Chemotherapy is a treatment that slows or kills breast cancer cells. It often uses a combination of drugs to be more effective. These may be administered orally or intravenously, and treatment may last from several months up to a year. Chemo may be given after a mastectomy or lumpectomy in breast cancer, or it may be given as the main treatment if cancer has spread. Your doctor can perform certain tests to determine if treatment is working. Follow the links below to find WebMD's comprehensive coverage about how breast cancer chemotherapy is performed, what to expect, and much more.