The number of circulating tumor cells (CTCs) in the blood is a strong predictor of worsening disease in patients with metastatic breast cancer, providing a less costly and less invasive means of such evaluation.

CTCs are associated with poor clinical outcomes in metastatic breast cancer. To validate the prognostic and predictive significance of this biomarker, Minetta Liu, MD, and colleagues analyzed six peer-reviewed, published studies, all of which happened to employ the FDA-approved CellSearch immunomagnetic/immunofluorescence assay. Teams from international cancer centers contributed blinded data to create a pooled data set of 841 patients.

The large sample size allowed the researchers to confirm previous findings linking a CTC count of 5 or higher with disease progression. The predictive value of CTC was not affected by treatment type (chemotherapy, endocrine therapy, biologic therapy) or line (first-line, second-line, or third-line or more); by tumor type (hormone receptor positive/negative, HER2 positive/negative); by presence or absence of bone metastases; or by presence or absence of disease limited to bone.

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“When a patient with metastatic breast cancer feels well and looks well, has had normal recent scans and CTC results that are consistently less than 5, we feel more confident in her current treatment plan and may delay repeat imaging studies in favor of the less-invasive CTC blood test,” explained Liu in a statement describing the findings, which will be presented at the annual meeting of the American Society of Clinical Oncology, to be held June 3-7, 2011, in Chicago, Illinois (