Herceptin is a liquid to be injected into a vein by a doctor or nurse in a hospital or medical facility. It must be given slowly, so the IV tube must remain in place for at least 90 minutes. Herceptin is usually given once a week when used to treat breast cancer that has spread to other areas of the body. When Herceptin is used to prevent the return of breast cancer, it is sometimes given once every 3 weeks and is sometimes given once a week along with other chemotherapy medications, and then once every 3 weeks after treatment with the other medications is completed. The length of your treatment depends on how well your body responds to the medication and the side effects that you experience. If you are using Herceptin to prevent the return of breast cancer, your treatment may last up to 52 weeks.