New HER2 testing guidelines

A joint, Focused Update of the "Human Epidermal Growth Factor Receptor 2 (HER2) Testing in Breast Cancer" clinical practice guideline has been developed by an expert panel of pathologists and oncologists and issued by the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) to address new information made available since the guideline's previous update in 2013. Notably, the 2018 Focused Update addresses uncommon clinical scenarios and improves clarity, particularly for infrequent HER2 test results that are of uncertain biologic or clinical significance.

Updated findings of note include:

• Revision of the definition of IHC 2+ (equivocal) to the original FDA-approved criteria.
• Repeat HER2 testing on a surgical specimen if the initially tested core biopsy is negative is no longer stated as mandatory. A new HER2 test may (no longer should) be ordered on the excision specimen on the basis of some criteria (such as tumor grade 3).
• A more rigorous interpretation criteria of the less common patterns that can be seen in about 5% of all cases when HER2 status in breast cancer is evaluated using a dual-probe ISH testing. These cases, described as ISH groups 2 to 4, should now be assessed using a diagnostic approach that includes a concomitant review of the IHC test, which will help the pathologist make a final determination of the tumor specimen as HER2 positive or negative.
• The Expert Panel also preferentially recommends the use of dual-probe instead of single-probe ISH assays, but it recognizes that several single-probe ISH assays have regulatory approval in many parts of the world.

THE COMPLETE FOCUSED UPDATE was published May 30, 2018 as an early online release in Archives of Pathology & Laboratory Medicine.