Treatents can be classified into broad groups, based on how they work and when they are used.
Local therapy is intended to treat a tumor at the site without affecting the rest of the body. Surgery and radiation therapy are examples of local therapies.
Systemic therapy refers to drugs which can be given by mouth or directly into the bloodstream to reach cancer cells anywhere in the body. Chemotherapy, hormone therapy, and targeted therapy are systemic therapies.
Patients who have no detectable cancer after surgery are often given adjuvant (additional) systemic therapy. Doctors believe that in some cases cancer cells may break away from the primary breast tumor and begin to spread through the body by way of the bloodstream even in the early stages of the disease. These cells can't be felt on a physical exam or seen on x-rays or other imaging tests, and they cause no symptoms. But they can go on to become new tumors in other organs or in bones. The goal of adjuvant therapy is to kill these hidden cells.
Not every patient needs adjuvant therapy. Generally speaking, if the tumor is larger or the cancer has spread to lymph nodes, it is more likely to have spread through the bloodstream. But there are other features, some of which have been previously discussed, that may determine if a patient should get adjuvant therapy. Recommendations about adjuvant therapy are discussed in the sections on these treatments and in the section on treatment by stage.
Some patients are given systemic therapy, usually chemotherapy, before surgery to shrink a tumor in the hope it will allow a less extensive operation to be done. This is called neoadjuvant therapy.