Chemo Prevention of Breast Cancer (2001)

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  • Women at low or normal risk of breast cancer (Gail risk assessment index <1.66% at 5 years): There is fair evidence to recommend against the use of tamoxifen to reduce the risk of breast cancer in women at low or normal risk of the disease. (grade D recommendation)
  • Women at higher risk of breast cancer (Gail index 1.66% at 5 years): Evidence supports counselling women at high risk on the potential benefits and harms of breast cancer prevention with tamoxifen. The cutoff for defining high risk is arbitrary, but the National Surgical Adjuvant Breast and Bowel Project P-1 Study included women with a 5-year projected risk of at least 1.66% according to the Gail index, and the average risk of patients entered in the trial was 3.2%. (grade B recommendation)



Examples of high-risk clinical situations are 2 first-degree relatives with breast cancer, a history of lobular carcinoma in situ or a history of atypical hyperplasia. As the risk of breast cancer increases above 5% and the benefits outweigh the harms, a woman may choose to take tamoxifen. The duration of tamoxifen use in such situations is 5 years based on the results from trials of tamoxifen involving women with early breast cancer.

If a woman raises concerns or has already been evaluated and is calculated to be at high risk, then individuals experienced and skilled in counselling may discuss the potential benefits and harms of tamoxifen use.