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, see [1].
To determine the HER2/CEN-17 ratio, the total number of HER2 signals (Red) and the number of CEN-17 (Green) signals in the same 20 nuclei are identified. The total number of HER2 signals is then divided by the number of CEN-17 signals. Ratios above 2 are classified as amplified whereas ratios below 2 are classified un-amplified. Caution should be taken when intepreting on results near the cut-off (1.8 – 2.2). The operator only needs to define an overall region of interest.