What is Hormone Therapy?
Chemotherapy uses cytotoxic drugs to kill cancer cells. By contrast, hormone therapy uses medications that prevent cancer cells from growing by changing normal body processes.
Hormones are natural chemicals produced by the body to regulate various processes such as blood sugar metabolism, bone growth, or milk production in the breasts. Hormones include such substances as adrenaline, insulin, and estrogen.
Certain types of breast cancers can grow only when there is a supply of the female hormone estrogen or progesterone. By treating the patient with chemicals that block the action of estrogen or progesterone, it is possible to slow down, or even stop, the growth of these cancer cells.
Do not confuse hormone therapy for treatment of breast cancer, with hormone replacement therapy, or HRT, for management of hot flashes and other symptoms during menopause. Different drugs, different goals.
How Does Hormone Therapy Work?
Those cancers that need estrogen or progesterone to grow, are made of cells equipped with hormone receptor sites scattered over their surface. These cancers are called estrogen or progesterone receptor positive, or ER- or PR-positive. Estrogen or progesterone molecules fit into the receptor sites like keys into locks, and stimulate the cells to divide. This makes the tumor grow faster.
Different hormone therapies work in one of several ways: by blocking the receptor sites, by eliminating receptor sites entirely, or by decreasing hormone production.
Blocking receptor sites: Tamoxifen and toremifene (Fareston)
These drugs, taken as daily pills, work by temporarily clogging the estrogen receptors site on the surface of the cancer cells, preventing estrogen molecules from binding to the cell. Think of it as the wrong key in a door lock: it fits, but won’t turn, and keeps out the right key. The result: the cells are not stimulated, and the tumor stops growing.
In women whose cancers are ER- or PR-positive, treatment with tamoxifen for five years reduces breast cancer recurrence by half. Tamoxifen has also been shown to be effective in reducing the development of breast cancer in those women who are at high risk for the disease.
Eliminating hormone receptor sites: Fulvestrant (Faslodex)
Faslodex works by eliminating the hormone receptors on the surface of the cells, making the cells insensitive to the growth-enhancing effect of hormones. Faslodex is given by injection, once a month.
Decreasing estrogen production: Aromatase inhibitors
Aromatase is a natural enzyme that helps produce small but significant amounts of estrogen in postmenopausal women. Inhibiting this enzyme can be an effective way of preventing the body from producing hormones in the first place.
Whether alone or in combination with tamoxifen, aromatase inhibitors have been shown to reduce the risk of breast cancer recurrence better than tamoxifen alone.
Decreasing estrogen production: Ovarian ablation
Premenopausal women, whose ovaries are a major source of estrogen and progesterone, have more limited choices of hormone therapy. By eliminating the ovaries surgically (by a procedure called oophorectomy) or chemically the women effectively become postmenopausal, and can take advantage of a wider variety of hormone treatment options.
Side Effects of Hormone Therapy
The side effects of hormone therapy vary with the type of therapy used. In general, hormone therapy has far fewer, and less severe, side effects than chemotherapy. Because hormone therapy blocks estrogen, it may cause the same symptoms as going through menopause, including hot flashes, changes in menstrual periods and vaginal dryness.
Hormone therapy may affect the rate of loss of calcium from bones, which may lead to osteoporosis. Ask your physician if you need a test called bone densitometry to determine whether your bones are in danger of becoming too brittle.
While you are on hormone therapy, you may still get pregnant, even if your periods have stopped as a result of the treatment. Since hormone therapy may be harmful to the fetus, it’s important to use birth control if you are sexually active. Do not use an oral contraceptive, or an injection or implant that contains hormones, since they may interfere with your hormone therapy. Instead, use a barrier method, such as a condom or a diaphragm.
Feel free to discuss with your doctor or nurse any sexual difficulties that you may be experiencing due to hormone therapy. Remember, there are many ways of helping you maintain your sexual activity even while you are being treated.
Even though you are being treated for cancer, your weight may increase, rather than decrease, sometimes by as much as 10-20 lbs. Many women find this side-effect distressing.
Who Should be Treated With Hormone Therapy?
Not all types of breast cancer can be treated with hormone therapy. To determine if hormone therapy is right for you, a sample of your tumor will be tested. If your tumor is estrogen receptor positive (ER+) or progesterone receptor positive (PR+), it means that the tumor can be stimulated by these hormones. In this case, your medical oncologist may recommend hormone therapy. If the tests are negative, hormone therapy will have no effect on the growth of your cancer.