context: Targeted therapy, also called biologic therapy, uses the body's immune system or hormonal system to fight breast cancer cells. That does less harm to healthy cells, so the side effects aren't usually as bad as from better-known treatments like chemotherapy. One type of targeted therapy uses antibodies to kill cancer cells or block them from growing. Antibodies are a part of the immune system made by special white blood cells. They can be made in a lab and given as medicine. Another type of this therapy uses drugs made of small molecules that block signals the cancer cells need to grow. The type of targeted therapy your doctor might recommend depends on the type of breast cancer you have. A gene called HER2 makes too many copies of itself in about 20% of people with breast cancer. If you have that faulty version of the gene, your disease is called " HER2-positive." Trastuzumab ( Herceptin) is the standard treatment for this type of breast cancer. It's one example of a lab-made antibody. Experts think it stops cancer cells from growing in three ways: It sticks to certain areas on cancer cells, stopping them from growing. It signals the body's immune system to attack cancer cells. It can help chemotherapy work better for you. Trastuzumab treats this type of breast cancer either alone or alone with chemotherapy drugs. Doctors commonly use it with drugs known as taxanes: docetaxel ( Docefrez, Taxotere) and paclitaxel ( Abraxane, Onxol). Pertuzumab ( Perjeta) is another antibody that treats HER2-positive breast cancer. Doctors use it along with docetaxel and trastuzumab. Pertuzumab may be harmful to a fetus, so women who are pregnant shouldn't take it. Another medication, ado-trastuzumab emtansine ( Kadcyla), combines the antibody in trastuzumab with a chemotherapy drug. Doctors give it to people with HER2-positive, advanced breast cancer who were already treated with trastuzumab. One possible drawback of antibody treatment is that you generally need to get it as a shot. Lapatinib ( Tykerb) is an example of a small-molecule drug that you can take in a pill. Together with chemotherapy, it treats some advanced cases of HER2-positive breast cancer. Doctors often use it when other cancer medications haven't worked for someone. If you don't have the faulty version of the HER2 gene that makes too many copies of itself, your disease is " HER2-negative." You'll need different treatments. If you've gone through menopause and have already tried certain treatments, your doctor might prescribe everolimus ( Afinitor) with exemestane ( Aromasin). Everolimus is for certain advanced cancers. Some postmenopausal women with certain types of advanced breast cancer may get a prescription for palbociclib ( Ibrance) or ribociclib ( Kisqali) along with hormone therapy. These drugs are used with an aromatase inhibitor such as anastrazole, exemastane, orletrozole ( Femara). Researchers are studying more ways to fight breast cancer. Angiogenesis inhibitors. These antibodies prevent the growth of new blood vessels, cutting off the supply of oxygen and nutrients to cancer cells. To date, the only such drug used for breast cancer, bevacizumab, lost its FDA approval because the risks outweighed its benefits and it didn't improve how long people with breast cancer lived. Signal transduction inhibitors. These antibodies block signals inside the cancer cell that help the cells divide, stopping the cancer from growing. These differ from one medicine to another. They can include: Allergic reactions Trouble breathing Swelling Nausea Rashes Diarrhea Fever Chills Dizziness Weakness Tell your doctor about any side effects you have. She may be able to ease them. Call your nurse or doctor if you have: A temperature over 100.4 F. If you have any fever and chills, tell your doctor immediately. If you can't reach your doctor, go to the emergency room. New mouth sores or patches, a swollen tongue, or bleeding gums A dry, burning, scratchy, or "swollen" throat A cough that is new or persistent Feeling the need to pee more often, stronger urges than usual, a burning feeling while peeing, or blood in your urine Heartburn, nausea, vomiting, constipation, or diarrhea that lasts longer than 2 or 3 days Blood in your stools Shortness of breath Swelling in feet or ankles Severe tiredness or fatigue