Q: Do the benefits of tamoxifen in treating breast cancer outweigh its risks?

A: The National Cancer Institute states: "The benefits of tamoxifen as a treatment for breast cancer are firmly established and far outweigh the potential risks. Patients who are concerned about the risks and benefits of tamoxifen or any other medications are encouraged to discuss these concerns with their doctor."

Cancer Types - About Tamoxifen

What is tamoxifen?

Tamoxifen (Nolvadex®) is a drug that reduces and/or stops the effects of estrogen (a female hormone) in the body. It was developed over 20 years ago and has been used to treat both advanced and early stage breast cancer. More recently, tamoxifen is being used as an adjuvant, or additional, therapy following primary treatment for early stage breast cancer.

Tamoxifen is taken by mouth in tablet form and is usually prescribed as a single daily dose.

How is tamoxifen used for breast cancer treatment?

As a breast cancer therapy, tamoxifen works against the effects of estrogen, which has been shown to promote the growth of breast cancer cells. It is often called an "anti-estrogen."

  • As a treatment for breast cancer, the drug slows or stops the growth of cancer cells that are already present in the body.
  • As adjuvant therapy, tamoxifen has been shown to help prevent the development and recurrence of breast cancer. Research has shown that when tamoxifen is used as adjuvant therapy for early stage breast cancer, it not only prevents the recurrence of the original cancer but also prevents the development of new cancers in the opposite breast, in many cases.
  • As a preventative therapy, tamoxifen has been shown to help prevent the development of breast cancer in high-risk women. The Study of Tamoxifen and Raloxifene (STAR) trial, which evaluated the use of tamoxifen and another drug, raloxifene, in preventing breast cancer, found that raloxifene decreased the risk of invasive breast cancer equally as well as tamoxifen, but it did not protect as well against non-invasive cancers, such as lobular carcinoma in situ (LCIS) or ductal carcinoma in situ (DCIS). Raloxifene did, however, have a lower risk of uterine cancer and blood clots in the legs or lungs, compared to tamoxifen.

Additional benefits of tamoxifen:

While tamoxifen acts against the effects of estrogen in breast tissue, it acts like estrogen in other body systems. According to the National Cancer Institute, women who take tamoxifen may share many of the beneficial effects of menopausal estrogen replacement therapy, such as a lowering of blood cholesterol and a slowing of bone loss (osteoporosis).

What are the possible side effects of tamoxifen?

Women considering taking tamoxifen should consult their physician. Different women experience side effects differently. Some of the more common side effects may include:

  • hot flashes and sweats
  • nausea and vomiting
  • loss of appetite
  • weight gain
  • vaginal discharge
  • irregular menstrual cycles
  • fatigue
  • headache
  • vaginal dryness
  • irritation of skin around the vagina

Less common side effects may include:

  • blood clots
  • depression
  • eye problems
  • uterine cancer
  • other cancers

Some physicians and researchers caution, however, that tamoxifen therapy may not be appropriate for all women who are at increased risk for breast cancer. Consult your physician for more information regarding your individual case.

Other related medications:

Medications recently approved by the US Food and Drug Administration (FDA), called aromatase inhibitors, are used to prevent the recurrence of breast cancer in postmenopausal women. These drugs, such as anastrozole (Arimidex®), letrozole (Femara®), and exemestane (Aromasin®), prevent estrogen production. Possible side effects of these drugs include osteoporosis or bone fractures.

Another new drug for recurrent breast cancer is fulvestrant (Faslodex®). Also approved by the FDA, this drug eliminates the estrogen receptor rather than blocking it, as is the case with tamoxifen, letrozole, or anastrozole. This drug is used following previous antiestrogen therapy. Side effects for fulvestrant include hot flashes, mild nausea, weight gain, and fatigue.

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