HER2 aberrations in cancer: Implications for therapy

Although anti-HER2 (human epidermal growth factor receptor 2) therapy is currently approved for breast, gastric, and gastroesophageal cancers overexpressing the HER2 protein or amplified for the HER2 gene, HER2 aberrations (gene amplification, gene mutations, and protein overexpression) are reported in other diverse malignancies. Indeed, about 1–37% of tumors of the following types harbor HER2 aberrations: bladder, cervix, colon, endometrium, germ cell, glioblastoma, head and neck, liver, lung, ovarian, pancreas, and salivary duct. Four HER2-targeted therapies have been approved for HER2-positive breast cancer: two antibodies (trastuzumab and pertuzumab), an antibody-drug conjugate (ado-trastuzumab emtansine), and a small molecule kinase inhibitor (lapatinib). In addition, afatinib, a small molecule kinase inhibitor that causes irreversible inhibition of EGFR (epidermal growth factor receptor) and HER2, was recently approved for EGFR-mutated non-small cell lung cancer. A large number of novel HER2-targeted agents are also in clinical trials. Herein we discuss the state of the art in understanding and targeting HER2 across anatomic tumor types.