False negative results found in prognostic testing for breast cancer

June 23, 2014

A recent study evaluating HER2 testing in a large cohort of women with breast cancer found important limitations in the conventional way HER2 testing is performed in the United States and internationally. Dartmouth-Hitchcock Norris Cotton Cancer Center physicians and researchers retested tumor samples from a large group of women and found that 22 of 530 women had their tumor type incorrectly classified. The findings were published recently in the journal Cancer.

Breast cancer is categorized into several subtypes based on conventional laboratory and newer molecular tests. This study looked at the accuracy in classifying breast cancers in one particular subtype, specifically those that are “human epidermal growth factor receptor 2” or HER2 positive. When a woman’s cancer tests positive for HER2, targeted therapies are extremely effective in improving outcome and preventing recurrence of cancer.

“We, and other groups, have previously shown that a certain percentage of cases found to be HER2 positive in local laboratories are in fact HER2 negative when tested in central labs. There has, however, been almost no research evaluating the accuracy of a negative HER2 result,” says Peter A. Kaufman, MD, study co-author. “This is the first large study to look at this. What is comforting is that we found that re-testing in larger labs confirmed the original local lab results in the majority of cases.”

Kaufman notes that his team did find that about 4% of cases originally determined to be HER2 negative were in fact HER2 positive on repeat testing. Many of these cases were detected as being positive by testing for HER2 using both of two different and complementary tests (FISH and IHC).The variance in accuracy may be related to how tests are conducted in smaller versus larger pathology laboratories. Read the article.

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