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Due to the availability of human epidermal growth factor receptor 2 (HER2)-directed therapies, testing for HER2 alterations, including overexpression, gene amplification or mutations is recommended in treatment guidelines for various tumor types, including breast cancer, gastric cancer, biliary tract cancer, cervical cancer, colorectal cancer, non-small cell lung cancer (NSCLC), and others.1-10
Human Epidermal Growth Factor Receptor 2 (HER2) aberrations, such as overexpression, HER2 gene amplification, and HER2 mutations, have been extensively researched and are associated with tumor proliferation in various solid tumor types including breast cancer, gastric cancer, gastroesophageal junction (GEJ) cancer, biliary tract cancer, colorectal cancer (CRC), non-small cell lung cancer (NSCLC), and bladder cancer.1 The presence of HER2 aberrations is linked to reduced survival, increased chance of brain metastasis, and treatment resistance.2
The 2018 guidelines from the American Society of Clinical Oncology (ASCO) and the College of American Pathology (CAP) classify human epidermal growth factor receptor-2 (HER2) status in breast cancer (BC) according to immunohistochemistry (IHC) staining results of biopsy specimens, ranging from IHC 0 to IHC 3+, plus in situ hybridization (ISH) test results.1
Human epidermal growth factor receptor-2 (HER2) is a member of the erythroblastic oncogene B (ERBB) family of transmembrane tyrosine kinase receptors that also includes epidermal growth factor receptor (EGFR, also known as HER1), and human epidermal growth factor receptors -3 and -4 (HER3, HER4).1,2 Despite being a receptor, HER2 has no known ligand, but its conformation is similar to the ligand-activated form of other ERBB family members, favoring heterodimerization with them.1,3