HER2/Neu by FISH

Function

HER2 (Human Epidermal Growth Factor Receptor 2) is a protein that promotes the growth of cancer cells. Fluorescent In Situ Hybridization (FISH) is a molecular test used to see if the cancer cells have extra copies of the HER2 gene. More gene copies lead to more HER2 protein, making the cancer more aggressive.

Why it is Ordered

This test is standard of care for all newly diagnosed breast cancers and some gastric cancers. It is used to determine if a patient is a candidate for HER2-targeted therapies, such as Trastuzumab (Herceptin) or Pertuzumab (Perjeta). It is often performed after an IHC (Immunohistochemistry) test returns an 'equivocal' (2+) result.

Associated Conditions

• HER2-Positive Breast Cancer: A subtype of breast cancer that grows faster but responds well to targeted therapy.
• Gastric Adenocarcinoma: Some stomach cancers also overexpress HER2 and can be treated with targeted biologics.