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Impact of Variation in Test Results

The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) found that approximately 20% of current HER2 testing may be inaccurate.
A study in Newfoundland from 1997-2000 discovered within a group of 1,013 breast cancer patients that up to 383 or more than one third were misdiagnosed as falsely negative when retested. More than 100 of these inaccurately tested and diagnosed patients were deceased by the time the errors were discovered.
False positives are also a concern. Some studies have found that up to 18% of patients could receive HER2-targeted therapy unnecessarily due to false positive results. Thus, exposing them to cardiac risk and unnecessary expense, in the amount of up to $70,000-$100,000 per patient.
The concern over accuracy in HER2 testing precipitated ASCO and CAP to develop guidelines for HER2 testing in 2007 and to create additional regulation and quality control requirements for accredited laboratories performing certain predictive testing. The guidelines have been revised and republished as of 2013.