re than 4 copies of the HER2 gene per tumour cell if no chromosome 17 control is used.
In general, CISH is considered positive if there are more than 5 copies of the HER2 gene per nucleus in greater than 50% of tumour cells.
For full instructions on assay performance and interpretation please refer to the package inserts of validated FISH and CISH assays. Official recommendations on HER2 testing may also apply.
For any other method that may be used for the assessment of HER2 protein or gene expression, the analyses should only be performed by laboratories that provide adequate state-of-the-art performance of validated methods. Such methods must clearly be precise and accurate enough to demonstrate overexpression of HER2 and must be able to distinguish between moderate (congruent with 2+) and strong (congruent with 3+) overexpression of HER2.
Detection of HER2 over expression or HER2 gene amplification in gastric cancer
Only an accurate and validated assay should be used to detect HER2 over expression or HER2 gene amplification. IHC is recommended as the first testing modality and in cases where HER2 gene amplification status is also required, either a silver-enhanced in situ hybridisation (SISH) or a FISH technique must be applied. SISH technology is however, recommended to allow for the parallel eva luation of tumour histology and morphology. To ensure validation of testing procedures and the generation of accurate and reproducible results, HER2 testing must be performed in a laboratory staffed by trained personnel. Full instructions on assay performance and results interpretation should be taken from the product information leaflet provided with the HER2 testing assays used.
In the ToGA (BO18255) trial, patients whose tumours were either IHC3+ or FISH positive were defined as HER2 positive and thus included in the trial. Based on the clinical trial results, the beneficial effects were limited to patients with the highest level of HER2 protein overexpression, defined by a 3+ score by IHC, or a 2+ score by IHC and a positive FISH result.
In a method comparison study (study D008548) a high degree of concordance (> 95%) was observed for SISH and FISH techniques for the detection of HER2 gene amplification in gastric cancer patients.
HER2 over expression should be detected using an immunohistochemistry (IHC)-based assessment of fixed tumour blocks; HER2 gene amplification should be detected using in situ hybridisation using either SISH or FISH on fixed tumour blocks.
The recommended scoring system to eva luate the IHC staining patterns is as stated in table 3:
Table 3 Recommended scoring system to eva luate the IHC staining patterns in gastric cancer
Score
Surgical specimen - staining pattern
Biopsy specimen - staining pattern
HER2 overexpression assessment
0
No reactivity or membranous reactivity in < 10% of tumour cells
No reactivity or membranous reactivity in any tumour cell
Negative
1+
Faint/barely perceptible membranous reactivity in ≥ 10% of tumour cells; cells are reactive only in part of their membrane
Tumour cell cluster with a faint/barely perceptible membranous reactivity irrespective of percentage of tumour cells stained
Negative
2+
Weak to moderate complete, basolateral or lateral membranous reactivity in ≥ 10% of tumour cells
Tumour cell cluster with a weak to moderate complete, basolateral or lateral membranous reactivity irrespective of percentage of tumour cells stained
Equivocal
3+
Strong comple |
