HER2 Testing in Breast Cancer

Target Population: Oncologists, pathologists

Background and Objective

The ASCO/CAP committee has updated its 2007 recommendations for human epidermal growth factor receptor 2 (HER2) testing in breast cancer patients to improve the accuracy and utility of predicting treatment response.

Key Recommendations to Oncologists

• Require HER2 testing of all primary breast cancers; test at a metastatic site if stage IV disease. Repeat testing in patients with tumors exhibiting clinical-pathological behavior suggestive of HER2-positive disease, even if previous tests indicated HER2-negative disease.

• If the initial HER2 test result is equivocal, perform reflex testing with an alternative HER2 test on the same specimen or an alternative specimen.

• If the HER2 test result is positive, anti-HER2 therapy should be recommended. If the result is negative and no clinical features are discordant with HER2 testing, anti-HER2 therapy should not be recommended.

• If reflex testing with an alternative assay continues to provide an equivocal result, the oncologist may, on a case-by-case basis, still consider anti-HER2 testing.

Key Recommendations to Pathologists

• Using an assay that has been FDA approved is preferable; a lab certified by Clinical Laboratory Improvements Amendments regulations can develop its own test, but the test must be prospectively validated in the same lab that will use it, and its analytic validity must be documented according to CAP guidelines.

• Criteria for reporting HER2 test results as positive, negative, equivocal, or indeterminate using immunohistochemistry or in situ hybridization methods are stipulated by CAP guidelines and detailed in the update.