Endocrine Therapies for Breast Cancer: A Guide for Patients

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Endocrine therapies for breast cancer are often used as part of a comprehensive treatment plan for breast cancer, in addition to chemotherapy, surgery, and radiation therapy. These therapies are used to target the estrogen receptor-positive type of breast cancer, and this type of breast cancer accounts for approximately 65 percent of all cases. Taking a combination approach to treat breast cancer has made a large impact on improving survival rates. The Susan G. Komen Foundation states that the average five-year survival rate for breast cancer is higher than 95 percent, when diagnosed and treated early.

Blocking Estrogen

These therapies have a primary goal and that is to limit the ability of estrogen to reach the tumor cells that require estrogen for growth or to block estrogen production. The most invasive, though simplest, method of this therapy is to perform an oophorectomy, removing the ovaries surgically. When the ovaries are gone, little estrogen will be produced resulting in less estrogen for the tumor. This means that those with estrogen receptor-positive cancer, will experience better survival rates, whether it has spread to other areas of the body or is confined to the breast tissue. Women who wish to still have children may not find this the most desirable approach, however.

Drug Therapies

There are two types of drugs used as endocrine therapies for breast cancer. The choice endocrine therapy for women that are premenopausal are selective estrogen receptor modulators, a type of drug administered orally. These drugs work by blocking estrogen in the breast tissue. However, in other areas of the body, these drugs may produce effects similar to menopausal transition, such as sleeplessness, excessive sweating, hot flashes, and vaginal dryness.

Even in relatively advanced cases, these drugs can decrease tumor growth. These drugs may be prescribed as a preventative measure, even before cancer begins, in patients with a family history of breast cancer and in those who are high risk. These drugs have a high success rate. Studies have shown that in estrogen receptor-positive cancer, tumor growth reduction was seen in about 60 percent of women.

In addition to their powerful anti-cancer benefit, these drugs, such as tamoxifen, have also been shown to prevent or slow osteoporosis.

No drug is without risks. This type of drug may increase a patient’s risk of uterine cancer, venous blood clots in the legs, heart attack and stroke. Some women experience flares that consist of increased pain and tumor size increase in tumors near the surface of the skin.

Aromatase inhibitors work by blocking the body’s ways of producing estrogen with the aromatase enzyme. This type of drug is now a first-line therapy for postmenopausal women with metastatic estrogen-receptor positive breast cancer. They are also first-line adjuvant therapy for women beyond menopause with estrogen-receptor positive breast cancer that is considered “curable”. They are said to be more effective than selective estrogen receptor modulators.

This type of drug is also said to not increase the risk for cardiovascular problems or uterine cancer, but they do not protect against osteoporosis. In premenopausal women, this type of drug may cause painful, large cystic growths on the ovaries, therefore, they are not prescribed alone. When taking this type of drug, better survival rates are recorded for those with metastatic breast cancer.


National Cancer Institute. (2010). Adjuvant and Neoadjuvant Therapy for Breast Cancer. Retrieved on December 16, 2010 from the National Cancer Institute: https://www.cancer.gov/cancertopics/factsheet/Therapy/adjuvant-breast

Susan G. Komen. (2010). Updated Guidelines Address Hormonal Therapy for Breast Cancer. Retrieved on December 16, 2010 from Susan G. Komen: https://ww5.komen.org/KomenNewsArticle.aspx?id=6442452278