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.

Guideline Tools & Resources


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HER2 Tissue Donations

Donate laboratory tissue samples for the CAP proficiency testing programs. Contact the Purchasing team at mpspurc@cap.org.

Accreditation Requirements and Proficiency Testing (PT)

Accreditation checklist requirements regarding HER2 assay validation, specimen fixation, proficiency testing, and use of the ASCO/CAP scoring criteria for reporting results are included in the anatomic pathology (ANP), cytogenetics (CYG), and molecular pathology (MOL) checklists.

CAP accredited laboratories may access these checklists through e-LAB Solutions Suite

Non-CAP accredited laboratories may purchase these checklists through the order form.

Meet PT requirements by ordering the appropriate HER2 PT program. Call the CAP customer contact center at 1-800-323-4040 option 1#.

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Guideline status: Active

Originally published: January 2007

Update published: February 2014

Focused Update published online ahead of print: May 30, 2018