The Human Epidermal Growth Factor Receptor 2 (HER2) is a central biomarker in invasive breast cancer, and the HER2 status has both important prognostic implications, and is predictive for the patient’s response to HER2-targeted treatment. According to the guidelines of the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP), the HER2 status must be determined by genetic and/or protein expression analysis of breast tissue sections using immunohistochemistry (IHC) and/or in situ hybridization (ISH), respectively.
The widely accepted ASCO/CAP recommendation for manual grading of breast cancer tissue sections stained by HER2 ISH is based on quantification of the HER2 gene amplification. Typically, the amplification is determined as the ratio between the number of HER2 gene probe signals and the number of centromer 17 probe signals within a selected tumor region. The ratio is divided into three intervals below 1.8, from 1.8 to 2.2, and above 2.2, corresponding to negative, equivocal, and positive for HER2 amplification, respectively.
The present protocol is based on the Visiopharm HER2 SISH algorithm, which by automated image analysis determines the HER2 amplification in brightfield digital images of breast cancer tissue sections stained by the INFORM™ HER2 Dual ISH assay from Ventana/Roche. This assay includes the HER2 Silver ISH (SISH) probe resulting in discrete or clustered small black signals, and the centromer 17 Fast Red ISH probe resulting in discrete red signals. The overall ratio of black to red signals constitutes the HER2 gene amplification. The amplification must be determined within regions of invasive tumor only, and as for the manual scoring method, the HER2 SISH algorithm therefore requires outlining of a relevant tumor region before the automated determination of signal numbers and amplification ratio.