially to assess response to treatment and modify treatment [if necessary]. Cancer cells mutate and can develop abnormalities that can be an Achilles' heel for drugs. Without that information, it's very hard to guide therapy."
Other studies being presented at the symposium confirm the potential importance of CTC levels in predicting the odds for a recurrence, or a patient's general prognosis after treatment.
One report, from German researchers, found that the presence of only a few CTCs in the blood -- this time, involving early-stage patients -- roughly doubled the risk for a recurrence and death. Five or more of the tumor cells increased the chances of a relapse by 400 percent and death by 300 percent.
A study from scientists at the M.D. Anderson Cancer Center at the University of Texas found that metastatic breast cancer patients who had both chemotherapy and transplants of their own stem cells and had CTCs in their blood also tended to fare badly.
The stem cells may be responsible by carrying CTCs from the bone marrow into the b
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