Dr. Minetta Liu of Georgetown's Lombardi Comprehensive Cancer Center and colleagues compared circulating tumor cells measured from blood taken every three to four weeks from women with metastatic breast cancer. They found a correlation with disease progression shown by radiology studies taken every nine to 12 weeks.

Seventy-one percent of patients who had circulating tumor cells greater than or equal to five had disease progression, and 66 percent of patients with a circulating tumor cells count of less than five did not.

"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," Liu says in a statement. "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."

The study findings are scheduled to be presented by American Society of Clinical Oncology annual meeting in Chicago May 30 to June 3.