Types of Hormone Therapy for Breast Cancer
Written by : Dr.M.D.Mazumdar, MD
Hormone therapy for breast cancer is aimed at either reducing the level of estrogen in the body, or preventing the estrogen already produced from acting on the receptors in the breast cells.
(Click this link to know how hormone therapy works.)
The duration of treatment may vary from person to person and from drug to drug but the most common treatment duration is 5 years. If hormone therapy is prescribed for recurrence or due to metastatis of the cancer, it is continued for more than 5 years and as long as it takes to control the cancer.
Types of Hormone Therapy
There are three main groups of drugs used in hormone therapy:
- Aromatase Inhibitors (AI): These drugs are prescribed for women who develop breast cancer after the menopause or in whom the ovaries have been removed. Hormone-dependent breast cancer needs the hormone estrogen to grow. After the age of menopause, estrogen is mainly produced from androgens (male hormones) by an enzyme (called aromatase). Androgens are produced by the adrenal glands in both males and females. Aromatase inhibitors decreases the body's estrogen level by blocking aromatase from producing estrogen.
- Anastrozole (Arimidex)
- Exemestane (Aromasin)
- Letrozole (Femara)
Aromatase Inhibitors are commonly prescribed together with SERMs like Tamoxifen. After surgery, taking a AI and a Tamoxifen, either together, or one after the other, has shown to decrease the risks of recurrence of breast cancer.
AIs are given orally as pills in a single daily dose.
- Selective Estrogen Receptor Modulators (SERMs): Besides the breasts, estrogen receptors are present in other parts of the body like the bones and the uterus. But SERMs mainly block the effect of estrogen on the breast tissue .
While the SERMs used in different breast cancers act as anti-estrogen in breast cells, they act like an estrogen in other tissues, like the uterus and the bones. Hence the term "selective".
SERMS act on the receptors by sitting on their surface and preventing the estrogen from attaching to the cells. If estrogen isn't attached to a breast cell, the cell does not receive estrogens signals to grow and multiply.
SERM's are usually prescribed for women who are still menstruating and have not yet attained menopause and has not started showing any of the menopausal symptoms. They can be prescribed after surgery (adjuvant therapy) or before surgery (neoadjuvant therapy). The duration of treatment is usually five years. There are three SERMs commonly used:
- Tamoxifen (Nolvadex)
- Raloxifene (Evista)
- Toremifene (Fareston)
Of these three drugs, Tamoxifen is the most widely used. It can be used in both premenopausal as well as menopausal women. Toremifene (Fareston) is generally used in metastatic breast cancers. Both are prescribed daily in pill form.
- Estrogen Receptor Downregulators (ERDs): The action of ERDs are similar to SERMs - they block the estrogen receptors so that the estrogen cannot attach to the receptor. This prevents growth and multiplication of the cell. But they also work in two other ways - they can reduce the number of estrogen receptors and they can change the shape of breast cell estrogen receptors so that they don't work very well. Unlike a SERM, ERDs act like an anti-estrogen throughout the body.
It is commonly used in metastatic breast cancer when tamoxifen and/or other SERMs have stopped working.
ERDs are given in the injectible form. Initially, for the first month, the shots are given 2 weeks apart. After that, they are given once a month.
There is only one ERD available:
- Fulvestrant (Faslodex)
Drugs used for Treatment of Breast Cancer
Other Treatments to Decrease Estrogen Levels in the Body
In premenopausal women, the level of estrogen can be brought down by stopping the ovaries from producing estrogen or by removing the ovaries. This is called 'ovarian ablation'.
- Pituitary Downregulation The pituitary gland in the brain produces a hormone called FSH which stimulates the ovaries to produce estrogen. Certain drugs can act on the pituitary to prevent secretion of FSH. With less FSH in the blood, the ovaries are not sitmulated to produce estrogen. These drugs are also called LHRH analogues or 'luteinising hormone releasing hormone' analogues or GnRH agonists. The drugs commonly used are:
- Goserelin (Zoladex).
- Leuprolide (Lupron).
- Ovarian Ablation: In pre-menopausal women, decreasing the estrogen level by ovarian suppression (ablation) has shown good results in treatment of breast cancer as well as preventing recurrence. This can be done by:
- Surgical Removal of the ovaries
- Aiming radiation at the ovaries to ablate and destroy them. This is not commonly done nowadays.
- Surgical Removal of the ovaries
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