HER2 IHC Summary
**Note 1:** This SSDI is no longer required by any of the standard setters starting with 2021 diagnoses.
* For cases diagnosed 2021+, this SSDI may be left blank
**Note 2:** Physician statement of HER2 IHC Summary can be used to code this data item when no other information is available.
**Note 3:** The HER2 IHC test performed on the primary breast tissue is to be recorded in this data item.
**Note 4:** Results from nodal or metastatic tissue may be used, **ONLY** when there is no evidence of primary tumor.
**Note 5:** In cases where there are invasive and in situ components and HER2 IHC is done on both, ignore the in situ results.
* If HER2 IHC is positive on an in situ component and HER2 IHC is negative on all tested invasive components, code HER2 IHC as negative (code 0)
* If in situ and invasive components present and HER2 IHC only done on the in situ component, code unknown (code 9)
**Note 6:** In cases where there is a single tumor with multiple biopsies and/or surgical resection with different HER2 IHC results.
* Use the highest (positive versus negative)
**Note 7:** In cases where there are multiple tumors with different HER2 IHC results, code the results from the largest tumor size (determined either clinically or pathologically) when multiple tumors are present.
* Do not use specimen size to determine the largest tumor size
**Note 8:** If neoadjuvant therapy is given, record the assay from tumor specimens prior to neoadjuvant therapy.
* If neoadjuvant therapy is given and there are no HER2 IHC results from pre-treatment specimens, report the findings from post-treatment specimens
**Note 9:** A 2+ (equivocal) finding by IHC should result in additional testing with ISH to determine gene copy number.
**Note 10:** An immunohistochemistry (IHC) test identifies the protein expressed by the gene (ERBB2), and an in situ hybridization (ISH) test identifies the number of copies of the gene (ERBB2) itself.
**Note 11:** HER2 is not routinely done on pure in situ tumors (behavior /2); however, if you have an in situ tumor and there are HER2 results, go ahead and record it. Otherwise code 9.