What Is Fareston® (toremifene)?

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Fareston® (toremifene) is a type of hormone therapy known as a selective estrogen-receptor modulator (SERM). It is used to treat metastatic breast cancer (cancer that has spread) in women who are past menopause and whose tumors are estrogen-receptor positive. It may also be used for metastatic breast cancer with unknown hormone receptor status.1,2

What are the ingredients in Fareston?

The active ingredient in Fareston is toremifene.1

How does toremifene work?

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

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

What are the possible side effects?

The most common side effects of toremifene include:1,2

Toremifene may also cause serious side effects, including:1,2

  • Increased risk of uterine cancer
  • Increased calcium levels in the blood (hypercalcemia)
  • Blood clots
  • Tumor flare
  • Liver problems

Toremifene has a boxed warning, the strictest warning from the U.S. Food and Drug Administration (FDA). This is because it may cause a heart condition called QT interval prolongation. This can lead to an abnormally fast heart rhythm (ventricular tachycardia) and may lead to seizure and/or death.1,2

These are not all the possible side effects of toremifene. Talk to your doctor about what to expect or if you experience any changes that concern you during treatment with toremifene.

Other things to know

Toremifene should not be used in people who have:1,2

  • QT interval prolongation
  • Low levels of potassium in the blood (hypokalemia)
  • Low levels of magnesium in the blood (hypomagnesemia)

Before and during treatment with toremifene, your doctor will monitor your:1,2

  • Blood counts
  • Calcium levels
  • Liver function
  • Heart function (in patients at risk of QT interval prolongation)

Before starting treatment with toremifene, tell your doctor if you have:1,2

  • Congestive heart failure
  • Liver problems
  • Abnormalities in electrolytes (like magnesium and potassium)
  • Endometrial hyperplasia
  • History of blood clots

Toremifene can harm an unborn baby. If you can become pregnant, you should use birth control during treatment with toremifene. You should also not breastfeed during treatment with toremifene. Talk to your doctor about your options for birth control and breastfeeding while taking toremifene.1,2

Before beginning treatment for breast cancer, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you are taking. This includes over-the-counter drugs.

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

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