Patient selection: invasive breast carcinoma
Testing: validated dual-probe ISH assay (to HER2 and CEP17)
Requirements for interpretation:
(1) interpretation of the invasive component of the tumor
(2) controls (batch, on-slide) show appropriate hybridization
Parameters:
(1) HER2 to CEP17 ratio
(2) average HER2 copy number in signals per cell
|
HER2/CEP17 Ratio
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HER2 Copy Number
|
Interpretation
|
|
>= 2
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>= 4
|
positive
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|
>= 2
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< 4
|
positive (rare pattern)
|
|
< 2
|
>= 6
|
positive
|
|
< 2
|
4 to 5.99
|
equivocal
|
|
< 2
|
< 4
|
negative
|
Expressed as rules:
(1) HER2 is positive if either the ratio is >= 2 OR copy number is >= 6.
(2) HER2 is negative if ratio is < 2 AND copy number < 4.
(3) HER2 is equivocal if not positive or negative.
Results that do not fit into the above schema are rare and categorized as equivocal.
Equivocal results should have reflex testing using one of the following:
(1) immunohistochemistry on the same specimen
(2) ISH with an alternative chromosome 17 probe
(3) immunohistochemistry or ISH on a new specimen (or different block)
If there is a second contiguous population of cells with increased HER2 signals per cell:then:
(1) Determine what percent of the total tumor that this fraction represents.
(2) If the population represents > 10%, then evaluate ISH in at least 20 nonoverlapping cells from this population separately.
(3) Report the results of the 2 populations separately.
