Fast Five Quiz: HER2+ Breast Cancer

Pavani Chalasani, MD, MPH


August 23, 2022

Figure 2. FISH test on breast cancer tissue.

Several methods for HER2 testing have been developed; however, approximately 20% of current HER2 testing may be inaccurate, per Markman and colleagues. The American Society of Clinical Oncology (ASCO) and the College of American Pathologists have issued a clinical practice guideline and a focused update to safeguard the accuracy of HER2 testing.

HER2 testing by FISH is usually considered more reliable than by IHC assay; however, FISH is a costlier option. In 15% of invasive breast cancers, equivocal IHC results are seen, whereas equivocal FISH results are seen in < 3% of invasive breast cancer specimens and those that had previously been considered HER2+. Sole reliance on FISH testing for determining HER2 status is becoming increasingly common in some centers.

Learn more about testing for HER2 status in breast cancer.


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