Angiogenesis. The growth of new blood vessels from preexisting vasculature

Epidermal growth factor receptor (EGFR, also known as HER1). A tyrosine kinase that, when activated by binding of specific ligands, triggers intracellular signaling that ultimately leads to cell proliferation, invasion, and migration; it is a target of treatment (with the monoclonal antibodies cetuximab [Erbitux] and panitumumab [Vectibix], and the small molecule inhibitors erlotinib [Tarceva], gefitinib [Iressa], and lapatinib [Tykerb]) in multiple tumor types

Fragment antigen binding (Fab). The region of an antibody responsible for recognizing and binding to antigens

Fragment crystallizable (Fc). The region of an antibody responsible for interacting with immune system components such as natural killer cells and the complement cascade; in some instances, it may be conjugated to a lethal payload such as a radioisotope or toxin

HER2/neu. A tyrosine kinase related to epidermal growth factor receptor; it has a role in the pathogenesis of breast cancer and is a target of treatment (with the monoclonal antibody trastuzumab [Herceptin] and the small molecule inhibitor lapatinib [Tykerb]) in the 25 percent of persons with breast cancer in which HER2/neu is overexpressed. Overexpression of HER2/neu is associated with disease recurrence and worse prognosis. HER2 is named because it has similar structure to human epidermal growth factor receptor (HER1); neu is so named because it was derived from a neuroglioblastoma cell line

Ligand. A molecule that binds to a specific receptor

Monoclonal antibodies. Identical antibodies produced by a single type of immune cell; in targeted cancer therapy, they are directed against molecules unique to, overexpressed in, or mutated in cancer cells

Small molecule inhibitors. Drugs that interfere with the function of molecules involved in the development and progression of cancer; most commonly, they interfere with tyrosine kinases

Tyrosine kinase. Enzyme that transfers a phosphate group from adenosine triphosphate to a tyrosine amino acid residue in a protein, which may then trigger downstream molecular signaling

Vascular endothelial growth factor (VEGF). A signaling protein involved in angiogenesis; it binds to tyrosine kinases (VEGF receptors) to initiate and promote angiogenesis. It is a target of treatment with the monoclonal antibody bevacizumab (Avastin)