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The Abbott Molecular PathVysion HER2 (ERBB2) DNA Probe Kit is an FDA-approved kit used for evaluation of HER2 (ERBB2) gene amplification in breast cancer. The HER2 (ERBB2) oncogene is a member of the epidermal growth factor receptor family and has been found to be altered in approximately 20% of breast cancers. The PathVysion HER2 (ERBB2) DNA Probe Kit is a dual color probe kit that contains one probe (SpectrumOrange) specific for the HER2 (ERBB2) gene, and a second probe (SpectrumGreen) specific for chromosome 17. The underlying alteration is an amplification of the gene, resulting in more than the usual 2 copies of HER2 (ERBB2) (one on each copy of chromosome 17) typically present in normal breast epithelium and the majority of breast cancers without HER2 (ERBB2) alterations. Gene amplification is defined as a ratio of HER2 (ERBB2) to chromosome 17 signals of >2.2. Amplification of the HER2 (ERBB2) gene is almost always associated with overexpression of the HER2 (ERBB2) protein, as assessed by immunohistochemistry (IHC).
PhenoPath Laboratories has accumulated HER2 (ERBB2) protein IHC and FISH data in over 4,000 breast cancer patients over the past several years. These studies demonstrate the positive predictive value of a 3+ IHC study for HER2 (ERBB2) amplification by FISH is 94%, and the negative predictive value for a negative IHC study (i.e., a score of 0 or 1+) for non-amplification by FISH is 96%. A disproportionate fraction of the cases with discordant IHC and FISH results are cases of aneuploid tumors showing excess copies of chromosome 17, which may lead to overexpression of the protein, but without concomitant gene amplification (as the number of copies of the HER2 (ERBB2) gene might not be more than two-fold that of chromosome 17). We recommend the use of IHC as an initial screen for HER2 (ERBB2) status, with FISH studies performed on cases that show 2+ levels of immunostaining: i.e., cases indicated as showing an "indeterminate" HER2 (ERBB2) status by IHC.
HER2 (ERBB2) overexpression/gene amplification is an independent prognostic marker of adverse clinical outcome in breast cancer, and can predict response to doxorubicin (Adriamycin)-based adjuvant chemotherapy, as well as resistance to tamoxifen, even in the setting of ER/PR expression. Furthermore, HER2 (ERBB2) status also predicts response to immunotherapy with a "humanized" monoclonal antibody, trastuzumab (Herceptin) directed at the HER2 (ERBB2) protein.
Probe type: Dual color enumeration
CPT Code(s): 88374 (reference only; CPTs may vary)
Turnaround Time: Within 3-4 business days of receipt
Schedule: Monday - Friday
• Formalin-fixed, paraffin-embedded tissue block or cell block - OR -
• Minimum of 5 unstained slide cut at 4µm for each test requested
HER2 IHC slide (if no HER2 IHC slide is available, PhenoPath will perform and bill for the IHC, as needed, to interpret the HER2 FISH)