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ASCO, CAP Update HER2 Breast Cancer Testing Clinical Practice Guidelines

NEW YORK (360Dx) – The American Society of Clinical Oncology and the College of American Pathologists have updated their guidelines for human epidermal growth factor receptor 2 (HER2) testing in breast cancer. The guidelines, first released in 2007, were last updated in 2013.

The updated guidelines confirm that HER2 gene amplification assessed by in situ hybridization and protein overexpression assessed by immunohistochemistry remain the primary predictors of responsiveness to HER2-targeted therapies in breast cancer. The guidelines also confirmed a lack of benefit from adjuvant trastuzumab for patients whose tumors lack gene amplification and are IHC 1+ or 2+, supporting current overall HER2 testing algorithms.

The HER2 testing panel sought to answer three clinical guideline questions related to HER2 testing. For the first question, which asked for the most appropriate definition of IHC 2+, the new revised definition of IHC 2+ provided by the recommendations is, "invasive breast cancer with weak to moderate complete membrane staining observed in > 10 percent of tumor cells."

The second clinical guideline question asked whether HER2 testing must be repeated on a surgical specimen if initially there is a negative test on a core biopsy. The updated guidelines state that if the initial HER2 test result in a core needle biopsy specimen of a primary breast cancer is negative, a new HER2 test "may be ordered or the excision specimen."

The third question asked for the optimal algorithm for less common patterns observed when performing dual-probe ISH testing in breast cancer. The guidelines provided algorithms for multiple less common patterns.

The guideline update summary was published in the Journal of Clinical Oncology, online June 19.