Past studies have suggested that trastuzumab may benefit breast cancer patients whose tumors overexpress, or produce too much, of the HER2 proteina condition that occurs in 20% to 30% of breast cancer patients. Trastuzumab is a monoclonal antibody that works by targeting the HER2 protein.

To maximize the drugs benefits, participation in trials of trastuzumab have been limited to women who, based on laboratory tests, overexpress HER2 or have an amplified HER2/neu gene, which can also lead to HER2 overexpression. To determine trial eligibility, laboratories use several testing methods, including immunohistochemical analyses such as the FDA-approved DAKO HercepTest (which measures HER2 protein overexpression) and fluorescence in situ hybridization (which measures HER2/neu gene amplification).

In one study, Patrick C. Roche, Ph.D., of the Mayo Clinic and Mayo Foundation in Rochester, Minn., and Edith A. Perez, M.D., of the Mayo Clinic in Jacksonville, Fla., and their coworkers compared results from assays done by local laboratories of 119 patients enrolled in a collaborative trial of the North Central Cancer Treatment Group and the Mayo Clinic with assays performed by a central laboratory.

The authors found that only 74% of the positive local laboratory test results could be confirmed by central testing to have HER2 overexpression and only 66% had confirmed HER2 gene amplification. Of nine tumors reported to have HER2 gene amplification by local testing, only six (67%) could be confirmed by central testing.

"The overall performance of HER2 testing by local laboratories in this initial sample of 119 patients w
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Contact: Linda Wang
jncimedia@oupjournals.org
301-841-1287
Journal of the National Cancer Institute
4-Jun-2002