Breast cancer chemoprevention: Medicines that reduce breast cancer risk

Preventive medications (chemoprevention) reduce breast cancer risk in women at high risk of developing the disease. Find out how these medications work plus associated side effects and health risks.

By Mayo Clinic Staff

If you're at high risk of breast cancer, you may be able to improve your odds of staying cancer-free by taking certain medicines, an approach known as chemoprevention or preventive therapy.

Medications for breast cancer chemoprevention are the subject of much ongoing research.

Here's a look at what's known about each of these medications, including how they may work to prevent breast cancer and the possible side effects and health risks.

Tamoxifen

How it works

Tamoxifen blocks the effects of estrogen — a reproductive hormone that influences the growth and development of many breast tumors.

Tamoxifen belongs to a class of drugs known as selective estrogen receptor modulators (SERMs), and it reduces the effects of estrogen in most areas of the body, including the breast. In the uterus, tamoxifen acts like an estrogen and encourages the growth of the lining of the uterus.

Tamoxifen is prescribed as a pill you take once a day by mouth. For breast cancer risk reduction, tamoxifen is typically taken for a total of five years. The risk reduction benefit continues for 10 years after you stop taking tamoxifen.

Who it's for

Tamoxifen is used to reduce the risk of invasive breast cancer in high-risk women age 35 and older, whether or not they've gone through menopause.

Generally speaking, you and your doctor might consider whether chemoprevention with tamoxifen is right for you if:

  • Your Gail model risk score is greater than 1.66 percent. The Gail model is a tool doctors use to predict future risk of developing breast cancer, based on factors such as your age, reproductive history and family history.
  • You're at high risk of developing breast cancer — for instance, you've had a breast biopsy that found a precancerous condition such as lobular carcinoma in situ (LCIS), atypical ductal hyperplasia or atypical lobular hyperplasia.
  • You have a strong family history of breast cancer.
  • You don't have a history of blood clots.

Common side effects

Common side effects of tamoxifen include:

  • Hot flashes
  • Night sweats
  • Vaginal discharge
  • Vaginal dryness

Risks

Rarely, taking tamoxifen may cause:

  • Blood clots
  • Endometrial cancer or uterine cancer
  • Cataracts
  • Stroke

The risk of uterine cancer for premenopausal women taking tamoxifen is very low, compared with those who have undergone menopause. The benefits of tamoxifen outweigh the risks in premenopausal women who have an increased risk of breast cancer due to a strong family history of the disease or a personal history of precancerous breast changes.

In women who have undergone menopause, the benefits of tamoxifen may outweigh the risks in women who have an increased risk of breast cancer and have also had surgery to remove the uterus (hysterectomy).

Feb. 12, 2014 See more In-depth