Important Information for Your Healthcare Provider
You should talk with your healthcare provider prior to taking this medication if you have:
- Heart rhythm problems, including a condition known as QT prolongation or long QT syndrome
- Been told you have an electrolyte imbalance, such as low blood potassium (hypokalemia) or magnesium (hypomagnesemia)
- Congestive heart failure
- Unexplained vaginal bleeding
- A history of a blood clot or stroke
- Had endometrial hyperplasia (unusual growth and thickening of the lining of the uterus)
- Cancer that has spread to your bone
- Liver disease, such as hepatitis, cirrhosis, or liver failure
- Low white blood cells or platelets
- Any allergies, including to foods, dyes, or preservatives.
Also, let your healthcare provider know if you are:
Make sure to tell your healthcare provider about all other medications you are taking, including prescription and nonprescription medicines, vitamins, and herbal supplements.
As mentioned, toremifene belongs to a group of medications called selective estrogen receptor modulators. SERMs work by binding to estrogen receptors in the body.
Estrogen receptors are slightly different in various areas of the body, and the effects of SERMs can therefore vary by body tissue. In some body tissues, SERMs bind to estrogen receptors and have estrogenic effects (they act like estrogen). In other body tissues, SERMs bind to estrogen receptors and have anti-estrogenic effects (they block the effects of estrogen).
Many breast cancers
are estrogen sensitive, which means the tumor grows in response to estrogen. Breast cancer tumors that are sensitive to estrogen are known as estrogen receptor-positive tumors (or sometimes hormone receptor-positive tumors). They have estrogen receptors on their surface. When estrogen fits into these receptors, the tumor grows.
Toremifene works to treat breast cancer because it has anti-estrogenic effects on breast tissue. When the drug binds to the estrogen receptors on estrogen receptor-positive tumors, it prevents estrogen from also binding. As a result, estrogen cannot make the tumor grow and cancer progression is slowed down.