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What is Fareston® ? (toremifene)

Fareston is a type of hormone therapy characterized as a SERM, a Selective Estrogen-Receptor Modulator. Toremifene is approved to treat metastatic breast cancer in women who are postmenopausal and whose tumors are estrogen-receptor positive. It may also be used for metastatic breast cancer in which the hormone receptor status of the breast cancer is unknown.1,2

Toremifene is manufactured by Kyowa Kirin.

What is the ingredient in Fareston?

The active ingredient in Fareston is toremifene, an estrogen agonist/antagonist.1

How does toremifene work?

Many breast cancers are hormone receptor positive (HR+). HR+ tumors have receptors for hormones, like the hormone estrogen, on the surface of their cells. When estrogen binds to these receptors, it can fuel the growth of the cancer cell.

Toremifene is sometimes referred to as an anti-estrogen. It binds to the estrogen receptors on breast cancer cells and blocks the estrogen in the body from getting into the cancer cells. By blocking the estrogen, toremifene can stop the growth of the cancer cells, which can lead to the cancer cells’ death.1,3

What are some of the possible side effects of toremifene?

Toremifene may cause serious side effects, such as a heart condition called QT interval prolongation, which can potentially lead to ventricular tachycardia (an abnormally fast heart rhythm) and may lead to seizure and/or death.1,2

Toremifene may also raise the levels of calcium in the blood (hypercalcemia) and cause a tumor flare in breast cancer patients where cancer has spread to the bones, especially within the first weeks after treatment is started. If hypercalcemia is severe, treatment with toremifene may potentially be discontinued by the patient’s doctor.1,2

The most common side effects experienced by patients taking toremifene in clinical trials include1:

Things to know about toremifene

Toremifene should not be used in women who have QT interval prolongation, uncorrected hypokalemia (low levels of potassium in the blood) or uncorrected hypomagnesemia (low levels of magnesium in the blood).1,2

Toremifene should not be used by anyone who has a known hypersensitivity (severe allergic reaction) to the drug.1,2

Before starting treatment with toremifene, patients should talk to their doctor about all their health conditions, especially if they have1,2:

  • Congestive heart failure
  • Liver disease or impairment
  • Abnormalities in electrolytes (like magnesium and potassium)
  • Endometrial hyperplasia
  • History of blood clots
  • If patients are pregnant, or planning to become pregnant

Before treatment with toremifene begins, patients should talk to their doctor about all medications (prescription and over-the-counter), vitamins, and herbal supplements they are taking. Some medications or supplements may interfere with each other and may cause side effects.1

Before beginning treatment with toremifene, patients may receive an electrocardiogram (ECG) to evaluate their heart function. Some patients may receive follow-up ECGs during treatment with toremifene.1,2

White blood cell counts and platelet counts should be monitored during treatment with toremifene in patients who have lowered blood cell counts.1,2

Toremifene is only approved for use in postmenopausal women and should not be used in women who are pregnant or planning to become pregnant. If premenopausal women who can become pregnant are prescribed toremifene, effective contraception should be used during treatment. Toremifene may cause harm to an unborn fetus. Patients should discuss effective contraception methods with their doctor.1,2

Dosing information

Toremifene comes in a 60 mg tablet to be taken once daily by mouth. It may be taken with or without food.1,2

For more information, read the full prescribing information for toremifene.

Patients should take their medication as prescribed by their doctor. Patients should talk to their doctor if they have any questions, or if they have questions regarding their toremifene regimen.

Written by: Editorial Team | Last reviewed: October 2019.
  1. Fareston prescribing information. Kyowa Kirin. Available at http://fareston.com/uploads/documents/fareston-pi.pdf. Accessed 9/25/18.
  2. Fareston product website. Kyowa Kirin. Available at http://fareston.com/. Accessed 9/25/18.
  3. Fareston. Chemocare. Available at http://chemocare.com/chemotherapy/drug-info/fareston.aspx. Accessed 9/25/18.