While there are many different types of drugs used to treat different types of cancer, the actual method of chemotherapy treatment falls into one of two classifications: adjuvant and neoadjuvant. The classification is determined by the order in which treatment is issued. Surgery is usually considered to be primary therapy. This includes mastectomies (total removal of the breast) or a lumpectomy (breast conserving surgery which only removes the cancerous tissue and the tissue immediately surrounding it). Both types of surgery can include removal of affected lymph nodes to determine if the cancer has spread to the lymphatic system.

In adjuvant therapy, the patient has surgery first to remove the tumor and affected tissue, followed by other treatments such as chemotherapy, targeted therapy (Herceptin/trastuzumab), hormonal therapies, radiation therapy, or a combination of these. Adjuvant therapy is used to treat any cancer cells that remain in the body after surgery, as surgery is usually unable to fully remove all the cancer cells in the body.  There is a tendency for radical cancer cells to exist in the body separate from the tumor itself without causing metastases. General chemotherapy is used to treat these cancer cells and prevent the cancer from returning. For breast cancer that is HER2+, Herceptin targeted therapy is used to treat the cancer and prevent recurrence. HER2+ cancer cells create too much HER2 protein. For breast cancer that is estrogen receptive, a drug called tamoxifen, which is an estrogen blocker, is used to prevent recurrence and stop new cancers from developing. It is possible for women to develop a resistance to the drug, as it is often given for a period of several years. Women who are postmenopausal instead of using tamoxifen, may receive aromatase inhibitors since the ovaries are no longer the source of estrogen. Premenopausal women may choose to go through a process called ovarian ablation, or suppression, to significantly reduce the amount of estrogen the ovaries produce. These results can be temporary or permanent depending on the person. Women who are premenopausal and are BRCA1 or BRCA2 positive, meaning they have a genetic mutation that predisposes them to cancer, may choose to have their ovaries removed to decrease their risk of developing subsequent ovarian cancer. Radiation, which is local therapy as opposed to systemic, may also be used  to kill cancer cells that remain at the surgery site. When given after surgery, radiation is considered to be of the primary therapy. Radiation may be used after both mastectomies and lumpectomies. Adjuvant chemotherapy usually does not last more than six months, Herceptin treatment usually last one to two years, hormonal therapy can last as long as five years, and radiation therapy is usually administered daily over the course of several weeks.

Adjuvant therapy is used for patients with significant risk of recurrence and is based on the cancer stage and size, grade, proliferative capacity (how fact the tumor grows), hormone receptor status, and HER2 status. Hormone receptor status and HER2 status are major factors in determining which medications will be used during treatment. Although determining the likelihood of recurrence is not an exact science, doctor’s use historical data to determine the best course of action, and include in their consideration the individual patient’s general health beyond the cancer, personal preferences for her treatment, and lifestyle factors.

Source: Cancer.gov