Molecularly Targeted Therapies Researchers are constantly striving to find new ways to treat tumors. In recent years, scientists have been working on the development of new molecularly targeted therapies for various tumors, including breast, colorectal and lung cancers. The mechanism of action of targeted therapies is different from that of traditional chemotherapy in that it looks for specific markers on cancer cells or acts on specific aspects that affect cell growth. One type of targeted therapy is used specifically for progressive breast cancer, and it only inhibits breast cancer cells that produce too much HER2/neu protein. These cancer cells have a tendency to grow at an accelerated rate. This treatment works by binding to the HER2/neu protein (which is a receptor) on the tumor cells, stopping the HER2/neu protein from being active and the tumor cells from growing. It may be used in combination with chemotherapy. Certain side effects associated with targeted therapy include the following (but are not limited to), allergic reactions, heart-related illness, fever, diarrhea, infection, chills, frequent coughing, and headache. Talk to your doctor about what side effects you may experience and how to manage them accordingly. Always inform your doctor of side effects.