Tamoxifen is an antagonist of the estrogen receptor in breast tissue via its active metabolite, 4-hydroxytamoxifen. In other tissues such as the endometrium, it behaves as an agonist, and thus may be characterized as a mixed agonist/antagonist. Tamoxifen is the usual endocrine (anti-estrogen) therapy for hormone receptor-positive breast cancer in pre-menopausal women, and is also a standard in post-menopausal women although aromatase inhibitors are also frequently used in that setting.
Mechanism of action:
Tamoxifen is the most commonly used hormone therapy for the treatment of breast cancer.
Many women have breast cancer that tests positive for estrogen receptors (ER+). This means that estrogen promotes the growth of the breast cancer cells. Tamoxifen blocks the effects of estrogen on these cells. It is often called an “anti-estrogen.”
Tamoxifen slows or stops the growth of cancer cells that are already present in the body. It helps keep the original breast cancer from coming back and helps prevent new cancer in the opposite breast. It also reduces the risk of breast cancer in women who have a high risk for this disease.
Tamoxifen is used to prevent and treat breast cancers that test positive for estrogen receptors (ER+). It blocks the effects that the hormone estrogen has on cancer cells and lowers the chance that breast cancer will grow.
Has been used for decades to treat patients with advanced breast cancer.Is used after surgery or radiation therapy for early-stage breast cancer.Is used to prevent breast cancer in women who are high-risk for ER+ breast cancer.Can be used by women of all ages, both before and after menopause.Is being studied for the treatment of other types of cancer.
The most common side effects caused by tamoxifen are hot flashes; vaginal dryness, discharge, or irritation; and reduced interest in sex. These side effects are not usually serious, but they can be bothersome.
Other side effects are rare but are more dangerous. These include:
Overgrowth of the lining of the uterus (endometrial hyperplasia) and cancer of the lining of the uterus (endometrial cancer).An increased risk of blood clots in the legs (deep vein thrombosis) and the lungs (pulmonary embolism). Changes in the blood’s ability to clot have been reported in patients receiving tamoxifen.A small increased chance of stroke.Ovarian cysts.An increased risk of cataract formation and the need for surgery for cataracts.
Store at room temperature. Protect from heat, light and moisture. Keep away from reach of children.