ScienceDaily (Jan. 8, 2009) — An antibody-based test that is used to detect circulating breast cancer cells and provide prognostic information for patients during treatment may not detect all subtypes of breast cancer.

Researchers have identified five subtypes of breast cancer by their gene expression patterns. The subtypes – basal, HER2-positive, luminal A and B, and normal-like – vary in their natural history and response to therapy. CellSearch is an antibody-based test, approved by the U.S. Food and Drug Administration, to detect circulating breast cancer cells in patients before and during treatment. Previous studies suggest that women who have a decrease in circulating tumor cells after the start of treatment are likely to have a better outcome than those who do not have a decline. It was not known if the CellSearch assay detected all five subtypes of cancer equally.

In the current study, Anieta Sieuwerts, Ph.D., of the Erasmus Medical Center in Rotterdam, The Netherlands, and colleagues tested whether the assay could isolate cells of breast cancer cell lines whose subtype is known that had been added to human blood from a healthy volunteer. The investigators tested cells from a total of 34 cell lines that represented a mix of the five breast cancer subtypes.

The assay did not detect the nine normal-like breast cancer cells but did detect the other subtypes. "New tests that include antibodies that specifically recognize normal-like breast tumor cells…are needed," the authors conclude.

This research is published in the December 30 issue of the Journal of the National Cancer Institute.

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