Researchers found that there was 92 percent agreement between the two tests.
Then, the pathologists met face to face to discuss the 8 percent of tumor samples that they did not initially agree on, and reached consensus on 96 percent of the HER2 protein tests and 97 percent of the gene tests. The disagreement most often occurred in HER2 tests that were borderline for the established threshold of HER2+ positivity, Dr. Perez says.
They then looked at 125 patients (in the group of 389) who had more than one tumor block available for analysis. They found that 5 to 10 percent of these samples had dissimilar protein and gene test results.
This variability was greater than suspected, she says. "Some people have reported heterogeneity to be only 1 percent."
The slices from a tumor that make up a tumor block are made very close to each other (a distance of 6 microns) and a second tumor block can be made in the same tumor but at a distance from the original tumor slice. Biological variability can exist within a tumor for a number of reasons, Dr. Perez says. "The stroma surrounding a tumor can have a different impact on growth proteins that are expressed in one part of a tumor, compared to another, and development of pathways that lead to HER2-positivity may not occur at the same time in a tumor."
Finally, the researchers looked at how patients with these dissimilar tumor blocks were treated. In most cases, these patients had been diagnosed as HER2 normal, but the second tumor block tested as HER2+. "These patients may not have been diagnosed correctly and that is a big issue," says Dr. Perez. "It suggests that when a second tumor block is available in patients who test normal, it could be tested to validate these results."
This finding helps explain why some breast cancer patients who
|Contact: Nicole Engler|