Her2 Testing in Gastric Cancer
Key facts
- HER2 gene amplification and protein over-expression occurs in a
significant proportion of gastric cancers
- HerceptinTM is licensed for the treatment of
metastatic and locally advanced gastric cancer and adenocarcinoma
of the gastro-oesophageal junction
- HER2 testing is a pre-requisite for prescribing of
HerceptinTM
Over-expression of the membrane-associated receptor protein HER2
(erbB-2), as a consequence of gene amplification, occurs in 7%-27%
of gastric cancers.
The EMEA has recently licensed the HER2-targeted antibody
trastuzu-mab (HerceptinTM) for the treatment of
metastatic and locally advanced gastric cancer and adenocarcinoma
of the gastro-oesophageal junction. Patients achieving an IHC score
of 3+, or who are 2+ by IHC and HER2-amplified by in situ
hybridisation are considered eligible for Herceptin treatment.
Source Bioscience offers the FDA-approved, standardised and
validated Ventana PATHWAY™ immunohistochemistry test for HER2
protein expression, coupled with the new Ventana BDISH (Brightfield
Dual-Colour In Situ Hybridisation) test for confirming
HER2 gene status, both run on the Ventana BenchMark™ XT slide
processing system.
Evaluation
Specimens immunostained for HER2 protein are assessed visually
by a registered pathologist, with specialised training in the
scoring of gastric cancers, who will assign a score of 0 to 3+; a
score of 3+ is regarded as positive for HER2 protein
over-expression, and indicative of HER2 gene amplification. Scores
of 0 and 1+ are considered negative. Specimens achieving a score of
2+ are considered borderline, and are referred for BDISH HER2 gene
analysis. BDISH scores are expressed as ratios of HER2 gene copy
number to copy number of chromosome 17. A score greater than 2 is
considered evidence of HER2 amplification.
Examples of immunostaining for HER2 protein (top), and BDISH
detection of the HER2 gene (bottom) in gastric tumours amplified
for HER2