HER-2, a cellular receptor for epidermal growth factor, is a unique therapeutic target in breast cancer. In approximately 25% of cases, breast cancer cells over-express/amplify HER-2. Women with such over-expression tend to have more aggressive cancer. Recently, a humanised monoclonal antobody against HER-2 (trastuzumab/herceptin) has become available for therapy in clinical therapy of advanced breast cancer. In a recently reported trial involving 469 patients with metastatic breast cancer, 234 received standard chemotherapy and a further 235 received the same chemotherpy plus trastuzumab. The addition of trastuzumab to standard chemotherapy increased the objective response rate and response duration (New England J Medicine: 2001; 344: 783-92). An accompanying editorial (N Eng J Med 2001; 344: 841-2) considers this trial a landmark and it will have implications for future therapy.