When results were negative with IHC and FISH, they were also generally negative with Oncotype.
But all 23 equivocal results as reported by IHC and FISH came out negative with Oncotype, the investigators found.
Only 28 percent of positive IHC and FISH results also came up positive with the Oncotype, while 33 percent came out as equivocal and 39 percent as negative.
"Anyone who has had this test performed needs to make sure that their hormone-receptor analyses were done by other FDA-approved methods and not rely upon this test alone," said Dabbs.
Overall, though, only a small proportion of tumors among the 843 women were HER2-positive, noted Goldstein, which could have biased the results.
And, in a statement provided to HealthDay, Genomic Health disagreed with the findings, proposing that the "conclusions appear to be one-sided" and require additional data.
The discordances between tests are "not uncommon" and because of those discrepancies the company began including RT-PCR measurement of HER2 in Oncotype "with the goal of providing added clarity in cases where HER2 results by IHC and FISH are uncertain or conflicting," according to the statement.
HER2 status "should be assessed in all patients by IHC and/or FISH," the company also stated.
A 2010 study funded by Genomic Health found that RT-PCR results actually did agree with FISH results.
The U.S. National Library of Medicine has more on breast cancer.
SOURCES: David J. Dabbs, M.D., professor and chief, pathology, Magee-Womens Hospital, University of Pittsburgh Medical Center; Lori J. Goldstein, M.D., director, Breast Evaluation
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