The College of American Pathologists (CAP), American Society for Clinical Pathology (ASCP), and the American Society of Clinical Oncology (ASCO) has issued guidance for HER2 testing in patients with gastroesophageal adenocarcinoma.
Indication: advanced gastroesophageal adenocarcinoma (not surgically resectable) with a good performance status and low cardiac risk who may be candidate for systemic therapy that includes trastuzumab.
Testing: immunohistochemistry (IHC)
Staining: membranous (complete, basolateral or lateral)
Biopsy
Staining
Interpretation
In Situ Hybridization
no reactivity in any cell
IHC 0 (Negative)
do not test
tumor cell cluster (5+ tumor cells) with faint or barely perceptible membranous reactivity
IHC 1+ (Negative)
do not test
tumor cell cluster (5+ tumor cells) with weak to moderate membranous reactivity
IHC 2+ (Equivocal)
perform
tumor cell cluster with strong membranous reactivity
IHC 3+(Positive)
do not test
SurigcalResection
Staining
Interpretation
In Situ Hybridization
no reactivity OR membranous reactivity in less than 10%
IHC 0 (Negative)
do not test
barely perceptible reactivity in >= 10% of tumor cells with cells reactive in only a part of their membranes
IHC 1+ (Negative)
do not test
weak to moderate membranous reactivity in >= 10% of tumor cells
IHC 2+ (Equivocal)
perform
strong membranous reactivity in >= 10% of tumor cells
IHC 3+(Positive)
do not test
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