Breast Tumor Biomarker Tests Reveal Different Results

The tests for the Human Epidermal growth factor Receptor 2 (HER2) proteins and genes in tissue samples give equivocal results when more than one sample is tested.

The reliability of immunohistochemistry tests for the HER2 protein and fluorescence in situ hybridization, or FISH tests for the HER2 gene have been studied since 2001 and their appears to be some variation in the overall results.

Scientists from the Mayo Cancer Clinic Center, (Jackson, FL, USA) have studies whether teams of pathologists are in concordance when examining the results from these tests. Three teams of pathologists conducted a blinded review of samples from 389 patients who had been enrolled in three adjuvant clinical trials in which HER2 testing was performed by local and central laboratories to determine if patients were candidates for these studies. Each of the three central laboratories received at least six slides from a patient's tumor block that the laboratory used to retest HER2 gene and protein levels.

The pathologists were from central laboratories at the Mayo Clinic, the University of Southern California, (Los Angeles, CA, USA), and the University of Pittsburgh, (Pittsburgh, PA, USA). They found significant heterogeneity, or variability, between two tumor blocks taken from the same patient in 5% to 10% of cases. Most often, one tumor block showed a normal HER2 expression, while the second piece of tumor tested HER2 positive. They found that there was 92% agreement between the immunoassay and the FISH test. In 125 patients from the group of 389, who had more than one tumor block available for analysis they found that 5% to 10% of these samples had dissimilar protein and gene test results.

Edith Perez, MD, deputy director of Mayo Clinic Cancer Center, said, "It is necessary for oncologists to continue to refine these tests and their analysis. That may mean some tests may be needed for multiple tumor blocks, or that pathologists may need to discuss borderline results for some patients.” The findings were presented at the 33rd Annual San Antonio Breast Cancer Symposium held December 8-12, 2010 in San Antonio, TX, USA

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Mayo Cancer Clinic Center
University of Southern California
University of Pittsburgh