What is the role of tamoxifen and raloxifene for the reduction of breast cancer risk?

Updated: Feb 04, 2021
  • Author: Pavani Chalasani, MD, MPH; Chief Editor: John V Kiluk, MD, FACS  more...
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wo selective estrogen receptor modulators (SERMs), tamoxifen and raloxifene, are approved for reduction of breast cancer risk in high-risk women. Two NSABP trials (P1 and P2) showed that tamoxifen reduced the risk of DCIS and invasive breast cancer by 30-50%. In the NSABP P2 prevention trial, raloxifene was as effective as tamoxifen in reducing the risk of invasive breast cancer but was 30% less effective than tamoxifen in reducing the risk of DCIS.

Tamoxifen use for 5 years reduces risk of breast cancer for at least 10 years in premenopausal women, particularly ER-positive invasive tumors. Women 50 years or younger have few adverse effects with tamoxifen, and vascular/vasomotor adverse effects do not persist after treatment.

As noted earlier, in an analysis that used pooled observational cohort data from 3 studies and included 1583 BRCA1 and 881 BRCA2 mutation carriers, adjuvant tamoxifen reduced the risk for contralateral breast cancer recurrences in women who carry these mutations. [127]

Tamoxifen and raloxifene are equally effective in reducing the risk of ER-positive breast cancer in postmenopausal women. Raloxifene is associated with lower rates of thromboembolic disease, benign uterine conditions, and cataracts than tamoxifen is. The evidence does not allow determination of whether either agent decreases mortality from breast cancer.

The aromatase inhibitors exemestane and anastrozole are used off label for breast cancer risk reduction in postmenopausal women. In the Mammary Prevention.3 (MAP.3) trial, conducted in 4560 postmenopausal women with moderately increased breast cancer risk, exemestane decreased the incidence of invasive breast cancer by 65% and that of invasive plus in situ breast cancer by 53%, compared with placebo. [161] In the International Breast Cancer Intervention Study II (IBIS-II), conducted in 3864 postmenopausal women at increased risk of developing breast cancer, after a median follow-up of 131 months, anastrozole was associated with a 54% decrease in ER-positive invasive breast cancer, and a 59% decrease in DCIS. [162]

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