Oncology Encyclopedia:
Toremifene |
Key Terms: Adjuvant, Anticoagulant, Apoptosis, Granulosa cells, Oncogene, Ovarian follicle.
Definition
Toremifene, also known as Fareston, is a synthetic compound similar to estrogen. It mimics the action of estrogen on the bones and uterus, but blocks the effects of estrogen on breast tissue.
Purpose
Toremifene is used as adjuvant hormone therapy immediately after surgery in early stages of breast cancer and also to treat advanced metastatic breast cancer (stages III and above) in postmenopausal women. Postmenopausal women at high risk of developing breast cancer may take toremifene to reduce risk.
Description
Toremifene is similar to tamoxifen in structure and action. Toremifene can be given as sole treatment, but it is often given in combination with other chemotherapeutic drugs.
Toremifene belongs to a family of compounds called antiestrogens. Antiestrogens are used in cancer therapy by inhibiting the effects of estrogen on target tissues. Estrogen is a steroid hormone secreted by granulosa cells of a maturing follicle within the female ovary. Depending on the target tissue, estrogen can stimulate the growth of female reproductive organs and breast tissue, play a role in the female menstrual cycle, and protect against bone loss by binding to estrogen receptors on the outside of cells within the target tissue. Antiestrogens act selectively against the effects of estrogen on target cells in a variety of ways, thus they are called selective estrogen receptor modulators (SERMs).
Toremifene selectively inhibits the effects of estrogen on breast tissue, while mimicking the effects of estrogen on bone (by increasing bone mineral density) and uterine tissues. The former makes toremifene an excellent therapeutic agent against breast cancer. Although researchers are unclear of the precise mechanism by which toremifene kills breast cancer cells, it is known to compete with estrogen by binding to estrogen receptors, therefore limiting the effects of estrogen on breast tissue. Toremifene also may be involved in other anti-tumor activities affecting oncogene expression, promotion of apoptosis and growth factor secretion.
In 2003, clinical trials were underway to test toremifene citrate for treating complications of certain therapies for prostate cancer patients. For example, androgen deprivation therapy results in increased bone fractures among prostate cancer patients. Researchers believe that toremifene citrate will help reduce these and other effects.
Recommended Dosage
Toremifene is taken orally, and the recommended dose is usually 40 to 60 milligrams once a day, although larger doses are sometimes prescribed. If a dose is missed, patients should not double the next dosage. Instead, they should return to their regular schedule and contact their doctor.
Precautions
Toremifene is not recommended for use in children. Women who are pregnant or nursing should not use this drug since it has several side effects that, although rare, can be severe. It is known to cause miscarriages and birth defects. Women are encouraged to use birth control while taking toremifene. However, oral contraceptives can negatively alter the effects of toremifene. Therefore, patients should explore other birth control options.
Great care should be exercised when toremifene is used with warfarin, an anticoagulant, because toremifene can amplify the effects of warfarin, prolonging bleeding times. The result could possibly be fatal. Patients who are predisposed to the formation of thromboembolisms should use toremifene with caution, because toremifene can increase the risk.
Side Effects
Although toremifene is usually well tolerated by patients, there are some side effects. One of the most serious side effects is development of uterine cancer. Less common effects include eye problems such as retinal lesions, macular edema and corneal changes (most resolve themselves after use is discontinued); neurological problems such as depression, dizziness, confusion, and fatigue; and genital problems such as vaginal bleeding, vaginal discharge, and endometriosis. Patients also may experience liver problems.
Interactions
Toremifene can interfere with the anticoagulant drug warfarin, resulting in severe consequences and death. If these two drugs are used together, patients will be monitored closely. Oral contraceptives and estrogen supplements can also interfere with the action of toremifene.
Resources
Periodicals
"GTx Starts Phase III Study With Prostate Cancer Drug." BIOWORLD Today 219 (November 11, 2003).
—Sally C. McFarlane-Parrott; Teresa G. Odle
