4
Highlights
ISH Testing
➤ ISH test is rejected and repeated if:
• Controls are not as expected
• Observer cannot find and count at least two areas of invasive tumor
• >25% of signals are unscorable due to weak signals
• >10% of signals occur over cytoplasm
• Nuclear resolution is poor
• Autofluorescence is strong
Report HER2 test result as Indeterminate as per parameters
described.
➤ The pathologist should scan the entire ISH slide prior to counting
at least 20 cells or use IHC to define the areas of potential HER2
amplification.
If there is a second population of cells with increased HER2 signals/cell and this cell
population consists of more than 10% of tumor cells on the slide (defined by image
analysis or visual estimation of the ISH or IHC slide), a separate counting of at least 20
nonoverlapping cells must also be performed within this cell population and reported.
Acceptable (IHC and ISH) Tests
Should preferentially use an FDA-approved IHC, brightfield ISH, or FISH
assay.
➤ IHC rejection criteria:
• Test is rejected and repeated or tested by FISH if:
▶ Controls are not as expected
▶ Artifacts involve most of sample
▶ Sample has strong membrane staining of normal breast ducts (internal
controls)
➤ IHC interpretation criteria:
• Should interpret IHC test using a threshold of more than 10% of tumor cells
that must show homogeneous, dark circumferential (chicken wire) pattern to call
result 3+, HER2 positive.
Reporting Requirements For All Assay Types
➤ Report must include guideline-detailed elements except for changes
to reporting requirement and algorithms defined in this table.
