The tyrosine kinase inhibitor imatinib mesylate (Gleevec®), for the treatment of Philadelphia chromosome-positive chronic myelogenous leukemia and KIT-positive gastrointestinal stromal tumors [63, 64], as well as the monoclonal antibody trastuzumab (Herceptin®) directed against HER2-positive breast cancer and gastroespohageal cancer [65], are two notable examples of targeted therapies with high activity in subsets of tumors. Here, ERBB2 is linked to breast carcinoma.