Evidence Summary

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Tamoxifen and raloxifene each reduce invasive breast cancer; neither reduces mortality rates in the particular group

Nelson H, Smith B, Griffin J, et al. Use of medications to reduce risk for primary breast cancer: a systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2013.158:604-14.

Review question

What is the current evidence on medications to reduce the risk for primary breast cancer?


One U.S. health group has recommended medications to reduce the risk for primary breast cancer in women at an increased risk.

Studies show the effectiveness of several medications for breast cancer. Tamoxifen and raloxifene are the only approved medications for this purpose. And raloxifene is approved for post-menopausal women only. Their use is low.

It is not clear how to select patients for these medications. In addition to benefits, they may cause adverse health effects.

How the review was done

This summary is based on a systematic review of 7 randomized controlled trials (or RCTs) of the drugs tamoxifen or raloxifene in women who do not have breast cancer.

The studies compared tamoxifen with raloxifene, tamoxifen with placebo, and raloxifene with placebo.

The review looked at the effectiveness and the adverse effects. It also considered patient use of such medications and methods for identifying women at increased risk for breast cancer.

The U.S. Agency for Healthcare Research and Quality funded this research.

What the researchers found

Tamoxifen and raloxifene reduced the incidence of invasive breast cancer by 7 to 9 cases in 1,000 women over 5 years compared with placebo.

New results from the Study of Tamoxifen and Raloxifene showed that tamoxifen reduced breast cancer incidence more than raloxifene by 5 cases in 1,000.

Neither medication reduced significantly noninvasive cancer incidence or mortality rates.

Both tamoxifen and raloxifene reduced the incidence of fractures. Tamoxifen increased the incidence of cataracts more than raloxifene and placebo.


Tamoxifen and raloxifene reduce the incidence of invasive breast cancer and fractures.  They also increase the incidence of clot formation.

Results comparing tamoxifen and raloxifene


Tamoxifen and raloxifene

Invasive breast cancer

Both reduced incidence by 7 to 9 cases in 1,000 women over 5 years.

Relative effectiveness

Tamoxifen had greater effect on cancer incidence than raloxifene.


Neither reduced cancer-specific or all-cause mortality rates.


Both reduced incidence of fractures.

Clot formation

Tamoxifen increased incidence more than raloxifene by 4 cases in 1,000.

Uterus lining cancer

Tamoxifen increased incidence more than raloxifene and placebo (4 cases in 1,000).


Tamoxifen increased incidence more than raloxifene and placebo.



A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.

Related Web Resources

  • Breast cancer: Risks and benefits, age 50-69

    Canadian Task Force on Preventive Health Care
    Your risk of dying from breast cancer is slightly reduced if you have regular screening. However, regular screening increases your chance of a false positive result, a biopsy and having part or all of a breast removed unnecessarily.
  • Breast cancer: Patient algorithm

    Canadian Task Force on Preventive Health Care
    The Canadian Task Force on Preventive Health Care recommends women between 50 and 74 years old who are not at high risk get screened for breast cancer every 2 to 3 years. Talk to your doctor about screening options if you are at high risk or over 74 years old.
  • Breast cancer: Patient FAQ

    Canadian Task Force on Preventive Health Care
    This resource includes frequently asked questions about breast cancer, including: Who is considered high risk? What are the harms associated with mammography? and Why is routine screening NOT recommended for women 40-49 years?
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