What is adjuvant therapy for breast cancer?

Adjuvant therapy for breast cancer is any treatment given after primary therapy to increase the chance of long-term disease-free survival. Primary therapy is the main treatment used to reduce or eliminate the cancer. Primary therapy for breast cancer usually includes surgery—a mastectomy (removal of the breast) or a lumpectomy (surgery to remove the tumor and a small amount of normal tissue around it; a type of breast-conserving surgery). During either type of surgery, one or more nearby lymph nodes are also removed to see if cancer cells have spread to the lymphatic system. When a woman has breast-conserving surgery, primary therapy almost always includes radiation therapy.

Even in early-stage breast cancer, cells may break away from the primary tumor and spread to other parts of the body (metastasize). Therefore, doctors give adjuvant therapy to kill any cancer cells that may have spread, even if they cannot be detected by imaging or laboratory tests. Studies have shown that adjuvant therapy for breast cancer may increase the chance of long-term survival by preventing a recurrence (1).

What types of adjuvant therapies are used for breast cancer?

Most adjuvant therapies are systemic: they use substances that travel through the bloodstream, reaching and affecting cancer cells all over the body. Adjuvant therapy for breast cancer can include chemotherapy, hormonal therapy, the targeted drug trastuzumab (Herceptin), radiation therapy, or a combination of treatments.

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Adjuvant chemotherapy uses drugs to kill cancer cells. Research has shown that adjuvant chemotherapy for early-stage breast cancer helps to prevent the cancer from returning (1). Usually, more than one drug is given during adjuvant chemotherapy (called combination chemotherapy).

Hormonal therapy deprives breast cancer cells of the hormone estrogen, which many breast tumors need to grow. A commonly used hormonal treatment is the drug tamoxifen, which blocks estrogen’s activity in the body. Studies have shown that tamoxifen helps prevent the original cancer from returning and also helps to prevent the development of new cancers in the other breast; however, many women develop resistance to the drug over time (1, 2). Tamoxifen can be given to both premenopausal and postmenopausal women.

Postmenopausal women may also receive hormonal therapy with a newer type of drug called an aromatase inhibitor (AI), either after tamoxifen therapy or instead of tamoxifen therapy. Rather than blocking estrogen’s activity, as tamoxifen does, AIs prevent the body from making estrogen. Clinical trials suggest that AIs may be more effective than tamoxifen in preventing breast cancer recurrence in some women (3–6). Using AIs to block estrogen production in premenopausal women is not very effective, in part because the ovary is stimulated to make more estrogen when blood levels of estrogen fall below normal. This does not occur in postmenopausal women, whose ovaries have stopped making estrogen.

Some premenopausal women may undergo ovarian ablation or suppression, which greatly reduces the amount of estrogen produced by the body, either permanently or temporarily. Premenopausal women who have BRCA1 or BRCA2 gene mutations are at very high risk of breast cancer recurrence as well as of ovarian cancer and may decide to have their ovaries surgically removed as part of adjuvant therapy. The surgical removal of the ovaries also decreases the risk of ovarian cancer. Other premenopausal women who have a lower risk of recurrence may be prescribed drugs that temporarily suppress the function of the ovaries, in addition to tamoxifen.

Trastuzumab is a monoclonal antibody that targets cancer cells that make too much of, or overexpress, a protein called HER2. When cancer cells overexpress HER2 protein, they are said to be HER2 positive. Approximately 20 percent of all breast cancers are HER2 positive. Clinical trials have shown that targeted therapy with trastuzumab in addition to chemotherapy decreases the risk of relapse for women with HER2-positive tumors (7–9).

Radiation therapy is usually given after breast-conserving surgery and may be given after a mastectomy. (When doctors give radiation therapy after breast-conserving surgery, it is usually considered part of primary therapy.) For women at high risk of recurrence, doctors may use radiation therapy after mastectomy to kill cancer cells that may be left in tissues next to the breast, such as the chest wall or nearby lymph nodes. Radiation therapy is a type of local therapy, not systemic therapy.

How is adjuvant therapy given, and for how long?

Adjuvant chemotherapy is given orally (by mouth) or by injection into a blood vessel. It is given in cycles, consisting of a treatment period followed by a recovery period. The number of cycles depends on the types of drugs used. Most patients do not have to stay in the hospital for chemotherapy—they can be treated as an outpatient or at the doctor’s office. Adjuvant chemotherapy usually does not last for much more than 6 months.

Hormonal therapy is usually given orally, as a pill.

  • Most women who undergo hormonal therapy take tamoxifen every day for 5 years.
  • Some women may take an aromatase inhibitor every day for 5 years instead of tamoxifen.
  • Some women may receive additional treatment with an aromatase inhibitor after 5 years of tamoxifen.
  • Finally, some women may switch to taking an aromatase inhibitor after 2 or 3 years of tamoxifen, for a total of 5 or more years of hormonal therapy.

Trastuzumab is given by infusion into a blood vessel every 1 to 3 weeks for a year.

Radiation therapy given after mastectomy is divided into small doses given once a day over the course of several weeks. Radiation therapy may not be given at the same time as some types of chemotherapy or hormonal therapy.