Recent Breast Cancer HER2 Testing Guideline Update Produces Similar Positivity Rate

Updates to the 2013 human epidermal growth factor receptor 2 (HER2) testing guideline in breast cancer did not affect the overall positivity rate or the proportion of patients eligible for targeted therapy, according to a comparative analysis published in the Journal of Clinical Oncology (published online April 26, 2017; doi:10.1200/JCO.2016.70.5319).

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The American Society of Clinical Oncology and the College of American Pathologists originally released a guideline for HER2 testing in breast cancer in 2007. Since then, an update was provided in 2013 that focused on identification of patients who may benefit from HER2-targeted therapy as well as limitation of false-negative results. The update further included new parameters for immunohistochemistry (IHC) 3+ scores and cutoffs in situ hybridization-positive and equivocal results.

Wedad M Hanna, MBBCh, Sunnybrook Health Sciences Centre (Toronto, Canada), and colleagues studied the effects of the 2013 updates for HER2 testing in breast cancer on testing patterns and interpretation. Researchers compared patients tested during 2012 (n = 2201) and 2014 (n = 2558) to evaluate how the guideline affected HER2 testing positivity before and after the update.

Researchers found that though the number of samples tested increased from 2012 to 2014, HER2 positivity remained constant (15.7% vs 15.5%, respectively).

Additionally, the number of repeat tests performed within a 6-month range more than doubled, with 122 performed in the 2012 cohort (5.5%) and 302 in the 2014 cohort (11.8%). There were more patient cases with equivocal HER2 status after the update (4 in 2012, 90 in 2014).

Fewer IHC 2+ tumors were reported after the update (25.3% in 2012, 20.3% in 2014), but IHC 3+ tumor observations were similar between the cohorts (11.8% vs 11.5%, respectively).

Researchers wrote that “the benefit of targeted therapy in the equivocal group in not proven, so targeted therapy should not be considered for patients in this category.” They further concluded that limitation of the number of patient cases in such category should be refined in future guideline updates.—Zachary Bessette